le, 
2. RÉSEAU CAMERAS 
The mathematical model of photogrammetric object 
reconstruction presumes the images to represent a 
perfect plane. When using a camera with rollfilm as 
the photographic medium, film flatness must be 
assured at the instant of exposure. This can be 
achieved mechanically by flattening against a vacuum 
plate or numerically by means of réseau techniques 
(Wester-Ebbinghaus, 1989). In addition, film 
deformation also may arise after exposure, e.g. as 
result of the development or adverse storage 
conditions. 
The geometric effect of film unflatness and any other 
deformation can be determined if the camera is 
equipped with a réseau plate as reference system, i.e. 
a glass plate with cross-shaped marks mounted in 
front of the film surface. The réseau is recorded onto 
the film by perspective projection together with the 
object. The cross positions can be measured and 
compared with their precisely calibrated counterparts 
on the grid plate. Displacements indicate the 
influence of film deformation to be eliminated by a 
meshwise numerical transformation of the image into 
the réseau plane. The smaller the mesh size, the 
higher will be the accuracy to determine local 
deformations. In general, the four adjacent réseau 
crosses are to be measured in addition to one object 
point. An automatic measurement is therefore 
advisable. 
Réseau cameras available on the market are listed in 
Table 1. 
The Linhof METRIKA 45 (Peipe, 1990) is a ruggedly 
built, compact camera for universal photogrammetric 
applications which, in spite of the relatively large 4x5" 
format remains rather handy and fully portable. A 
réseau plate is integrated into the camera body 
forming a rigid unit with the lens barrel. Precise click 
stops on the focusing mount determine reproducibly a 
(calibrated) set of interior orientation parameters. 
Film flattening is provided by combining the vacuum 
system installed in the rollfilm cassette with the réseau 
technique. Daylight loading cartridges accept 
approximately 5 m of 5" rollfilm, that corresponds to 
about 50 exposures. 
Table 1 Réseau Cameras 
To incorporate the METRIKA into the RolleiMetric 
industrial measurement system, a number of 
modifications were realized in cooperation between 
Rollei Fototechnic and Linhof. The principle idea was 
to enable the use of retroreflective targets in 
combination with high precision automatic image 
coordinate measurement employing the  Rollei 
Réseau-Scanner RS1. The joint efforts resulted in the 
R METRIKA, a camera which is especially adapted 
to industrial applications. 
3. R METRIKA 
The camera (Figs. 1 and 2, Tab. 2) is fixed to a 
rotation ring and can be continuously turned about its 
axis by + 180°. The integrated ring flash assures the 
ideal illumination of retroreflective targets (Fig. 3). 
The photographs then contain the images of the 
retrotargets clearly visible and detectable as dots of 
high contrast and sharpness. The photographic image 
itself with all the other object information is 
deliberately underexposed to create an optimum 
background for digital automatic point determination. 
For this reason, the amount of light coming from the 
object through the lens does not suffice to record the 
fine réseau crosses with high and uniform quality. 
Therefore, an active réseau illumination is achieved in 
the R_METRIKA by means of light-emitting diodes 
(LED’s) built into the lens (Figs. 2 and 4). This pre- 
illumination method, also used in the Rollei Large- 
Format Camera LFC and the Réseau-Scanning 
Camera RSC (Wester-Ebbinghaus, 1990; Dold und 
Riechmann, 1991) has proved very effective. 
Two lens systems, 75 mm wide angle and 150 mm 
normal lens are available (Tab. 2). They are equipped 
with an electronically driven, microprocessor- 
controlled shutter. To the back of the lens cone, a 
close-meshed réseau plate (2 mm grid spacing) is fixed 
(Fig. 2). In addition to the vacuum system which yields 
mechanical film flattening, the réseau serves for 
numerical correction of film deformation as 
mentioned above. On the other hand, the calibrated 
grid crosses of the camera form the reference system 
for the sensor orientation within the automatic image 
coordinate measurement process of the Réseau- 
Scanner RS1. 
  
  
  
Manufacturer Type Format Lens 
[mm2] [mm] 
Leica R5 24 x 36 15 - 180 
Rollei 3003 24 x 36 15 - 135 
Rollei 35 24 x 36 40 
Pentax PAMS 645P 45 x 60 45 
Hasselblad IDAC 60 x 60 38,70 
Rollei 6006 and 6008 60 x 60 40 - 350 
Linhof METRIKA 45 95 x 120 75, 90, 150 
GSI Inc. CRC -2 * 115x115 65, 90, 120 
GSI Inc. CRC -1 * 230 x 230 120, 240 
Rollei LFC 230 x 230 165, 210 
  
  
* with rear-projected réseau marks 
21