GEOMATICS & VOCABULARY -...

Biuro Projektu al. Tysiąclecia Państwa Polskiego 7, 25-314 Kielce

tel. 41-34-24-209, e-mail: [email protected]

Projekt ,,Politechnika Świętokrzyska – uczelnia na miarę XXI w.’’ Program Operacyjny Kapitał Ludzki Priorytet IV Działanie 4.1, Poddziałanie 4.1.1

na podstawie umowy z Ministerstwem Nauki i Szkolnictwa Wyższego UDA – POKL.04.01.01-00-381/10-00

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MATERIAŁY DYDAKTYCZNE DO PRZEDMIOTU

GEOMATICS & VOCABULARY

Wykłady 15 h

Wydział Inżynierii Środowiska, Geomatyki i Energetyki

Opracował - Ryszard Florek Paszkowski





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CONTENTS

1. APPLICATION OF A FILM CAMERA TO HIGH VARIABILITY DEFLECTION

PHOTOGRAMMETRIC MEASUREMENTS OF LIGHTING METALLIC TOWERS. 3

1.1. Introduction. 3

1.2. The object of measurements 3

1.3. Photogrammetric method of tower movements using a film camera. 5

1.4. Film tape elaboration by projection and analytical method. 8

1.5. Trajectory diagrams of tower vibrations and axial torsions of the towers. 12

1.6. Final conclusions. 12

2. PHOTOGRAMMETRIC MEASUREMENTS AND DOCUMENTATION OF A SEA –VESSEL

HULL FOR INSURANCE PURPOSES. 16

2.1. The need to measure vessels. 16

2.2. The Aubacora project – a practical stereo-photogrammetric survey of a fishing vessel. 22

2.3. Discussion and analysis. 26

2.4. Conclusions and recommendations 27

3. THEMATIC MAPPING AND PHOTOGRAMMETRIC MEASUREMENTS OF JOHANNESBURG

AREA, FROM SATELLITE MK-4 CAMERA PHOTOGRAPHS. 30

3.1. Photography for space monitoring systems 30

3.2. MK-4 space photographic camera. 31

3.3. Control and restitiution of the 3D model. 31

3.4. Corrections applied to stereo model. 32

3.5. Conclusions. 33





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1. APPLICATION OF A FILM CAMERA TO HIGH-VARIABILITY

DEFLECTION PHOTOGRAMMETRIC MEASUREMENTS

OF LIGHTING METALLIC TOWERS

The chapter presents a method and results of photogrammetric measurements of high-variability

deflections and axial torsions of 58 m highlighting metallic towers. Film registration was taken with a

16 mm film camera, placed on the tower foundation plate in nearly vertical, constant camera

orientation. The film-tape was measured by projection-graphical method using special review table and by analytical method using a stereo-comparator for measurements of image coordinates and a

computer in transformation to ground coordinates. The trajectories of the tower vibrations were

obtained and axial torsions were computed. The results of the measurements confirmed the experts' thesis that the tower vibrations were caused by the Karman spins. The results of test experiments

referring to the accuracy of the presented method are also reported.

1.1. INTRODUCTION

In the area of dislocation and deformation measurements, the investigations of the dynamic processes, such as high-variability dislocations and deformations of buildings and engineering

constructions, are very important. The object of these investigations is: the control and indication of

danger for buildings showing phenomena caused by excessive dislocation and deformation. The

results of measurements permit to compile suggestions about the building and the related problems. In geomatic practice we have many surveying methods, but for measurements of dynamic

phenomena the photogrammetric methods are especially suitable, particularly those where a speed

film camera is used. These methods are characterized by nearly zero time inertia of measurement and also by the fact that the camera does not touch the measured object because it can be moved away

from the range of influences which can disturb the measurements.

The effect of measurement of dynamic process is most frequently a series of successive positions of the measured object and its state as a deformed body in a given coordinate system and time

function. Comparing the results of measurements taken in time T1 and T2, the trajectory of the process

in time AT= T2 – T1 can be inferred and the changes in geometrical dimensions of the object

measured can be found. In this case, the computations of dislocation and deformation of the measured object in time AT must be performed.

1.2. THE OBJECT OF MEASUREMENTS

Four lighting metallic towers, 58 m high, situated on the sports stadium GTS Vistula in Cracow -

fig. 1.1 - were measured. According to ,,Technical report", after the construction of the towers had been completed, their vibrations of high amplitudes and low frequencies were observed in specific

atmospheric conditions. The vibrations arise when the wind is blowing perpendicularly to the

searchlight part of the tower. These vibrations are transverse, in the plane perpendicular to the wind direction. To be more precise, in the plane perpendicular to the wind direction, the maximum

deflection of the main part of the tower is observed. Since such vibrations can be dangerous for the

tower construction, provisional guy ropes were set up on the four towers on the searchlight level.

According to the experts, the phenomena of wind resonance appear here in connection with Karman's spins, when constant speed air stream flows around the cylindrical rod. High amplitudes of

the construction vibrations cause: a) changes of strength type and increase in stress, which can reach

the limit of admissible values, b) changes of fatiguetesting type of the material structure, which can lead to unexpected fractures without earlier plastic signals. The construction plan of the tower was

designed according to the obligatory contemporary (1967) regulations without any faults. The

limitation of tower vibrations will be realized by:





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1) closing the open part of the tower bowl,

2) setting up special spiral wings to prevent Karman's spins,

3) when searchlights are mounted, the aerodynamic situation will be better because they disturb

the laminar stream of wind.

Fig. 1.1. Lighting tower before searchlights were installed.

The measurements of high-variability movements of the towers had two aims:

a) control of the tower behavior, i.e. signaling of unprofitable phenomena and ascertaining the degree

of efficiency of the protection means,

b) cognitive aim, since the results of measurements will permit to formulate scientific conclusions

with regard to this type of constructions and, consequently, to introduce appropriate

recommendations to building regulations.





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Fig. 1.2. Lighting tower with searchlights.

1.3. PHOTOGRAMMETRIC METHOD OF MEASUREMENTS OF TOWER

MOVEMENTS USING A FILM CAMERA

1.3.1. Adaptation of a film camera

From surveying point of view, a problem of measurements of high-variability dislocations and

dynamic deformations arises. Geomatic methods used for determination of high building deflections

could not be applied because of a big time inertia, both of geomatic instruments and the operator, in

relation to the speed of vibrations and axial torsions of towers.





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A photogrammetric method based on a film camera was devised. It used the film tape for registration. A 16 mm film camera Krasnogorsk was adapted for the measurements - fig. 1.3. The

objective Telemegor 1:5,5/250 mm with the focal length 12,5 times longer than the standard one was

used with the camera. The film in the camera is step transported, frame by frame, by means of a mechanical holder. At the moment of exposition of each frame, the film is motionless and pressed to

the film channel. The tripod head permits to rotate the camera in horizontal plane and tilt it by an angle

over 90°.

Fig. 1.3. Camera with Telemegor lens 1:5,5/250 mm

1.3.2. Distribution of target points on the towers

The shape and dimensions of the target points were selected with a view to obtaining the best

readability on the film. It was found that the most advantageous were target marks with a hole, which

against the sky gave the infallible identification on the film - fig. 1.4. The targets were made of 2 mm

sheet steel. On each tower, the system of targeted marks was installed (towers 1,2 and 3 have three and

tower 4, four target marks). The target points were fastened to the tower trunk at the height of 56 m from the foundations. Inside the tower, a steel ladder is installed, which allows to reach the top of the

tower. All the distances between target points were measured with a steel measuring tape. Extreme

points were located on the average at a distance of 1500 mm. When the towers were equipped with sets of searchlights, they covered the targeted marks - fig. 1.5. Since then, the edges of searchlight-

boxes have been used for observations. The dimensions of these boxes were measured directly and the

edges of the highest (55 m) and lowest (43 m) boxes on each tower were assumed for observation.





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Fig. 1.4. Target mark.

Fig. 1.5. Searchlight on the tower.





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1.3.3. Film registration

The camera station was situated on the foundation plate of the tower - fig. 1.6. Film registration

was taken when the lens axis was nearly vertical and at constant orientation.

Fig. 1.6. Camera on the station.

A speed of wind was measured by the AJ/49 anemometer during whole recording time. Figs 1.7 and 1.8 show enlarged photographs of 16 mm film sections taken with a film camera. Fig. 1.7 presents

the measurements of the fourth tower, where we can see a set of four target points on the level of 56 m

denoted with numbers 1 , 2 , 3 , 4 and also two additional points on the level of 42 m, denoted with

numbers 5 and 6. Fig. 1.8 shows the upper part of the third tower and the numbers 5, 6, 7 and 8 indicate the edges of searchlight boxes assumed as observation points.

1.4. FILM TAPE ELABORATION BY PROJECTION AND ANALYTICAL METHOD.

A special Fenix-Synchro review-table shown on fig. 1.9 and projection-graphical method were

used for preliminary elaboration of the film-tape. This method is based on the projection of individual film frames on the screen situated in such a way that the successive positions of the observed points

can be marked. At the beginning, a sheet of paper with the position of targeted points for the given

tower (in a given scale) is attached to the screen. Then the screen must be set to the position at which

plotted and projected targeted points are adjusted. The screen is kept in this position, and the location of fiducial marks of image plane is drawn on a new sheet of paper. Now each film-frame is projected

and adjusted to the fiducial marks and then the position of targeted points is plotted on the screen. As a

result, a trajectory of the vibration process is obtained. Depending on the density of trajectory points, each film-frame or every, fifth or tenth film frame can be elaborated.





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Fig. 1.7. The enlarged photo of the tower with 6 marks located on levels 56 m and 42 m

The scale 1:10 was chosen, i.e. 1 mm in screen plane corresponded to 10 mm in the plane of

targeted points on the tower. Vibrations of the foundation caused by high-variability deflections of the

tower-body do not affect the stability of the camera orientation. Depending on requirements and

atmospheric conditions, the velocity of screening was: 48, 32 or 24 film-frames per second. ORWO UP 15 and UP 32 films were used. Telemegor 1:5,5/250 mm lens has a satisfactory field of view for

registration of trajectory deflection and gives satisfactorily large scale image.

Simultaneously with screening, the speed of the wind was measured, using AJ-49 anemometer. The station of wind speed V measurement was placed at the central point of sports stadium and the

anemometer was set on a two meter stick. The readings from the anemometer were taken every 15

second and for each minute the average value Vav was computed. The wind speed was measured

several minutes before screening registration and during the registration.





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Fig. 1.8. The enlarged photo of the tower with searchlights boxes.

In one case the wind speed measurements were performed simultaneously at two points: one anemometer was placed as usual at the central point of the sports stadium and the other on the tower,

43 m above the ground level and was set on an arm. The average wind speed on the tower (Vm.T),

taken from 10 minute period, was 2,2m/sec higher than the average on the stadium level (Vav.s). This

value 2,2 m/sec, can be approximately regarded as the local constant of the decrease of wind speed on the ground level in comparison with the speed on the highest level of the tower. The information about

the wind speed was also taken from the State Forecast Office (PIHM) but because of the distance of a

dozen or so kilometers, it had only approximate meaning. To evaluate more precisely the dynamic phenomena of vibrations, the measurements of wind speed should be taken along the tower-body.

The accuracy is characterized by the standard error M0 = 2 cm of the position of trajectory point in

the plane of targeted points.





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The projection-graphical method permits a quick elaboration of a long film-tape. This, in turn makes it possible to select the film and choose the more interesting sections for more accurate but also

more labor consuming analytical process.

Fig. 1.9. Synchro-Fenix review table

The analytical method consists of two stages:

a) the measurements of the image coordinates,

b) computing transformation of the coordinates. The measurements of image coordinates of targeted points and four fiducial marks imaged in the

film channel were made with Zeiss 1818 stereocomparator. Image coordinates u, v were measured using parallax screws p(v) and g(u) — fig. 1.10. Additional telescope allowed to magnify the image to

96 times.

Then, a transformation from the system u, v to ground system x, y was performed. The u, v system is connected with the right stereocomparator carriage (p, q). The axes of x\ y system, on the other

hand, are perpendicular to the optical axis of the camera objective on the camera station, the x, y —

plane being situated on the level of the tower targeted points. Conformal transformation of the first degree was used. Computations were performed using a computer. For computation of transformation

coefficients only two control points are required. When more than two control points were available,

computations of transformations coefficients were made with adjustment. For each film-frame

transformation-coefficients and then x and y coordinates were computed. The standard error of the position of the trajectory point in the plane of targeted points is equal to M0 = 2 mm = 0,009 mm in the

image plane.





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Fig. 1.10. Coordinates measurements with Zeiss 1818 stereocomparator.

1.5. TRAJECTORY DIAGRAMS OF TOWER VIBRATIONS AND AXIAL TORSIONS OF

THE TOWERS

Basing on x, y coordinates, trajectory diagrams of high-variability movements of the towers were

made. On diagrams, the direction and velocity of the wind are shown. Fig. 1.11 illustrates three vibration trajectories of tower No. 4 when provisional guy ropes were set. Fig. 1.12 (tower No. 3)

shows two diagrams of trajectories on two levels: 43 m -inside trajectory and 55 m — outside

trajectory, which were recorded at the same time. To illustrate the regularity of trajectory vibration parameters (fig. 1.13), a diagram of three successive trajectories was drawn. The time interval of

trajectory points for all diagram is 0.125 sec.

Computations of axial torsions were made for vibrations with higher amplitudes of deflections. The maximum values of axial torsions were up to 1 degree 56 minute angle.

1.6. FINAL CONCLUSIONS

1) The measurements confirmed the experts' thesis that vibrations of the towers were caused by

Karman's spins. 2) The presented method of photogrammetric measurement of tower movements permits a

simultaneous recording of movements on several tower levels and a calculation of the tower axial torsions.

3) This method may find wide application in the investigations of high-variability processes in engineering measurements





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Fig. 1.11. Trajectories of tower vibrations on the level of 56 m with provisional guy ropes.





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Fig. 1.12. Trajectories without guy ropes.





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Fig. 1.13. Three successive trajectories on the level of 55 m.





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2. PHOTOGRAMMETRIC MEASUREMENTS

AND DOCUMENTATION OF A SEA-VESSEL HULL

FOR INSURANCE PURPOSES

This chapter investigates the usefulness and applicability of close-range photogrammetry to the

marine industry, not only from a technical point of view, but also regarding classification, registration and insurance aspects as well. It is suggested that close-range photogrammetry, performed during

routine marine surveys of a vessel hull, provides valuable technical information which is essential to

the marine underwriter. In particular, the use of stereo-photogrammetric documentation methods which provide reliable stereoscopic three-dimensional interpretation and measurements, is strongly

suggested to marine underwriters.

The shipping industry, the world over-relies on marine insurance for peace of mind. While safe

passage of goods or people can never be fully guaranteed, the underwriter pledges to cover the

specified risks involved, and thereby minimizes the losses incurred in the event of a marine accident.

Research shows that sound technical evaluations of vessels are desired by underwriters, as a basis upon which to make sound actuarial decisions. How else should an underwriter compute the risk

associated with insuring a vessel, other than with reliable and verifiable documentation?

A practical photogrammetric survey, of a fishing vessel hull has been carried out at Cape Town’s

Waterfront Synchro-lift, using metric and non-metric cameras. Results indicate that stereo-

photogrammetric documentation is able to record vessel details such as rust patches, weld lines, etc., to 5mm accuracy, with respect to the vessel itself. Stereo-photogrammetric measurements were

processed to digital, three-dimensional co-ordinate format. Provided that one has the appropriate

software, any form of data visualization is then possible as surface models, plan views or cross-sections.

Stereo-photogrammetric documentation is found to be highly appropriate for supplying the marine

underwriter with sound technical information on vessel hulls by providing: visual, remotely sensed, permanent, storage-efficient, and archival information which is independently verifiable.

2.1. THE NEED TO MEASURE VESSELS

Firstly, let us answer the question - Why is there a need to measure and document the

characteristics of a given vessel? - from global and local perspectives. The maritime community's desire to define, measure, and record the size of a vessel, particularly its internal cargo-carrying

capacity, has been apparent as long as there have been merchant ships engaged in international trade

[Surveyor 1994 Dec.]. Systems of 'tonnage' have been particularly important, records of which date

back long before the Christian era. Such systems have tried to standardize the quantifying of a vessel's internal volume, i.e. its net tonnage, in order to estimate that vessel's earning capability (cargo). Other

systems determine gross tonnage, used to calculate things such as port duties, premiums with

underwriting bodies, and dock dues [Surveyor 1993 Dec.; p.30].

Most maritime countries have legislation designed to regulate shipping activities, with the overall

focus being on safety at sea. In South Africa, the Merchant Shipping Act, No. 57 of 1951, fulfils this

purpose. The Act requires every vessel of 25 or more gross tons, owned or operated by a South African citizen or concern, to have its particulars entered in an official register [Ch.2, Sec. 10 & 13].

Registration at a gazette “Port of Registry” must be preceded by a marine survey, so as to ascertain the

tonnage of the vessel [Ch.2 Sec.16]. Details of the vessel's dimensions must also accompany registration [Ch.2 Sec.20].





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Further to these requirements, any ship registered in RSA which is greater than or equal to 14m in

length, and is not solely engaged in fishing or yachting, must have a Load Line Certificate (LLC).

Such a certificate attests that the 'load line ship' has been surveyed, and that the vessel's hull has been marked to reflect the maximum depths to which that vessel may be loaded for various sea conditions.

The salient point here is that a load line ship must be thoroughly surveyed prior to her being put into

service, and subsequently at intervals not exceeding five years [Article 14 a & b]. This brief outline of the areas where marine surveys are performed is intended to emphasize the market demand for such

work.

2.1.1. MARINE INSURANCE

It should be apparent to the reader that the motivation behind the conventions and legislation, and

therefore the marine surveys, is the safeguarding of lives, interests, and capital assets in the shipping industry. However, since no ship's passage is guaranteably without incident or mishap, the 'parties to a

marine adventure' have found it necessary to protect themselves from unfortunate losses. The role of

the marine underwriter is thus created. Marine insurance is designed to minimize the financial

damages sustained in a maritime accident, it is not however compulsory. In return for relative peace of mind, a vessel operator or owner will pay an insurance company a premium. The cost of insurance

depends directly on the risk that the insurance company associates with the policyholder's vessel.

There are two kinds of marine insurance: property insurance and liability insurance. The ship-owner or operator's liability insurance is essentially protection and indemnity (P&I)

coverage. Marine property insurance concerns the insurance of cargo and hulls, the latter being of

particular relevance to this project. Hull insurance covers all the vessel's equipment and structures, as well as liability for damage to another vessel, in the event of collision. Nick Blenkly, in the

September 1991 issue of SURVEYOR [p.22], reports that there has of late been an increase in the

number of large insurance claim settlements. Consequently, insurance market 'capacity' has shrunk; it

is a simple matter of economics that ship-owners are now having to pay substantially higher premiums. However, Blenkly goes on to add that there is a positive aspect to a pressurized marine

insurance market. He makes the significant suggestion, that it would be easier for insurers to guarantee

peace of mind if they could place more emphasis on sound, technical appraisals of the risks they are covering. To summarize: "... in such a market, the ship-owner with a good insurance record is less

likely, in the long term, to find himself subsidizing less careful operators". Marine insurers specialize

in risk assessment, not in technical investigations. Consequently, if a ship-owner is to enjoy discounted insurance premiums resulting from his vessel being of sound construction and well

maintained, he requires a more comprehensive marine survey than that afforded by adhering to

minimum legislation.

Geoff Broad, from the Technical Services Division of insurance company First Bowring and Associates in Johannesburg, has explained [BROAD, 1994], that "there has been a major push by

underwriters in the last few years to 'clean up' the seas of the sort of vessels that have been seen

around the Cape recently... They [underwriters] have utilized the [marine] surveyors of Classification Societies to do this, and annual surveys are an underwriting requisite of oil tankers over a certain age,

for instance. Any method that saves costs and is easier to perform for this increasing volume of

surveys could therefore be very beneficial.".

2.1.2. CLASSIFICATION SOCIETIES

Classification Societies are non-governmental companies offering a wide range of inspection and validation services to ship owners and operators alike. At present there are 42 Classification Societies

operating world-wide [STD-BUL, 1994]. In the normal course of events on a deep sea vessel,

insurance will not be considered unless the vessel is in possession of full, current Classification





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Society Certificates of Class for Hull, Machinery, Automation, and Special Features… [MATHESON, 1994]. It should be noted that classification, as such, has no legal status, although a ship not certified

as ‘in class’ by a reputable Society is unlikely to obtain insurance or employment [GUY, 1989; p.105].

Right from their origins, the primary function of Classification Societies was to provide marine underwriters with information describing the actual condition of vessels insured [B.V., 1989; 7].

Fig. 2.1. Marine Casualties.

Nowadays, the vast majority of shipping communities firmly support the concept of classed ships; merchant vessels designed, built, and maintained to the high technical standards established and

administered by Classification Societies [B.V., 1989; p.7]. Moreover, a very commonplace proviso in

marine insurance contracts is a clause which warrants that the vessel insured be kept ‘in class’ throughout her period of entry on the underwriter’s books. Apart from classification, the technical

services offered by Classification Societies may include, for instance, naval architecture,

hydrodynamics, structural analysis, and vibration analysis [B.V., 1989; p.29].

2.1.3. SHIP CONSTRUCTION, ALTERATION, AND DIMENSIONAL CONTROL

Prior to exploring the topic of marine surveys it is necessary to understand something about the construction of vessels themselves. The curves delineating a vessel's hull are generally not

mathematical expressions, and it is therefore necessary to have a 'lines plan' which will depict (in as

detailed a manner as possible) this surface of the ship [TAYLOR, 1987; p.33]. The lines plan consists of three drawings which show three sets of sections [TAYLOR, 1987; p.35]. Each of three mutually

orthogonal planes gives a different plan: body plan (planes perpendicular to the vessel centerline);

waterlines or level lines (horizontal planes parallel to the vessel base); and sheer profile or buttocks

(vertical planes parallel to the vessel centerline). Many other detail plans are required during construction, but these will all be based upon the 'principal dimensions' of length, depth, and breadth

[TAYLOR, 1987; p.26].

Ships are usually built into jigs, which are preassembled to represent the design dimensions as best

as possible. The individual metal sheets are then bent, rolled, or beaten to conform to the jig

structures; the vessel often goes 'out of design' at this stage [TAGGART, 1980]. Methods of





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dimensional control, and associated tolerances, are influenced by the following assembly and fabrication considerations [TAGGART, 1980; p.629]:

structural acceptability - in accordance with regulations of a particular agency;

operational acceptability - to satisfy the client's special requirements; fabrication requirements of the shipyard - emphasis on cost-effectiveness.

It would appear that while standard tolerances for construction are desirable, what is more relevant to

the shipbuilder are tolerance limits. Such limits should come from Classification Societies, based on input from research, industry, and service experience [TAGGART, 1980; p.630]. The matter of

acceptable tolerances depends largely on the stress condition of the fabrication material, the location in

the ship, and the judgment of the marine surveyor.

Dimensional control methods for fabrication and assembly are essentially the same as those used in

subsequent marine surveys, as well as in the alteration or modernization of vessels. These include the

use of calibrated steel tapes, set-squares or 3-4-5 tape triangulation, while level planes are determined using elementary hydrostatic levelling - the water tube method [TAGGART, 1980; p.630]. Piano wire

is used for aligning over short distances, whereas theodolites and lasers are used for aligning major

components such as keel blocks and shafts.

Close-range photogrammetry in the ship building industry has been successfully used in the United States [KENEFICK, 1977] as well as European countries, for point-by-point assembly control.

2.1.4. MARINE SURVEYS

The marine survey is an inspection, recording and measurement process relating to a ship. Marine

surveyors do not normally require any special marine qualification, although the majority will possess a marine background [GUY, 1989; p.2]. The purpose of any statutory or class survey is to be able to

provide the ship with a document certifying its compliance with certain standards. In many cases the

Classification Societies have assumed the role of government agencies, carrying out the requisite

surveys and issuing international certification on behalf of the administration [GUY, 1989; p.105]. If a vessel is not classed, she will nonetheless have to satisfy minimum standards of strength, and will

undergo similar surveys to a classed vessel. These classification surveys are listed below [KEMP &

YOUNG, 1989; p.4] : Annual Survey;

Docking Survey - every 12 to 24 months;

Special Surveys - every four years, increasingly severe with age of vessel. In addition, any time there is an insurance claim against the vessel, a survey of the relevant aspects

of that vessel will take place [TAGGART, 1980]. All hull deformations and distortions, systematic or

otherwise, inherent or unnatural, have implications for any measuring or recording methodologies

used in a survey of a ship. Measurements in the field are made using steel tapes and battens in an offset method. The reliability of any measurement in a marine survey thus depends on the past history

of the plate or assembly involved in that measurement.

2.1.5. SUPERIOR APPLICABILITY OF STEREO-PHOTOGRAMMETRIC SURVEYS

A documentation survey is a general survey of a structure, the final application of which are not

exactly known a priori, although the surveyor has a good understanding of the scope of his client's future requirements. The writers believe that vessel-hull documentation, for non-specific insurance

purposes, is best performed using stereo-photogrammetric methods, for the following reasons

concerning: 1) Cost,

2) Time,

3) Legal and Archival Factors of Stereo-Photogrammetric Surveys.





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Perhaps the most considerable advantage of stereo-photogrammetric documentation surveys is the ability to explore the subject of photography in three dimensions. This aspect of stereo-interpretation

plays a key role in these surveys and allows the observer to discern between object features which

might well be indistinct on a single plane photograph while measured monoscopically.

If a stereo-photogrammetric survey of a vessel hull is carried out while a vessel is in dry-dock

condition, the work may be performed in the background, so to speak, with minimal disruption to routine operations. Such conditions enable the docking period to be more cost-effectively used.

Photography in itself is a rapid process. The primary limitation on speed of operation is the bulkiness -

or otherwise - of the camera equipment used, and the size of the vessel to be photographed.

Insofar as a comprehensive stereo-photographic record of a hull permits the entire hull to be

explored in three dimensions, the greatest benefit is obtained if that survey forms part of a series of

surveys performed over the course of time. Deformation - depending on the level of precision required - may be detected and monitored. Photogrammetry can also be useful for recording and

measurement of dynamic deformations of a vessel hull during a launching [FLOREK, 1975, p.88-94].

Features or parts of the vessel hull (or even the superstructure), which find themselves the subject of a legal/insurance dispute between two or more parties, can be visually scrutinized in a fully

restituted three dimensional environment. Furthermore, should the need arise to quantify damage,

measurements can performed to a degree of precision surpassing that of traditional marine survey measurements. The photographs comprising a photogrammetric survey therefore represent compact

and efficient databases, the contents of any part of which may be independently examined by objective

experts in the field of photogrammetry.

2.1.6. INSTRUMENTATION AND METHODOLOGY FOR STEREO-SURVEYS

The primary categories of cameras encountered in close-range photogrammetry are metric and non-metric photographic and digital CCD (Charge Coupled Device) cameras. Metric photographic

cameras usually have the following features:

1) precisely designed and calibrated; 2) known, stable interior orientation;

3) often fixed focus;

4) contain fiducial marks or reference grid for inner orientation purposes; 5) contain film flattening devices or allow glass plates;

6) relatively expensive.

An example of such camera is the Zeiss UMK 10/1318, used in this practical test project described

presently. Fitted with four fiducial marks, and taking single cut-film cartridges, this camera is currently priced at USD 20k [HON, 1994].

Non-metric cameras are often termed 'amateur' cameras, and usually have the following features:

a) usually hand-held; b) unstable interior orientation;

c) non-rigid construction - variable focus;

d) no fiducial marks;

e) lens design often sacrifices geometry for image resolution; f) relatively inexpensive and widely available.

A Mamiya C330, costing approximately in the region of USD 4k [HON, 1994], was also made use of

in the test survey. This camera can be equipped with a reference grid glass plate for additional cost of USD 500.





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Fig. 2.2. Mamiya C330 and Zeiss UMK 10/1318 cameras.

The latest sample Kodak, Nikon, Canon CCD cameras, available on commercial market, represent following features:

one image is composed of about 24 megapixels of data;

storage capacity on memory cards – depends on card capacity – up to 4k photos;

28mm CCD lens acting as 70mm (regarding bundle angle); battery operated;

full self-calibration necessary to estimate image geometry and stability;

CCD camera costs approximately USD 5k. A one pixel resolution of this camera equipped with Nikon 28mm lens is approximately 1 mm at 10m camera-to-subject distance, which is about 10 times

less than for the UMK using glass plates. This equates approximately with 10 times decrease in

resolution to the UMK using glass plates. However, rapid progress in the development of CCD

technology promises that higher resolution cameras will be available soon. The ADAM-Topocart analytical stereo-restitutor conversion used in processing the test survey is an

example of a stereo-restitutor, where x, y operator control forms the user input into the computer-

controlled restitutor. Additionally, the operator removes horizontal parallax p with the 'z wheel'. Analytical stereo-restitutors permit continuous measurement as they operate under computer control,

restoring the stereo-model in 'real time'. Stored orientation parameters and systematic model

correction data are then used to generate q parallax carriage translations, which preserve the stereomodel free from vertical parallax q for the viewer. All x, y instrument co-ordinates are

automatically transformed to object co-ordinates, using stored interior and exterior information. The

resolution of the ADAM measuring system is one micrometer. The ADAM-Topocart conversion kit

from the older Zeiss-Jena analogue 23x23cm format stereo-restitutor costs approximately USD 35k; while the newer technology full 23 x 23cm format analytical stereo-restitutor ADAM Promap by the

same firm costs USD 50k.

Other forms of modern stereo-restitutor, falling into a cheaper category of equipment, include such

devices as Leica's Digital Video Plotter "DVP". However, DVP does not contain any plotter build in,





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so, from design concept point of view, should be named as a digital video stereo-restitutor. DVP fulfils two essential functions of stereo-restituting and stereo-digitising of a real 3D oriented model,

which are attributes of stereo-restitutor. Therefore, DVP is essentially a digital image-based stereo-

video-restitutor, which might serve as an inexpensive substitute for the ADAM-Topocart or others, especially when used directly with digitally captured images on CCD camera.

Fig. 2.3. ADAM-Topocart analytical stereo-restitutor.

2.2. THE AUBACORA PROJECT - A PRACTICAL STEREO-PHOTOGRAMMETRIC

SURVEY OF A FISHING VESSEL

In order to evaluate the practicalities of a stereo-photogrammetric vessel surveys, it was necessary

to carry out, at least in part, the photogrammetric documentation of a vessel. While ships of overall length 20 to 50m were considered suitable for such a project, the issue of physical accessibility was an

important parameter. This latter constraint brought to bear on the location of the vessel during the

survey. A choice was therefore made between one of two sites on the Cape Town Waterfront:

Robinson Dry Dock (supporting vessels longer than 100m), and the specialized shunting system called a synchro lift (using which, lighter and shorter vessels may be hauled out of the water, and onto dry

land). When it was learned that the fishing vessel Aubacora, belonging to Tri-Ocean Marine, was

available for a minimum period of ten days on Lane 3 of the synchro lift, it was decided to mobilize.

A reconnaissance survey was first made of the general working area at the synchro lift. This

entailed taping distances between adjacent lanes, so as to determine the maximum subject distance available (typically 5 to 7 meters) for taking the photographs at a later date. A strip of recce

photographs of the Aubacora, taken with a hand held Ricoh KR5 Super with 55mm lens, were used

later to plan the location of control targets. The reconnaissance survey, which included general

familiarization with the work site, took some two hours.





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Fig. 2.4. Diagram of ADAM-Topocart analytical stereo-restitutor.

2.2.1. Co-ordinate Systems Used in the Aubacora Project

Fig. 2.5 illustrates the several co-ordinate systems encountered in the Aubacora project. Three

principal co-ordinate systems are distinguishable: the theodolite observation system; local survey control system; and the vessel reference system used in stereo-restitution. The survey system was

chosen simply as a three dimensional, left-handed system, with the direction of the Z axis coinciding

with the local direction of gravity. All theodolite observations were made in this context; subsequent network adjustments took place in the same system. A right handed local system adopted S9 as the

origin, with S0 constrained to lie on the positive X-axis. In order for the theodolite observations to be

correctly processed by the intersection program used, the left-handed horizontal observations had to be

transformed into this co-ordinate system. The ADAM-Topocart stereo-restitutor requires the three-dimensional object (vessel) co-ordinate system to be right-handed, with the positive Z axis extending

toward the camera station. In this case, the origin of the system was made to coincide with the vessel

target AFT-RUD, situated at the aft rudder post. The positive X axis was constrained to pass through the target FWD-L, the lower, forehead-most hull target.

2.2.2. Establishing the Control

A series of ten theodolite stations was coordinated in a local trilateration network surrounding the

Aubacora. A Wild TC 1000 Total Station (single second), and a single prism, were used for all the

observations. Final 2D (Y,X) co-ordinates were obtained in the left-hand theodolite observation system by performing a least squares trilateration adjustment; S9 was treated as the origin, and S0 was

constrained to lie on the negative X axis. The stations finally used in the control net were heighted





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separately and reciprocally , giving a final disclosure of 1mm, and standard deviations of a final mean height varying from 1 to 3mm.

Fig. 2.5. Diagram of photogrammetric coordinate system.

The use of analytical stereo-photogrammetry and -restitution methods required individual stereomodels to be oriented 'absolutely', i.e. within a fixed object control system, by means of a

minimum of four X Y Z coordinated targets. As an empirical check on the calculation, several chalk

marks were made along the hull so as to demarcate the physical limits of UMK and Mamiya

photographs, using their respective viewfinders. Each photo was to contain six control points in the stereo pair in order to ensure that each photograph in the strip formed part of two models and still

enjoyed a sensible overlap. Using a 'footprint' of 10.8 m, this would mean that the interval between

target pairs would have to be nominally 5m.

A set of targets was made consisting of a 100 x 100mm black paper background, onto which a

white dot was stuck, approximately 25mm in diameter. This was in turn stuck to the back of a section of clear adhesive film; the film was then pressed to the ship's side. A small square of double sided

tape, directly behind the dot, assisted with the adhesion. In addition to these targets, rigid plywood

targets (black background with white dot, as before) were used to identify certain features. Such

features included FWD-U and FWD-L, the two forehead upper and lower points on the ship's stem; and AFT-RUD, a point on the rudder post, right aft. These three points were later used as 'hard' points

in the transformation from ground control co-ordinates to the ADAM-Topocart's object co-ordinate

system. This latter target design was very satisfactory in terms of adhesion and clarity. BROWN (1984) suggests a much smaller white dot diameter of approximately 6mm in order to produce a 60

micrometer diameter point in the stereomodel (at 10m subject distance and 90mm PD.). However,

FLOREK (1994) is in favor of the diagonal, black and white type of target, because of its effectiveness regardless of photo scale. Application of the targets was straightforward. The total time taken to

apply all 16 port targets, including annotating the hull with the target names in chalk, was

approximately 50 minutes.





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2.2.3. Coordinating the Hull Targets

Both faces of the theodolite were read for horizontal and vertical observations, with the mean taken

for each. This meaning procedure was of particular importance owing to some of the steep vertical angles measured; the effects of collimation axis error, horizontal axis error, and vertical circle index

error being thereby negated. Horizontal directions were referenced to the network itself. That is, one

or more (up to three) orientation directions were observed, ending on a single R.O. In this manner, each target was intersected by two rays or very occasionally three. The port side reduced observations

and corresponding observation station co-ordinates were processed by an intersection program

designed by Mr G. van der Vlugt from the Department of Surveying and Geodetic Engineering,

University of Cape Town. Precision estimates for X,Y co-ordinates were naturally not available for two-ray intersections, but RMS errors were estimated from error theory to be about 5mm.

2.2.4. Photography

A metric Zeiss UMK 10/1318 camera was used with Ilford cut film to take photographs of the

entire port side of the vessel. To investigate the suitability of non-metric cameras for documenting a

vessel hull, it was decided to also take photographs with a non-metric Mamiya C330 camera, calibrated by ADAMS (1980). The Mamiya used Fujichrome ASA 100 color slide film. Prior to any

photography taking place, suitable locations for each camera station were marked on the ground, to

within approximately 0.5 m. These stations were decided on by inspection, using the viewfinders of the UMK and Mamiya cameras. Typical subject distances for the UMK and Mamiya were 8 and 18m

respectively. Calculations for depth of field, coupled with light meter readings, prescribed the use of

1/32 f-stop and 1/4 second camera settings for the UMK. The Mamiya photographic work, performed the next day, used similar settings. Ten UMK exposures were made of the Aubacora's port side, from

eight camera stations. The UMK was mounted on a survey tripod, approximately levelled and

nominally oriented at right angles to and tilted 15 degrees upwards from the horizontal. Final

exposures were taken once it was ascertained that all three vertical pairs of control targets were in view. A similar procedure was followed for the Mamiya photographs, albeit from different stations.

On account of the bulky equipment associated with the UMK camera, the port side photography took

approximately three hours to complete; the Mamiya photography was completed within fifty minutes.

2.2.5. Stereo-processing on the ADAM-Topocart Analytical Stereo restitutor

Model Name A4A5UMK MAM11-12 A5B6UMK MAM10-11

Camera used UMK Mamiya UMK Mamiya

Photo pair A4, A5 11,12 A5, B6 10-11

Film make Ilford Fujichrome Ilford Fujichrome

Film speed ASA 110 ASA 100 ASA 110 ASA 100

Film type b&w colour-dia b&w colour-dia

Subject distance 8 m 18 m 8 m 18 m

Effective P.D. 100.35mm 83.00mm 100.35mm 83.00mm

Photo format 166x119mm 57x56mm 166x119mm 57x56mm

Photo Scale 1:130 1:220 1:130 1:220

# Control points 4 6 4 6

# Pass points 3 3 4 2

X RMS [mm] 3 5 1 12

Y RMS [mm] 3 6 2 12

Z RMS [mm] 4 16 2 33

Tab. 2.1 - The final orientation results from the ADAM-Topocart for all four models





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Two stereomodels from each of the UMK and Mamiya sets of photographs were restituted on the ADAM-Topocart. In order for the ADAM-Topocart measurements to be meaningful with respect to

the vessel itself, the hull targets, coordinated in the local survey system, had to be transformed. The

ADAM-Topocart orientations were carried out with the relative/absolute exterior parameters being computed automatically and simultaneously, using a bundle adjustment. The final interior and

exterior orientation results for all four models are given in the accompanying Tab. 1 Once the models

had been oriented, a Feature Code list was set up to aid digitising. The following hull features were identified and digitized in full XYZ co-ordinates:

hull features (pipes, hatches, etc.)

rust patches;

weld lines; control targets;

spot shots

damage areas. A sample of each of these feature types was captured using the ADAM-Topocart's ASCII digitising

data format.

Fig. 2.6. UMK photo of a ship

2.3. DISCUSSION AND ANALYSIS

The literature reveals a strong need for independently verifiable, technical information, concerning

the dimensions and structural integrity of vessels in general. Classification Societies, independent Marine Surveyors, and certain government bodies, exist in the maritime environment for this very

reason. While some of their methods of measurement and investigation may seem crude, it should be





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borne in mind that the question of a vessel's seaworthiness may often be resolved by simple inspection. Moreover, mensuration is often carried out at levels of precision consistent with vessel

fabrication. Nonetheless, marine underwriting bodies have clearly expressed the desire for more

verifiable, reliable information concerning a vessel's condition. This concern is expressed in particular for older vessels.

A stereo-photogrammetric survey of a vessel hull performed in a dry dock condition should have a well-established control net, observed without the hindrance of obscuring vessels. The surveyor can

then choose suitable theodolite observation points from which to fix the hull control. Inadequately

fixed, or distorted hull control, will introduce Y-parallax into the related stereo-model. This, in turn,

results in inaccurate X,Y,Z co-ordinates for measured model points.

While in this project the Mamiya camera was considerably faster to deploy on site than the UMK,

an experienced operator might narrow the time difference considerably. It is therefore not advisable to make inferences based on deployment time alone. However, it must be borne in mind that the full

complement of UMK equipment is over ten times as heavy as the Mamiya camera itself. At a camera

station with restricted movement; on a working site busy with traffic; or between brief periods of

sandblasting, rapid camera deployment is a distinct advantage. The RMS errors of X,Y,Z co-ordinates for an exterior orientation are directly related to the accuracy of observed control targets. In a stereo-

model, this accuracy can be interpolated to any other well-defined point, observed within the limits of

the model control. The practical proof of this statement is the visual comparison of general q-parallax in the stereo-model, before and after the introduction of 'absolute' control. If there is no discernible q-

parallax at any point in the model after relative orientation, the introduction of an accurately co-

ordinated set of control points should not change this situation. Y-Parallax problems will thus be traceable to poor control, or poorly observed points. In this regard, all the UMK stereomodels were

well oriented. The orientation results of the Mamiya cameras, when compared with UMK results, are

also very favourable. An increase in RMSe values for Z, compared to their X,Y counterparts, is the

result of an insufficiently accurate Mamiya Principal Distance PD value, used in the restitution calculations. Stereo-digitised in full 3D format are immediately ready for further processing on any

appropriate CAD package. An example of the stereo-digitised model, plotted from a CAD package

may be found in Fig. 2.

2.4. CONCLUSIONS AND RECOMMENDATIONS

The test survey carried out on Aubacora, as well as the literature researched and explored, permit

the following conclusions and recommendations to be drawn. These conclusions support the use of

stereo-photogrammetry in vessel hull documentation survey for non-specific insurance purposes.

2.4.1. Conclusions

1) There is a need for technical survey documentation of marine vessels. The marine insurance industry relies on sound technical information in order to make realistic actuarial assessments

of insured hulls.

2) Photogrammetric methods are suited to vessel hull documentation. Photogrammetric records

(photographs or digital images) represent databases of great detail; they are compact, permanent and make economical archives. The information contained within the vessel

photographs may be independently verified, at any future date.

3) Stereo-photogrammetric documentation is highly applicable to vessel surveys. A documentation survey provides a general survey of a structure, the final applications of which

are not exactly known a priori, although the surveyor has a good understanding of the scope of

his client's future requirements. Reliability and precision of stereo-photogrammetric survey





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methods is higher than that of the original vessel construction control, and is therefore acceptable.

4) Non-metric analogue and CCD cameras are suitably accurate substitutes for metric analogue

or digital CCD cameras. Provided the non-metric camera is well calibrated for a working subject distance, such a camera may be successfully used for stereo-photogrammetric

documentation of a vessel hull. However, the non-metric camera has to be fully calibrated or

self-calibrated in order to be a sufficiently reliable instrument.

5) Stereo-photogrammetric vessel documentation using Black & White film assists in feature

definition. B&W film, and in particular using B&W negatives, allows the stereo viewer to

discern fine hull features, which are difficult to perceive using colour film.

6) CCD cameras provide fully digital stereo-photogrammetric processing. Rapid progress in the development of CCD cameras promises that these cameras, being laboratory tested with

resolution above 24 megapixels, are available on commercial markets. Thus digital video

stereo-photogrammetry will be better applicable for precise engineering surveying.

2.4.2. Recommendations

a) Marine underwriters should compel underwritten vessels to undergo periodic photogrammetric surveys. The period during which a vessel is compelled to dry dock,

typically for statutory or classification marine surveys, it can be productively used; a

photogrammetric survey of the hull ought to be undertaken for insurance documentation purposes. Photogrammetric surveys should therefore be performed every four or five years,

beginning immediately after construction, and prior to launching. The photographs will be a

historical record of the insured vessel's service life and physical condition. b) A photogrammetric vessel survey should use stereoscopic methods. Any part of the vessel

hull, recorded in the photographs of a stereomodel, may be stereoscopically restituted at any

future date. No prior specification of the features to be measured is required at the

photographing stage, this criterion being essential for a documentation survey. Stereoscopy will assist in interpreting vessel features by recreating the perception of depth, and is thus

recommended.

c) Non-metric cameras, well calibrated for a working subject distance, should be used to perform stereo-photogrammetric vessel surveys. The expense of full-blown metric cameras can be

obviated by using non-metric cameras, providing that calibration is performed at an

appropriate subject distance for vessel surveys. d) Stereo-photogrammetric documentation surveys should principally make use of Black &

White film. B&W negatives will enhance the interpretative aspect of the photographic

documentation. Experimentation with other types of film, such as B&W infra-red, might

prove successful in recording subtle or invisible details. Simple colour photographs of deck spaces and superstructure can broaden the scope of the survey.

e) CCD cameras should be considered as a tool for vessel hull stereo-documentation. Maturation

of CCD camera technology and availability of digital video stereo-restitutors will ultimately enhance the Engineering Surveyors' repertoire of measurement tools. CCD cameras will then

find useful application in vessel hull stereo-documentation surveys for marine insurance

purposes.

REFERENCES

ABS. 1994: "New Ideas For Existing Hulls", Special Publication by American Bureau of Shipping





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ADAMS LP. 1980: "The Use of Non-metric Cameras in Short Range Photogrammetry", Archives of 14th ISP Congress, Hamburg

BROAD G. 1994: Correspondence with the writer by facsimile, September

BROWN DC. 1984: "Close Range Photogrammetry and Surveying - State of the Art", Workshop Proceedings,

ASPRS

BV. 1989: "What is a Classification Society ?", Special Publication by Bureau Veritas Courbevoie

FLOREK R. 1975. "Możliwości pomiarów szybkozmiennych odkształceń kadłubów morskich statków metodą

fotogrametrii", (Possibilities of Deformation Measurements of the Sea Vessel-hulls using

Photogrammetry). In: Materiały Konferencji SGP "Geodezja w gospodarce morskiej", Gdansk,

Poland, pp.88-83

FLOREK R. 1988: "Improvement of Photogrammetric Methods Used for Constructing, Mounting, and

Exploitation of Engineering Structures", (in Russian). Materialy Konferencji Specjalistow Sluzb

Geodezyjnych KS nt. "Automatyzacja prac geodezyjno- inzynierskich", IGiK, Jadwisin-Warsaw,

Poland, pp.1-57. GOWANS B. 1994: Interviewed by the writer at Maritime & Industrial Services Head Office, on 30 June 1994

GUY J. 1989: "Marine Surveying & Consultancy", Fairplay Publications HON J. 1994: Correspondence with the writer by facsimile, August

KEMP JF. & YOUNG P. 1989: "Ship Construction Sketches and Notes", 3rd Ed., Heinemann Newnes

KENEFICK JF. 1977: "Applications of Photogrammetry in Shipbuilding", Photogrammetric Engineering &

Remote Sensing, September

LENZ R, BEUTLHAUSER, & LENZ U. 1994: "A Microscan/Macroscan 3x12 Bit Digital Color CCD Camera

with Programmable Resolution up to 20 992 x 20 480 Picture Elements". Proceedings of the

Commission V Symposium - Close Range Photogrammetry and Machine Vision, International

Archives of Photogrammetry and Remote Sensing, Vol.XXX, Part 5, pp.225-230

MATHESON HDM. 1994: Correspondence with the Author on 25 July and interview

OLIVER PRF. 1994 "Close-range Photogrammetry of a Ship's Hull - Implications for Marine Insurance". B.Sc.

(Hons.) Surveying Thesis, University of Cape Town

STAMPA HR. 1980: "The Development & Testing of.. using the Mamiya C330F Cameras in Short-range Photogrammetry", B.Sc. (Hons.) Surveying Thesis, University of Cape Town

STD. BUL. 1994: "Classification of Ships", The Standard Bulletin, Issue 22, May, p.4

STIRLING DM. 1990: "Close-range Photogrammetry", Engineering Surveying Technology, Chapter 8, Blackie

TARGGART R. 1980: "Ship Design and Construction", The Society of Naval Architects and Marine Engineers,

New York

TAYLOR DA. 1987: "Muckle's Naval Architecture", 2nd Ed, Butterworths

THOMSON MM. 1980: "Manual of Photogrammetry", American Society of Photogrammetry, 4th Ed., Virginia





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3. THEMATIC MAPPING AND PHOTOGRAMMETRIC

MEASUREMENTS OF JOHANNESBURG AREA,

FROM SATELLITE MK-4 CAMERA PHOTOGRAPHS

This chapter sets out the results of investigations and practical tests of stereo restitution and stereo

digitizing of a 3D-model produced from 1:890,000 Russian space photographs of the Johannesburg

area, South Africa. The photographs were taken using a MK-4 space photographic camera with a size of 180mm x 180mm, a principal distance of 300mm and a flying height of 268km.

The MK-4 camera consists of four lenses and can be used as a multispectral. A three layer color spectrozonal film can also be applied for ready IR false color compositions in the range of 580-800

nanometers. The stereorestitutor was calibrated to glass rectification plates (size 230mm x 230mm)

with a 10mm grid. The stereomodel was oriented and corrected with regard to the following model

disturbances: 1. Film deformations;

2. Symmetric radial distortion;

3. Atmospheric refraction; 4. Earth curvature.

The ground control points were taken from a 1:10,000 orthophoto map. Many different features

were examined as possible reference points for model scaling and external absolute orientation. These features include: road intersections, corners of fields and houses, tree lines, rivers and canals. Different

combinations of control points were applied for absolute orientation. The best results were achieved

using eleven control points with RMS errors of approximately 8 meters on the ground.

The important component of photointerpretation was applied in order to provide control points and

to later aid in the stereo digitization of the corrected and oriented model. A sample of a land-use thematic map of a chosen area was then produced. The conclusions and recommendations obtained

from these investigations may be useful for potential users of satellite photographs for thematic

mapping.

3.1. PHOTOGRAPHY FOR SPACE MONITORING SYSTEMS

The practical aspect of this report involves the stereo restitution of a pair of Russian space photographs of the scale 1:890,000 on an analytical stereo restitutor to form a corrected three

dimensional (3D) model. Photographic emulsions which are applicable to monitoring systems can be

classified as follows: one layer Black and White; one layer Infrared Black & White;

three layer Color;

multilayer Spectrozonal.

The sensitivity of a multilayer spectrozonal emulsion extends into the infrared region. One layer is sensitive to infrared radiation and the other layers are sensitive to different regions within the visible

spectrum. The final image is in false color and can be used for photo-interpretation, thematic and

topographic mapping and other geomatics processing. Owing to the advances in the operational capabilities of sensor platforms and the development of fine grained, high resolution photographic

emulsion, most camera systems now include not only fiducial marks or reference grids, but image

forward and angular motion compensation devices as well.

Satellite photographs can help generate thematic and topographic maps in medium (about 1:25,000

- 1:50,000) and small ( =< 1:100,000) scales much quicker and cheaper than conventional methods.

This is of particular advantage to developing countries. Satellite photography should be viewed as





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being complementary rather than competitive to the electro-optical monitoring systems like LANDSAT and SPOT.

1. In order to fulfil mapping requirements at 1:100,000 and 1:25,000 scales, the following criteria should be met [Konecny 1984]:

2. Resolution must be enough to show an object on the map (+/- 5m on 1:25,000 and +/-10m on

1:100,000); 3. The geometry must be reconstituted to +/- 10m for 1:25,000 and to +/- 20m for 1:100,000;

4. Imagery must allow for the determination of 25m contours.

3.2. MK-4 SPACE PHOTOGRAPHIC CAMERA

The MK-4 camera system consists of four lenses and four out of six bands or band combinations

may be selected for a certain earth coverage. The MK-4 camera is mounted on the Resurs-F2 spacecraft and is capable of taking pictures of the entire earth twice, or three times, during its 30-day

mission. The technical data of the MK-4 are as follows:

Principal Distance: 300 mm

Photograph Size: 180 mm x 180 mm Flying Height: 200 - 300 km

Photo Scale: 1:650,000 - 1:1,300,000

Area Coverage: 117 km x 117 km - 216 km x 216 km Ground Resolution: 6 - 8 m

Reference grid: Yes, 5 x 5 with 40 mm spacing

Bands: Z1 635 - 690 nm (B & W)

Z2 810 - 900 nm (IR B & W)

Z3 515 - 565 nm (B & W)

Z4 460 - 505 nm (B & W) Z5 580 - 800 nm (Spectrozonal False Colour)

Z6 400 - 700 nm (Colour)

The MK-4 film format of 180 mm x 180 mm allows photos to be easily evaluated on conventional

photogrammetric equipment such as an analytical stereo restitutor. The 60% forward overlap allows

stereo observation, 3D model restitution and stereo digitizing for the compilation of maps with positional accuracies of +/- 10m and elevation accuracies of +/- 15m, depending on the accuracy of the

ground control. Cost per sq km of image is USD 0.04 comparing to USD 0.14 for LANDSAT TM and

USD 0.74 for SPOT-Pan.

3.3. CONTROL AND RESTITUTION OF THE 3D MODEL

A pair of a MK-4 band Z1 photos in the range 635 - 690 nm of the Johannesburg area were used in the practical portion of this investigation. These photographs were used to form a three dimensional

model on the Adam Topocart analytical stereo restitutor. Coordinates of the projection center were as

follows:

Photo Number Latitude Longitude

0305 26 31' 27 22'

0306 25 50' 27 27'

Date of photography : August 18, 1989

Altitude of photography : 268.1km

Principal distance PD : 300.024mm





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Film type : T-27 (B & W) 635-690nm Resolving power : 195 l/mm

Ground coverage : 160km x 160km

Scale : 1:890,000

With satellite photography, control cannot be premarked on the ground. Reliance has therefore to

be placed on features which are identifiable on the satellite photographs. These features include: road intersections, corners of fields and houses, tree lines, rivers, canals, etc. The location, co-ordination

and heighting of these control points poses a problem. Three techniques of solving this problem were

attempted:

1. Contact printing and enlargement; 2. Slides 1:1 projected to 100:1 image;

3. Orthophoto maps 1:10,000.

This proved to be a fairly successful method for control point identification, especially the slides

which, once projected, allow for reasonably easy feature identification. For this experiment, in

addition to the Johannesburg photos, satellite photographs of the Munich area in Germany were used.

The Munich photographs were taken using a KFA-1000 camera with SN10 Spectrozonal film of the bands 560-680nm and 680-810nm. Locating and coordinating control points from 1:10,000 orthophoto

maps involves the identification of features (e.g. road intersections in the model), then locating the

orthophoto map on which that feature occurs. The coordinates would then be scaled off the orthophoto in the Gauss Conform coordinate system and the heights interpolated from 5 meter contour lines. The

most identifiable features in the stereo model were roads and road intersections, water features and

tree lines.

As the ground coverage is so large (160km x 160km), it spans two or three lines of longitude. The

South African co-ordinate system is based on the Gauss Conform Projection. The system consists of a

number of two degree wide zones, each with its own local co-ordinate system. Of the control points adopted, the majority are on the zone centred on the 27° line of longitude (Lo27), while a few are on

Lo29. A zone-to-zone transformation is required in order that all points are in the same co-ordinate

system. It was decided to use Lo27 as this zone contains the majority of points.

3.4. CORRECTIONS APPLIED TO STEREO MODEL

The photographs were taken from a high altitude of 268km. It was therefore essential that

corrections for earth curvature and atmospheric refraction be applied. These corrections were

incorporated with the lens distortion correction (radial and asymmetric in the form of an odd-powered

polynomial) and then applied. An absolute exterior orientation was to be computed using combinations of 12 of the control points entered. For a model of this scale and with the accuracy of

control being used, standard deviation of 10m in the X and Y ground co-ordinates and 20m in the Z

co-ordinate could be achieved.

After the absolute exterior orientation had been completed, the next step was to produce a thematic

map of a portion in the stereomodel. The digitized area contained such features as rivers and dams,

roads, urban areas and cultivated land. The area was digitized at a scale of 1:36,000 (chosen as it facilitated easy viewing on the screen) in line and continuous mode. A sample of the map is attached.





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3.5. CONCLUSIONS

Based on the findings of these investigations, the following conclusions may be drawn:

1. The stereo restitution of satellite photographs can be accomplished with acceptable accuracy and the quality of the stereo model produced is sufficient to enable digitizing;

2. The stereo digitization of satellite photograph models enables the production of medium

or small thematic and topographic maps;

3. The method of scaling co-ordinates off 1:10,000 orthophoto maps provided sufficiently

accurate ground control for the restitution of the satellite photos;

4. The corrections for earth curvature, atmospheric refraction and lens distortion must be

sufficiently modelled by the software to avoid decreasing the accuracy of the absolute exterior orientation;

5. It is possible to compile or revise a thematic map from satellite photographs with

sufficient feature identification and accuracy.

BIBLIOGRAPHY

Dowman I.,(1988) The Restitution of Metric Photography taken from Space, Int. Arch. Phot. Rem. Sens.,Vol 2,

pp.491-499.

Jacobsen K., Muller W., (1988) Geometric Potential of Space Images, Int. Arch. Phot. Rem. Sens., Vol 9,

pp.191-197.

Konecny G., (1984) The Evaluation of Spacelab 1 Photogrammetric Camera Data, Int. Arch.

Phot.Rem.Sens.,Vol1, pp.180-183.

Konecny G., Jacobsen K.,(1988) Comparison of High Resolution Satellite Imagery for Mapping. Int. Arch. Phot.

Rem. Sens. Vol9, pp.226-237.

Kraemer J., (1988) Map Production and Revision with Satellite Photographs taken by the MKF-6 camera and by

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