The test results are summarized in table 3.
MONO
STEREO
analyzed
ground
Pixel
traffic
buildings
ground vege-
waters
topogr.
terrain
interpreta-
examples
pixel
size
networks
tation
forms
model
tion
size
roads
paths
large
small
de-
forest
other
creek
ditch
gene-
buil-
tails
ral
dings
rural
orig.
+
+
4
+
4
4
+
+
0
♦
44
44
4-4
area
1.8 m
50 pm
4
4-
4
4
4
4
4-
4-
0
4
44
44
44
Vilie-
3.5 m
100 pm
4
4
4-
0
-
4
4
4
-
0
44
4
4
franche
7 m
200 pm
4
0
0
-
-
4
4
4
-
-
4
4
-
1:34000
14 m
400 pm
28 m
800 pm
city of
orig.
4
4
4
4
4
+
♦
4
+
4-4
+4-
++
Hannover
2.5 m
50 pm
♦
4
4
4
4
4-
4
4
4
4
+ t
44
1:50 000
5.0 m
100 pm
+
4-
4
0
0
4
4
0
4
4
4-4
+ 4-
10.0 m
200 pm
4-
0
0
-
-
4
0
-
0
4
4
0
15.0 m
300 pm
4
-
-
-
-
4
0
-
-
4
0
-
20.0 m
400 pm
-
-
-
-
-
-
-
-
-
-
-
40.0 m
800 pm
-
-
-
-
-
-
-
-
-
-
-
-
Island
orig.
4-
4
4-
-
4
4
0
0
4-4
+ 4
44
of Sylt
6.3 m
50 pm
4-
-
0
-
4
4
0
0
4-
44
44
1:125000
12.5 m
100 pm
4-
0
0
-
0
4
0
0
4
4-
4
25.0 m
200 pm
0
0
-
-
0
4
-
-
0
0
-
50.0 m
400 pm
-
-
-
-
-
-
-
-
-
-
-
100.0 m
L
800 pm
-
■
-
“
•
-
-
-
-
-
-
Table 3: Interpretation results
The following topographic features have been extracted: roads and paths,
buildings, vegetation (forest, trees and shrubs), creeks and ditches
and topographic forms.
The ability to interpret these features in the different images has been
indicated by the following symbols:
++ excellent; + good; o satisfactory; - not satisfactory;
blank not contained in image
The interpretation of the original images is satisfactory for all cases.
This is, of course, to be expected since small aerial photographs are
generally used for mapping. There is one slight exception in that buil
ding details such as ledges etc. cannot be detected in scales 1:125 000.
This is, however, not significant for the required map content 1:50 000.
In order to depict such building details pixel sizes between 2 and 5 m
are at least required.
The most significant result of the test is that stereo-observation is by
far superior to monoscopic observation. The stereoscopic advantage in
creases nearly proportional to the base height ratio.
The comparison between the different areas photographed shows clearly that
the interpretability of houses, roads, land forms, creeks and ditches
also varies with the type of the terrain since urban areas, rural areas
and uncultivated areas have generally different types of housing, roads
etc. even though they are of the same topographic feature category.
The most critical features are the buildings. To map them monoscopically
a pixel size of at least 3 m is required. Under stereoobservation a pixel
size of 6 m will suffice. This is the requirement for urban areas to map
at 1:50 000.
To map roads and vegetation this requirement may be slightly relaxed.
The results of investigating digitized images at 25 pm intervals were
identical to those in the original. Therefore they are not contained in
the table. This just proves that the observer's eye cannot resolve better
than about 5 to 10 lp/mm.
Interpretation under stereoobservation is possible for 50 pm and 100 pm
pixels. One may see stereo also for 200 pm and 400 pm pixels but this
does not aid in interpretation any more and does not permit contouring.
383