The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B4. Beijing 2008
The percentage of entities belonging to each group is reported,
as example, in table 2. According to this percentage, it was
possible to classify this level in:
• Metrically plotted, if at least 95% of the cases belong
to Group A (P);
• Visible, if only 60% of the case belong to Group A
and 35% to Group B (V);
• Not visible (NV).
A map scale was chosen if all the levels were in the P category.
This final subdivision is shown in the last column in table 2.
These procedure were repeated, for each available flight, and, in
each case a map scale was chosen.
2.1 ADS40 1 st Generation
The available images were taken by this sensor at an altitude of
6000 m, with a GSD of about 62 cm. In spite of this, the quality
of images is good, especially coloured ones. Two different
areas were acquired with the same GSD: one over the city of
Turin (Italy) and the other over the Susa Valley, the location of
the 2006 Winter Olympic Games.
Figure 2. An Example of the map entities stereoplotted from
the ADS40 1 st generation of the Susa Valley
According to our methodology, it was expected that a 1:10000
map scale (figure 2) would be extracted from these images.
Map entities
Group
A
Group
B
Group
C
Road and railway
96%
4%
0/9
P
Buildings, urban
furniture, technical
buildings
100%
0%
0%
P
Water, rivers,
channels, water
works, etc.
100%
0%
0%
P
Energy, material,
fluid pipelines
95%
5%
0%
P
Man-made Territorial
divisions
100%
0%
0%
P
Break lines
100%
0%
0%
P
Vegetation
100%
0%
0%
P
TOTAL %
98%
2%
0%
P
Table 2. Map entity levels and sub-levels
The analysis of the results is summarized in table 2. The
performed analysis has confirmed the expectations. The colour
images helped to detect different objects and to distinguish,
according to their colour, different entities, such as stone walls
from brick walls.
However some map details were not metrically plotted as
requested in technical specifications because of their reduced
dimensions in the images. For example the sky-lift pylons in
figure 3 are shown as they appeared at zoom 1:1: this kind of
entity is obviously difficult to detect and even more difficult to
plot.
The GSD 0.62 m can, to a certain extent, be considered the
maximum suitable dimension in 1:10000 map production. In
general, a maximum GSD of 0.60 m is suggested for this map
scale.
Figure 3. Sky-lift pylons in a ADS40 image (zoom 1:1)
2.2 ADS40 2 nd Generation
This sensor acquired images during two flight performed at
different altitude over the city of Romanshom (Switzerland).
One flight was performed at about a height of 1000 m and with
a GSD of 0.10 m. The second flight, which was flight at an
altitude of 2000 m, instead had a GSD of 0.20 m.
Both flights acquired good quality images. An example of the
images from the first flight images is shown in figure 4 while an
example of the 0.20 m GSD images is given in figure 5.
Figure 4. Urban area acquired by ADS40 2 nd generation,
GSD=0.10 m (zoom 1:1,4:1)