; A special mention should be 
made of some agencies for their prominent participation which 
permitted to draw efficient and numerous comparisons of pro- 
ducts; among them I would like to quote, (See LIST OF OPERATIVE CENTERS.) : 
. GID (DR), IGM (1), IGN (F), IPUS (D), ITPT (I).for prepa- 
ration of control, check points and contours. 
. IFAG (D), IGN (F), ITC (NL), for production of the major 
part of the required ortho and stereo-orthophotos, as well 
as NBS (SF), NLS (S) and the Wild Company (WH) for the 
useful complementary products they delivered. 
: . IGN (F), IPTU (A) for carrying out the major part of the 
measurements; NRC(CDN) and UCL (GB), for the additional 
part they were able to take regarding measurements. 
. IGN (F) and its school (E.N.S.G) that fostered completion 
of the test, so that full results could be obtained from 
these measurements and conclusions fully drawn. 
Five centers produced ortho and stereo-orthophotographs using a 
to WILD-OR 1 (IGN (F), ITC (NL), NB S (SF), NLS (S) and WH (CH) and 
a sixth center used a Zeiss- Z 2 (IFAG (D). 
MEASUREMENTS Six instruments were used for measurements onto the products deli- 
S vered to the four assessing centers, as follows 
i) IGN (F) used the ORTOSTER, a home made prototype, fitted 
with encoders,storing data on tapes. This ORTOSTER accepts 
a large format of size 330 x 570 mm, and has resolutions of 
2 cmm in x, y and 1 cmm in px, free hand motion, and fine- 
adjustement track-ball devices. 
ii) IPTU (A) used a STEREOGRAPH, from R and A.ROST C" (Wien,(A)) 
fitted with Diadur glass scale of 1 cmm resolution,storing 
data on tapes. The STEREOGRAPH accepts a very large format of 
size up to 550 x 750 mm, has a free hand motion and fine 
adjustment screws. 
iii) NRC (CDN) used its STEREOCOMPILER, built in its laboratories, 
which was specifically designed to accomodate stereo-orthopho- 
tos and had been in use for about twelve years for research 
purposes. 
This instrument accepts a very large format of size up to 
400 x 720 mm, has resolutions of 1 cmm but did not store data 
on tape,while delivering x, y and px listings; it has a free 
hand motion device with air bearings and a px micrometer. 
iiii) UCL (GB) used three types of instruments 
. a CP1 stereoplotter modified to plot from stereo-orthophotos, 
which accepts small formats of size 250 x 250 mm; it has 
n^ a free hand motion device and a px measurement by footwheel. 
. a KERN DSR1 analytical stereoplotter accepting a small format 
of 250 x 250 mm and storing very accurate data on a floppy 
disc. 
. a ROSS stereo-orthophoto plotter developped by ROSS Instruments 
Ltd., and commissioned by the OS (GB). The prototype was made 
available to UCL (GB). It accepts a large format of size 400 x 
400 mm and has a free hand motion devicé, a tracker ball and 
a joystick for px removal, ( ALI, J and I.J. DOWMAN ). 
Eight combinations of stereo-orthophoto printers and compilers 
were thus obtained. 
Each product or arrangement of products has been measured by 
two rounds, sometimes three rounds, each of them including 
E closure measurements on GCPs. 
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