most of the measuring operations and carried out the subsequent analysis 
of the results. 
Outline of the Orthophoto Experiment 
The participating manufacturers were provided with the following 
material for producing the experimental data: 
Contact diapositives of a stereopair (scale 1:10 000, overlap 60%) 
taken witha Wild RC8 camera (230 mm x 230 mm, f = 153 mm) equipped 
with a 1 cm reseau plate 
Camera calibration data 
XYZ terrain coordinates of six targeted control points 
Paper prints of the photographs with ground control points marked. 
Each participant was asked to provide the Working Group with: 
Original orthophoto negatives from both photographs of the stereo- 
pair on dimensionally stable material; the orthophoto scale re- 
quested was 1:2 500 
Contour lines or drop lines: contour interval 2.5 m 
Record of t the profile data if the profiles were recorded. 
If the equipment did not allow a 4X enlargement of the original 
photographs, the participant was free to select a suitable enlargement 
factor. 
Table I lists the instruments used in the experiment, the scale 
of orthophotos, the type of height information that was provided by the 
participants, and information on the operational mode. 
The Test Area 
The area selected for the experiment is located near Ripon, 
+ 
OT 
Quebec, in the vicinity of Ottawa. It consists of rolling farmland with 
some wooded parts. Elevation differences within the area covered by the 
stereopair are approximately 80 metres with slopes of up to 30? and an 
average slope of 10°. The many open hills in the test area are particu- 
larly suited for evaluating the accuracy of planimetric and height 
information provided by the orthophoto technique. On the other hand, 
buildings and isolated groups of trees in the area offer a possibility