- Email: [email protected]
Instruments recently developed for architectural photogrammetry
Photogrammetria
INSTRUMENTS RECENTLY DEVELOPED FOR ARCHITECTURAL PHOTOGRAMMETRY MAURICE CARBONNELL
Photogrammetry Service, National Geographical Institute, Paris (France) (Received December 2, 1974) ABSTRACT Carbonnell, M., 1975. Instruments recently developed for architectural photogrammetry. Photogrammetria, 30:107-113. This paper first analyses the special problems posed by architectural and archeological photogrammetric surveys, i.e., problems of accuracy and their consequences on the choice of base-line and camera, together with difficulties due to: (a) the surroundings of the subject; (b) the extension of the m o n u m e n t or archeological site; and (c) the wide-range of camera distances. There is no universal solution to these problems, but recent developments of terrestrial photogrammetric equipment to a large extent meet these constraints: (a) by a widening of the range of available focal lengths; (b) by the possibility to modify the principal distances of cameras in order to be able to photograph clearly at different distances; (c) by the introduction of devices enabling one to use large standard slope angles of the principal axes; (d) by a suitable adaptation of plotting instruments to the wide-range of principal distances involved and giving them a fairly satisfactory z range. The problems concerning emulsion bases are also discussed. INTRODUCTION
In order to understand recent developments of the instruments used for architectural and archeological photogrammetric surveys one must first consider the special problems arising from such surveys.
Problems of accuracy There are two conditions which must always be remembered: (a) The base-line camera/distance ratio should be within reasonable limits and not be too small (1/15 seems to be a minimum, occasionally 1/20); this entails the use of stereometric cameras for photography at short distances, because it is difficult to have short base-lines with two independent tripods, together with individual cameras for long-distance photography; the two types of camera are absolutely necessary. (b) The scale of the photograph, i.e., the principal distance/camera distance ratio, must not be too small with respect to the survey scale (a ratio of 1/7 or 1/8 seems to be limit); if the camera distance, for various reasons, has to be rather large, one must increase the principal distance; short focal length cameras, which are now widely used, may therefore not be sufficient, and in order to cover the entire range of work that arises it is necessary to have longer focal-length cameras as well.
108
Photographic operations For both interior and exterior photography, the surroundings of the subject to be surveyed often impose constraints and in particular the need to be far away, which is often not optimal. This problem may make it necessary: (a) to introduce a certain convergence of the axes; hence the necessity for separate cameras; (b) to use a wide field of view which corresponds with the tendencies of recent instruments; (c) to climb up and take photographs from neighbouring buildings, use ladders, lifts or sometimes even a helicopter; (d) to incline the principal axis strongly; the constraints are then imposed by the plotting equipment and require the use of standard inclinations and the adaptation of the camera supports for them. Horizontal extent of monuments and archeological sites The consequences of these extensions concern, on the one hand, the plotting instruments which are all the better adapted to architectural photogrammetry if they have a large z range, and, on the other hand, the metric cameras, which must provide sharp images; in order to have a sufficient depth of field, it is very necessary that the objective lenses should be sufficiently stopped down. Wide-range of camera distances The complete range of architectural and archeological photogrammetry applications requires camera distances going from infinity (in the photographic sense of the term) to several tenths of a metre. It is thus necessary, either to have a series of cameras to cover the range of camera distances, or be able to vary the principal distance; the latter solution, abandoned by photogrammetrists because of the high mechanical and optical standards required (particularly the distortion, which if not zero, varies considerably with the camera focussing), is now being reexamined by the manufacturers. Consequently, there is a wide range of working conditions to be considered, and as there is no universal solution one must accept that a range of equipment is necessary. It is towards this range of equipment and also a wider range of uses that the photogrammetric instruments suitable for architectural and archeological surveys have evolved in recent years. We discuss below, in turn, the different technical criteria to be satisfied and the different solutions adopted for each of them. VARIOUS PRINCIPAL DISTANCES
The phototheodolites, basically produced for topographical surveys by terrestrial photogrammetry, were once and are still sometimes used for architectural surveys. They are not particularly useful because they have narrow fields of view.
109 They have long focal lengths and some are still made such as: Zeiss Jena Phototheo : f = 190 mm, 13 X 18 cm format Officine Galileo F T G . l b : f = 155 mm, 10 X 15 cm format. More recently cameras have been produced with short principal distances and wide fields of view. In this category are the largest number of instruments now being produced, e.g., (a) all the stereometric cameras (except the Officine Galileo Veroplast with f = 150 mm, and 13 X 18 cm format) Carl Zeiss SMK-40 Carl Zeiss SMK-120
(B = 40 cm) (B = 120 cm)
f = 60 mm, 9 X 12 cm format
Wild C-40 Wild C-120
(B = 40 cm) (B = 120 cm)
f = 64 mm, 6.5 X 9 cm format
Zeiss Jena SMK-5.5/0808 Zeiss Jena SMK-5.5/0808
(B = 40 cm) (B = 120 cm)
f = 56 mm, 8 X 8 cm format
Nikon TS-20
(B = 20 cm)
f = 64 mm, 6.5 X 9 cm format
Nikon TS-40 Nikon TS-120
(B = 40 cm) (B = 120 cm)
f=
60ram
t9 X 12 cm format 6.5 X 9 c r n format.
(b) small format individual cameras: CarlZeissTMK-6 : f = 6 0 m m , 9 X 1 2 c m format WildP-32 : f = 6 4 m m , 6.5 X 9 c m format Hasselblad MK-70 Biogon : f =- 60 mm, 6 X 6 cm format the last two of these being the most recent. It should be noted that in the Wild camera the reduction of the field of view, due to the smaller format, is partly compensated by an off-centering of the principal point on the negative. More recently the necessity to have cameras with much longer focal lengths has encouraged manufacturers to build new devices having focal lengths intermediate between those of the small cameras and those of the phototheodolites, the most useful ones still retaining a large field of view. During recent years one has been able to purchase: Officine Galileo Verostat : f = 100 mm, 9 X 12 cm format Carl Zeiss TMK-12 : f =- 120 mm, 9 N 12 cm format Zeiss Jena U M K : f = 100 mm, 13 N 18 cm format Hasselblad MK-70 Planar : f = 100 mm, 6 X 6 cm format Wild P-31 : f = 100 mm, 4 X 5" format (principal point off centre). The group of 21 cameras discussed in this section cover all the terrestrial photogrammetric cameras currently available, to which one should add the various Japanese Sokkisha cameras which do not yet seem to be available for export.
110 VARIABLE PRINCIPAL DISTANCES
It is possible to slightly modify the principal distance of a camera in order to focus at different camera distances. This facility which, as already mentioned, is being re-examined by the manufacturers following upon recent optical and mechanical advances, is available with different cameras and is based on the following four different technical solutions: (a) displacement of the objective lens by a spiral movement: Officine Galileo cameras Hasselblad MK-70 cameras; (b) displacement of the objective lens by a translatory movement: Zeiss Jena UMK; (c) introduction of rings of different thicknesses between the camera chassis and the lens: Wild P-31; (d) additional lenses in front of the objective: Carl Zeiss TMK-6 and SMK (5 sets of lenses). LARGE INCLINATIONS
Some rather old plotting instruments are able to process photographs of steep slopes. However, these instruments are hardly compatible with modern terrestrial cameras, particularly small format cameras, and some of them are no longer, or soon will be no longer manufactured. An idea of Dr. H. Foramitti, first adopted by Carl Zeiss and later by all the other manufacturers consists, as already mentioned, in giving the camera a large well-determined slope angle, and also adding a simple device to the plotting instruments in order to process the photographs taken under these conditions, so long as the photographs are taken in the "normal case". On the cameras, the required inclination is obtained either by use of an offset level or the use of a circular quadrant with indentations. These devices are to be found on: Carl Zeiss T M K and SMK Wild C and P 31 (the P.32, fixed on a theodolite can be given any inclination which can be accurately determined) Zeiss Jena SMK and U M K Officine Galileo Verostat (these cameras have a continuous inclination range) Nikon TS. The additional device for the plotting instruments is an "inclination calculator" and it is introduced into the system between the plotter itself and the plotting table; it makes the necessary correction to the y plotting movements. This calculator can now be made available for the following instruments:
111 Carl Zeiss Terragraph and Planimat D-2 Wild A-40 Zeiss Jena Technocart and Stereometrograph F Nikon TR-2. The large camera inclinations, e.g., 30 ° and 60 ° or 30 ° and 70 °, are incompatible with those accepted by photogrammetric rectifiers, basically conceived for aerial photographs, and this incompatibility increases with decreasing camera focal length. In order to be able to rectify photographs obtained under such conditions, special devices must be constructed fo.r particular conditions (a particular slope angle, a particular focal length). Only Carl Zeiss actually markets such a device (KEG-30). A D A P T A T I O N OF P L O T T I N G I N S T R U M E N T S TO A W I D E RANGE O F P R I N C I P A L DISTANCES
This range and the resulting need to adapt the plotting instruments are not problems particular to terrestrial photogrammetry. In aerial photogrammetry as well, the modern plotting instruments now have greatly reduced capabilities for processing inclined photographs as compared with certain older equipment such as the Stereoplanigraph, Autographe A-7 or the Photostereograph Beta 2; on the other hand, they generally have greater versatility as regards focal lengths and are able to process photographs taken with all the aerial cameras currently in use, which have principal distances ranging from 85 to 310 mm. However, in architectural photogrammetry, the considerable use of smallformat metric cameras necessitates a further extension of plotting capabilities towards short focal lengths in the 50- or 60-ram range. The following three solutions have been devised: (a) the construction of special equipment solely for this type of photograph supposed to have been taken in the "normal case"; this solution which is not very recent, gave rise to the Carl Zeiss Terragraph, the Wild A-40 Autographe and, more recently, the Nikon TR-2; (b) the selection of a fairly wide range of focal lengths, but tending towards the shorter ones as compared with aerial pho~ogrammetry equipment, e.g., Zeiss Jena Technocart (f from 50 to 215 mm); (c) as the most recent solution, the manufacture of additional devices for the plotting of small-camera photographs, e.g., Carl Zeiss devices for the Planimat D-2. D E P T H O F F I E L D O F A SUBJECT: Z RANGE O F P L O T T I N G I N S T R U M E N T S
Two aspects of this problem have already been mentioned: (a) camera depth of field augmented by increased stopping: down (f : 22): thus the Wild C.120 enables one to work between 2.70 m and infinity; in this solution short focal lengths are favoured;
112 (b) sufficient z range in the plotting instruments. With respect to this second point the simplified instruments constructed for the short principal distances and the normal case have very useful properties (except for the Technocart which is more limited): Carl Zeiss Terragraph Wild A-40 Nikon TR-2
: 60 m m - 6 1 0 mm : 40 mm-(500-f) mm : 80 m m - 5 0 0 mm.
Unfortunately, the capabilities of the new, more or less universal, instruments, are smaller than those of the older models where the z range went, for example, from 170 to 605 mm (Stereoplanigraph C-8) or 140-700 mm (Photostereograph Beta 2). They are generally limited to a range of the order of 300 ram, the best being that of the Stereocartograph V of Officine Galileo (375 mm); this range is usually sufficient but may not be so in all cases and in any case it usually imposes restrictions on the scale of the model formed in the instrument. EMULSION BASES
Two view points need to be considered: (a) for highly accurate work it is necessary to use thick glass supports instead of the usual plates and the chassis of recent metric cameras with large formats can accommodate them; (b) the use of film hardly ever arises in architectural photogrammetry where plates can always be used, except in the special case where colour photographs are required for which emulsions on plates do not exist; however, such photographs can be very useful if the subject is very coloured; and even in certain special cases due to the stone colourations and the lighting conditions, colour photography can improve the interpretation during plotting. In addition to the Hasselblad MK-70 camera which can only take films and the Wild P-32 camera which in addition to plates can use film-packs and rolled film (but under poor flatness conditions) the best solution of this problem is that of the UMK camera for which Zeiss Jena has recently issued a film magazine achieving flatness by suction. This survey of the recent developments in photogrammetric equipment suitable for architectural and archeological surveys has shown the enormous efforts being made by the manufacturers to adapt their products and the imaginative feats of those that use them. It also appears, as mentioned above, that there is no one particular instrument which can be used for all types of surveys. A fairly wide range of equipment is always needed (Fig.l). If, however, one must find the best solution with only a metric camera and a plotting machine available it would best to have: (a) a fairly long focal length camera (about 100 mm) with a fairly wide field of view equipped with a device for varying the principal distance;
113
Fig.l. Terrestrial metric cameras used by the Architectural and Archeological Photogrammetry Centre of the Institut Geographique National, France. I = TMK-6 Carl Zeiss; 2 C-40 Wild; 3 =- Hasselblad transformed into a metric camera and mounted on a special device for surveying small archeological objects; 4 - P-31 Wild; 5 -- U M K 10/1318 Zeiss Jena; 6 - SMK-120 Carl Zeiss: 7 CA 1.G.N. Camera with 125 mm focal length and 18 X 18 cm format, constructed in the I.G.N. laboratories; 8 P-32 Wild. N.B. It is worthwhile also mentioning a long focal length camera (f: 300 mm, 18 X 18 cm format) constructed in the I.G.N. laboratories. (b)
a p l o t t i n g i n s t r u m e n t as u n i v e r s a l as p o s s i b l e s o f a r as c o n c e r n s b o t h
s l o p e s ( e v e n if o n e h a s t o u s e a n i n c l i n a t i o n c a l c u l a t o r ) a n d z r a n g e . T h e u s e a n d d e v e l o p m e n t o f a n a l y t i c e q u i p m e n t s h o u l d l e a d to r e a l p r o g r e s s in this d o m a i n .
INSTRUMENTS RECENTLY DEVELOPED FOR ARCHITECTURAL PHOTOGRAMMETRY MAURICE CARBONNELL
Photogrammetry Service, National Geographical Institute, Paris (France) (Received December 2, 1974) ABSTRACT Carbonnell, M., 1975. Instruments recently developed for architectural photogrammetry. Photogrammetria, 30:107-113. This paper first analyses the special problems posed by architectural and archeological photogrammetric surveys, i.e., problems of accuracy and their consequences on the choice of base-line and camera, together with difficulties due to: (a) the surroundings of the subject; (b) the extension of the m o n u m e n t or archeological site; and (c) the wide-range of camera distances. There is no universal solution to these problems, but recent developments of terrestrial photogrammetric equipment to a large extent meet these constraints: (a) by a widening of the range of available focal lengths; (b) by the possibility to modify the principal distances of cameras in order to be able to photograph clearly at different distances; (c) by the introduction of devices enabling one to use large standard slope angles of the principal axes; (d) by a suitable adaptation of plotting instruments to the wide-range of principal distances involved and giving them a fairly satisfactory z range. The problems concerning emulsion bases are also discussed. INTRODUCTION
In order to understand recent developments of the instruments used for architectural and archeological photogrammetric surveys one must first consider the special problems arising from such surveys.
Problems of accuracy There are two conditions which must always be remembered: (a) The base-line camera/distance ratio should be within reasonable limits and not be too small (1/15 seems to be a minimum, occasionally 1/20); this entails the use of stereometric cameras for photography at short distances, because it is difficult to have short base-lines with two independent tripods, together with individual cameras for long-distance photography; the two types of camera are absolutely necessary. (b) The scale of the photograph, i.e., the principal distance/camera distance ratio, must not be too small with respect to the survey scale (a ratio of 1/7 or 1/8 seems to be limit); if the camera distance, for various reasons, has to be rather large, one must increase the principal distance; short focal length cameras, which are now widely used, may therefore not be sufficient, and in order to cover the entire range of work that arises it is necessary to have longer focal-length cameras as well.
108
Photographic operations For both interior and exterior photography, the surroundings of the subject to be surveyed often impose constraints and in particular the need to be far away, which is often not optimal. This problem may make it necessary: (a) to introduce a certain convergence of the axes; hence the necessity for separate cameras; (b) to use a wide field of view which corresponds with the tendencies of recent instruments; (c) to climb up and take photographs from neighbouring buildings, use ladders, lifts or sometimes even a helicopter; (d) to incline the principal axis strongly; the constraints are then imposed by the plotting equipment and require the use of standard inclinations and the adaptation of the camera supports for them. Horizontal extent of monuments and archeological sites The consequences of these extensions concern, on the one hand, the plotting instruments which are all the better adapted to architectural photogrammetry if they have a large z range, and, on the other hand, the metric cameras, which must provide sharp images; in order to have a sufficient depth of field, it is very necessary that the objective lenses should be sufficiently stopped down. Wide-range of camera distances The complete range of architectural and archeological photogrammetry applications requires camera distances going from infinity (in the photographic sense of the term) to several tenths of a metre. It is thus necessary, either to have a series of cameras to cover the range of camera distances, or be able to vary the principal distance; the latter solution, abandoned by photogrammetrists because of the high mechanical and optical standards required (particularly the distortion, which if not zero, varies considerably with the camera focussing), is now being reexamined by the manufacturers. Consequently, there is a wide range of working conditions to be considered, and as there is no universal solution one must accept that a range of equipment is necessary. It is towards this range of equipment and also a wider range of uses that the photogrammetric instruments suitable for architectural and archeological surveys have evolved in recent years. We discuss below, in turn, the different technical criteria to be satisfied and the different solutions adopted for each of them. VARIOUS PRINCIPAL DISTANCES
The phototheodolites, basically produced for topographical surveys by terrestrial photogrammetry, were once and are still sometimes used for architectural surveys. They are not particularly useful because they have narrow fields of view.
109 They have long focal lengths and some are still made such as: Zeiss Jena Phototheo : f = 190 mm, 13 X 18 cm format Officine Galileo F T G . l b : f = 155 mm, 10 X 15 cm format. More recently cameras have been produced with short principal distances and wide fields of view. In this category are the largest number of instruments now being produced, e.g., (a) all the stereometric cameras (except the Officine Galileo Veroplast with f = 150 mm, and 13 X 18 cm format) Carl Zeiss SMK-40 Carl Zeiss SMK-120
(B = 40 cm) (B = 120 cm)
f = 60 mm, 9 X 12 cm format
Wild C-40 Wild C-120
(B = 40 cm) (B = 120 cm)
f = 64 mm, 6.5 X 9 cm format
Zeiss Jena SMK-5.5/0808 Zeiss Jena SMK-5.5/0808
(B = 40 cm) (B = 120 cm)
f = 56 mm, 8 X 8 cm format
Nikon TS-20
(B = 20 cm)
f = 64 mm, 6.5 X 9 cm format
Nikon TS-40 Nikon TS-120
(B = 40 cm) (B = 120 cm)
f=
60ram
t9 X 12 cm format 6.5 X 9 c r n format.
(b) small format individual cameras: CarlZeissTMK-6 : f = 6 0 m m , 9 X 1 2 c m format WildP-32 : f = 6 4 m m , 6.5 X 9 c m format Hasselblad MK-70 Biogon : f =- 60 mm, 6 X 6 cm format the last two of these being the most recent. It should be noted that in the Wild camera the reduction of the field of view, due to the smaller format, is partly compensated by an off-centering of the principal point on the negative. More recently the necessity to have cameras with much longer focal lengths has encouraged manufacturers to build new devices having focal lengths intermediate between those of the small cameras and those of the phototheodolites, the most useful ones still retaining a large field of view. During recent years one has been able to purchase: Officine Galileo Verostat : f = 100 mm, 9 X 12 cm format Carl Zeiss TMK-12 : f =- 120 mm, 9 N 12 cm format Zeiss Jena U M K : f = 100 mm, 13 N 18 cm format Hasselblad MK-70 Planar : f = 100 mm, 6 X 6 cm format Wild P-31 : f = 100 mm, 4 X 5" format (principal point off centre). The group of 21 cameras discussed in this section cover all the terrestrial photogrammetric cameras currently available, to which one should add the various Japanese Sokkisha cameras which do not yet seem to be available for export.
110 VARIABLE PRINCIPAL DISTANCES
It is possible to slightly modify the principal distance of a camera in order to focus at different camera distances. This facility which, as already mentioned, is being re-examined by the manufacturers following upon recent optical and mechanical advances, is available with different cameras and is based on the following four different technical solutions: (a) displacement of the objective lens by a spiral movement: Officine Galileo cameras Hasselblad MK-70 cameras; (b) displacement of the objective lens by a translatory movement: Zeiss Jena UMK; (c) introduction of rings of different thicknesses between the camera chassis and the lens: Wild P-31; (d) additional lenses in front of the objective: Carl Zeiss TMK-6 and SMK (5 sets of lenses). LARGE INCLINATIONS
Some rather old plotting instruments are able to process photographs of steep slopes. However, these instruments are hardly compatible with modern terrestrial cameras, particularly small format cameras, and some of them are no longer, or soon will be no longer manufactured. An idea of Dr. H. Foramitti, first adopted by Carl Zeiss and later by all the other manufacturers consists, as already mentioned, in giving the camera a large well-determined slope angle, and also adding a simple device to the plotting instruments in order to process the photographs taken under these conditions, so long as the photographs are taken in the "normal case". On the cameras, the required inclination is obtained either by use of an offset level or the use of a circular quadrant with indentations. These devices are to be found on: Carl Zeiss T M K and SMK Wild C and P 31 (the P.32, fixed on a theodolite can be given any inclination which can be accurately determined) Zeiss Jena SMK and U M K Officine Galileo Verostat (these cameras have a continuous inclination range) Nikon TS. The additional device for the plotting instruments is an "inclination calculator" and it is introduced into the system between the plotter itself and the plotting table; it makes the necessary correction to the y plotting movements. This calculator can now be made available for the following instruments:
111 Carl Zeiss Terragraph and Planimat D-2 Wild A-40 Zeiss Jena Technocart and Stereometrograph F Nikon TR-2. The large camera inclinations, e.g., 30 ° and 60 ° or 30 ° and 70 °, are incompatible with those accepted by photogrammetric rectifiers, basically conceived for aerial photographs, and this incompatibility increases with decreasing camera focal length. In order to be able to rectify photographs obtained under such conditions, special devices must be constructed fo.r particular conditions (a particular slope angle, a particular focal length). Only Carl Zeiss actually markets such a device (KEG-30). A D A P T A T I O N OF P L O T T I N G I N S T R U M E N T S TO A W I D E RANGE O F P R I N C I P A L DISTANCES
This range and the resulting need to adapt the plotting instruments are not problems particular to terrestrial photogrammetry. In aerial photogrammetry as well, the modern plotting instruments now have greatly reduced capabilities for processing inclined photographs as compared with certain older equipment such as the Stereoplanigraph, Autographe A-7 or the Photostereograph Beta 2; on the other hand, they generally have greater versatility as regards focal lengths and are able to process photographs taken with all the aerial cameras currently in use, which have principal distances ranging from 85 to 310 mm. However, in architectural photogrammetry, the considerable use of smallformat metric cameras necessitates a further extension of plotting capabilities towards short focal lengths in the 50- or 60-ram range. The following three solutions have been devised: (a) the construction of special equipment solely for this type of photograph supposed to have been taken in the "normal case"; this solution which is not very recent, gave rise to the Carl Zeiss Terragraph, the Wild A-40 Autographe and, more recently, the Nikon TR-2; (b) the selection of a fairly wide range of focal lengths, but tending towards the shorter ones as compared with aerial pho~ogrammetry equipment, e.g., Zeiss Jena Technocart (f from 50 to 215 mm); (c) as the most recent solution, the manufacture of additional devices for the plotting of small-camera photographs, e.g., Carl Zeiss devices for the Planimat D-2. D E P T H O F F I E L D O F A SUBJECT: Z RANGE O F P L O T T I N G I N S T R U M E N T S
Two aspects of this problem have already been mentioned: (a) camera depth of field augmented by increased stopping: down (f : 22): thus the Wild C.120 enables one to work between 2.70 m and infinity; in this solution short focal lengths are favoured;
112 (b) sufficient z range in the plotting instruments. With respect to this second point the simplified instruments constructed for the short principal distances and the normal case have very useful properties (except for the Technocart which is more limited): Carl Zeiss Terragraph Wild A-40 Nikon TR-2
: 60 m m - 6 1 0 mm : 40 mm-(500-f) mm : 80 m m - 5 0 0 mm.
Unfortunately, the capabilities of the new, more or less universal, instruments, are smaller than those of the older models where the z range went, for example, from 170 to 605 mm (Stereoplanigraph C-8) or 140-700 mm (Photostereograph Beta 2). They are generally limited to a range of the order of 300 ram, the best being that of the Stereocartograph V of Officine Galileo (375 mm); this range is usually sufficient but may not be so in all cases and in any case it usually imposes restrictions on the scale of the model formed in the instrument. EMULSION BASES
Two view points need to be considered: (a) for highly accurate work it is necessary to use thick glass supports instead of the usual plates and the chassis of recent metric cameras with large formats can accommodate them; (b) the use of film hardly ever arises in architectural photogrammetry where plates can always be used, except in the special case where colour photographs are required for which emulsions on plates do not exist; however, such photographs can be very useful if the subject is very coloured; and even in certain special cases due to the stone colourations and the lighting conditions, colour photography can improve the interpretation during plotting. In addition to the Hasselblad MK-70 camera which can only take films and the Wild P-32 camera which in addition to plates can use film-packs and rolled film (but under poor flatness conditions) the best solution of this problem is that of the UMK camera for which Zeiss Jena has recently issued a film magazine achieving flatness by suction. This survey of the recent developments in photogrammetric equipment suitable for architectural and archeological surveys has shown the enormous efforts being made by the manufacturers to adapt their products and the imaginative feats of those that use them. It also appears, as mentioned above, that there is no one particular instrument which can be used for all types of surveys. A fairly wide range of equipment is always needed (Fig.l). If, however, one must find the best solution with only a metric camera and a plotting machine available it would best to have: (a) a fairly long focal length camera (about 100 mm) with a fairly wide field of view equipped with a device for varying the principal distance;
113
Fig.l. Terrestrial metric cameras used by the Architectural and Archeological Photogrammetry Centre of the Institut Geographique National, France. I = TMK-6 Carl Zeiss; 2 C-40 Wild; 3 =- Hasselblad transformed into a metric camera and mounted on a special device for surveying small archeological objects; 4 - P-31 Wild; 5 -- U M K 10/1318 Zeiss Jena; 6 - SMK-120 Carl Zeiss: 7 CA 1.G.N. Camera with 125 mm focal length and 18 X 18 cm format, constructed in the I.G.N. laboratories; 8 P-32 Wild. N.B. It is worthwhile also mentioning a long focal length camera (f: 300 mm, 18 X 18 cm format) constructed in the I.G.N. laboratories. (b)
a p l o t t i n g i n s t r u m e n t as u n i v e r s a l as p o s s i b l e s o f a r as c o n c e r n s b o t h
s l o p e s ( e v e n if o n e h a s t o u s e a n i n c l i n a t i o n c a l c u l a t o r ) a n d z r a n g e . T h e u s e a n d d e v e l o p m e n t o f a n a l y t i c e q u i p m e n t s h o u l d l e a d to r e a l p r o g r e s s in this d o m a i n .