Among those conditions are 
standard photogrammetric aerial survey 
similar classes of relief (from 100 m to 240 m as maximum 
elevation differences and 40 m to 75 m for the elevation 
standard deviation). 
similar scale-ranges as those used in the test 
regular distributions of GCPs and check points over the entire 
area of the orthophoto which covers the full original frame 
good proportions of well-defined features, with accurately 
fixed co-ordinates, used as GCPs and check points as well. 
Using signalised points is highly recommended (their propor- 
tion in the test was 33 %). 
an assessing method based on a similarity using a least-squares 
adjustment on at least seven points, and preferably twelve or 
fifteen points. 
a stereo-compiler allowing a pointing standard deviation of 
60 microns, resultant vector and two-round measurements. 
A slit width 
of 4 mm or 5 mm is recommended ,but a 8 mm slit can also provides 
similar results. 
Those general formulae are expressed as follows 
  
  
2 PHOTO \2 DTM Y ORTHO | 2 
exy 0.75 x( +2210) + 0.20 x( + 0.25 (IH) 
  
  
15 000 5 000 
x E 0 x( oa 2 + 0.10 DTM + 0.25 (ORTHO 2 
Zx : 15 000 ea HR TS 06 (5500 
2 PHOTO) 2 DTM Y oRTHOY ? 
e = 
Zy 0.30 (75000) + 0.50 x EN + 0.25 (5500) 
in which 
ex 7 r.m.s.e in planimetry (resultant vector) in meters, on 
y the ground, on natural points (including some targetted 
points), of the resulting orthophoto, off-line scanned 
in whatever x or y direction 
e2. ' Cz, = r.n.s.e in height, in meters, on the ground, on 
X y natural points (including some targetted points) of 
stereo-orthophoto-pairs off-line scanned resp. in the 
x and y directions. 
PHOTO = 1 : scale of the aerial survey (ranging from 16 K to 
60 K) to be rectified. 
DTM = 1 : scale of the DTM, i-e of the survey which was plot- 
ted into contours and gave rise to the DTM, (ranging 
from 16 K to.60 K). 
ORTHO = 1 : scale of the orthophoto and stereo-orthophoto 
(ranging from.5.K to 25 Kk), 
The scale ranges within which these formulae are applicable, can 
be somewhat extended towards both larger and smaller scales, 
as shown by some examples merging data from space and 
aerial surveys (see tabledi,exn' 11., 12 and 13), to obtain 
orthophotos at medium to large scale (1 : 10 K to 1 : 25 K), 
using aerial photographs at 1 : 30 K and 1 : 60 K-scale 
and D.T.M derived from SPOT data and/or, in the future, 
from new space projects at 5 m. pixel size, currently 
being developed by NASA, ESA or CNES, (see table 1 ). 
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