865
angular
range of
view
scale
in y
factors
-60°
1000
tO
to
+60°
100000
-60°
100
to
to
+60
10000
O
o
CT>
1
100
to
to
+90°
100000
- 5°
>1000000
to
satellites
+ 5°
-60°
to
+60°
0
"to
+ 5°
% 50000
and
>1000000
satellites
-60°
10000
to
to
+60
1000000
semi
annulus
constant
angle
10000
to
1000000
o
LO
100000
to
to
60°
1000000
o
LO
100000
to
1000000
70°
45° 1000
to to
70° 10000
2. Production of Geometrically Correct Thematic Maps for, e.g., agriculture,
land use, oceanography and geography will be important to somewhat lower
accuracy requirements than for topographic mapping. But a geometric
restitution is required especially for scanners with panoramic distortion
since depicted detail could not otherwise be correlated visually to
reality. Despite the relatively low ground resolution of 1 to 20 m
attainable from low flying heights, multispectral scanners due to their
high spectral resolution offer the best possibility for object
classification. Geometrical restitution of satellite multispectral
scanner images is less of a problem, since images are already reproduced
in bulk-rectified form and since topographic displacements are negligible.
The geometric contribution for thematic mapping will best have to be
made at the preprocessing stage. Studies are required to test present
procedures used for producing ERTS imagery and other types of images
obtained by multispectral scanning.
3. Production of a Geometric Base for Semiautomatic or Automatic Comparison
of spatially, spectrally and temporally different images to and beyond
resolution limits is a requirement for all types of imagery, especially
for images from multispectral and IR scanners. Only then change
detection may be studied with image analyzers or computer analysis.
These problems are currently underestimated by the user.
It is the aim of the working group to deal with problems of
geometrical restitution for the 3 mentioned purposes. This work must be
carried out in various steps:
a) Analytical Analysis
It consists of the formulation of a mathematical model, the
measurement of image coordinates with a suitable instrument (compara
tor) and a test in which computed ground coordinates derived from the
measurements via the mathematical model are compared with known
ground coordinates in a test area.
Tests of this nature have been conducted by members of the working
group. They are being published (in English) in the journal of the
German Society of Photogrammetry "Bildmessung und Luftbildwesen"
Vol. 1975/1. These tests have established that differential
rectification of the images according to correction functions
derived from ground control may result in geometric position
accuracies of 3 times the resolution for radar, of 2 times the
resolution for thermal and multispectral scanners used from aircraft
and of slightly better than resolution for satellite scanner images.
Standard aerial photography permits the evaluation of the geometry
to better than 1/3 of the resolution.
In obtaining this accuracy an interpolation procedure is used between
control points (polynomials, least squares).
