The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B4. Beijing 2008 
As in all the previous examples the image quality was very high 
as shown in figure 8. Each map detail was in fact easily 
recognizable and could be easily plotted. 
Figure 7. Urban area acquired by DMC (zoom 1:1,4:1) 
Map sale 
Group 
A 
Group 
B 
Group 
C 
1:500 
87% 
13% 
0% 
V 
1:1000 
100% 
0% 
0% 
p 
Table 5. Comparison between 1:500 and 1:1000 map scale 
Figure 8. Urban area acquired by 3-DAS-1 (zoom 1:1, 4:1) 
3. CONCLUSION 
In this paper digital images acquired from several digital 
sensors were analyzed from a semantic point of view in order to 
evaluate the differences with scanned analogue cameras and to 
propose new GSD values for different map scale production. 
According to the performed analysis, digital cameras seem to 
give better quality images than scanned analogue images. 
In order to realize a certain map scale, digital cameras allow 
flights with a larger GSD to be performed. In particular, the 
following equation is suggested: 
GSD CD = gGSD AI (1) 
where GSD dc =GSD in digital cameras 
GSD ac = GSD in scanned analogue cameras 
g = gain factor, g>l 
In general, it was noticed that digital images allowed 
stereoplotting of the same map scale using a GSD 1.1 up to 1.6 
times greater than the GSD of scanned analogue images. 
Map scale 
GSD ac [ml 
GSDdc fmj 
g 
1:500 
0,064 
0.010 
1.56 
1:1000 
0,106 
0,120 
1,13 
1:2000 
0,171 
0,200 
1,18 
1:10000 
0,423 
0,62 
1,46 
Table 6. Gain factor between scanned and digital images in the 
performed tests 
As shown in table 3 the gain factor is not a constant but changes 
according to the scale map and increase in value in smaller 
scale maps. The maximum reached GSD value for each map 
scale is reported in this table, according to the performed test; in 
particular, the reported GSD in 1:500 and 1:10000 map scales 
could be considered the maximum suitable values. 
In general, the g-value 1.6 must be considered a limit which is 
difficult to exceed because of the small size of the map entities 
to plot. On the contrary, g-values of about 1.1 or 1.2 should be 
considered very moderate. A compromise can be reached if a g- 
value of about 1.4-1.5 is considered. 
According to this issue, a new GSD has been proposed for each 
mapping scale (see table 7). This table, which summarize the 
conducted work, could be considered a valid aid to adapt 
Technical Specifications to the performances of new digital 
sensors. 
Map scale 
Scanned analogue 
camera GSD [m] 
Digital camera 
GSD [ml 
1:500 
0.06 
0.09 
1:1000 
0.11 
0.15 
1:2000 
0.17 
0.24 
1:5000 
0.32 
0.45 
1:10000 
0.42 
0.60 
Table 7. GSD comparison analogue - digital camera 
Starting from this value, it will be possible to determine the 
flight features of each digital camera, according to its internal 
geometry. An example is shown, considering the internal 
geometry of the 3-DAS-l camera, in table 8. 
A geometrical check of all the stereoplotted map entities has not 
been performed so far. In the future this methodology will be 
improved by checking, where possible, this geometrical 
precision in stereoplotted entities with the direct surveys using 
GPS-RTK techniques. 
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