The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B4. Beijing 2008 
well known, these cameras have different internal geometries 
(frame camera and pushbroom) and, as such, they have been 
considered representative of all digital cameras actually on the 
market. Furthermore the performed analysis has considered 
different flight images, acquired at different altitudes and over 
different kinds of landscape, in order to obtain the most 
complete set of data possible. This analysis considers from 
1:500 to 1:10000 map scales. A complete analysis of smaller 
scale maps cannot be performed considering only aerial sensors. 
It is necessary to considers also satellite ones (Boccardo et al., 
2005). 
The technical features of the sensors and available flight 
features are reported in the following table. 
Sensor 
Internal 
geometry 
f 
[mm] 
Flight 
height 
[m] 
Nominal 
Scale 
1: 
GSD 
[m] 
ADS40 1 st 
Pushbroom 
62.8 
6000 
100000 
0.62 
ADS40 2 nd 
Pushbroom 
62.8 
2000 
32000 
0.1-0.2 
UltraCamD 
Frame 
101.4 
900 
9000 
0.08 
DMC 
Frame 
120 
1200 
10000 
0.12 
3-DAS-l 
Pushbroom 
110 
900 
8000 
0.08 
Table 1. Available flight features 
The technical specifications in map production usually define 
the main features of photogrammetric flights in order to realize 
a digital map at a certain map scale. However these 
specifications refer to analogue cameras and consider these 
cameras equivalent to digital ones. For this reason, starting from 
practical equations and custom usage adopted in analogue 
flights, new practical equations for digital flights are presented. 
The used methodology to achieve these results is described step 
by step in section 2. 
In the performed tests, Ground Sample Distance was considered 
the Fundamental parameter in the flight specifications for 
digital cameras (Casella, 2006). Each digital camera in fact has 
a different internal geometry and it is actually impossible to 
find a “standard” for digital cameras. For this reason, the 
comparison was performed considering comparable flights with 
the same value for this parameter. The GSD of analogue images 
was obtained scanning these photos with a 20 pm pixel size 
because, with a smaller pixel size, no more details can be 
identified and accuracy is not appreciably improved (Jacobsen, 
2007; Lingua et al., 2007; Perko et al.,2004, Baltsavias, 1999). 
Finally the achieved conclusion are presented in Section 3, and 
a new table is proposed which relates the map scale to the GSD 
of digital photogrammetric flights. 
2. TESTING METHODOLOGY 
The traditionally nominal scale of analogue camera images is 
linked to the achievable map scale through practical equations 
and tables (Italian Geodetic Commission, 1973; Kraus, 1993). 
As known analogue cameras have reached a certain “standard” 
in internal geometry. As a consequence, considering a focal 
length of 150 mm (wide-angle camera), it has been possible to 
link a GSD (obtained by scanner) to a nominal scale and, 
through these tables (Italian Geodetic Commission, 1973), to an 
achievable scale map, as shown in figure 1. 
The equivalent GSD and the requested accuracy for each map 
scale is shown in figure 1. As shown, the Ground Sample 
Distance and accuracy differs by a non constant value: in some 
ways, handiness of interpretation influences the GSD size at 
large map scales (particularly in 1:500 and 1:1000 map scales) 
and the difference between these parameters decrease. 
The established link between GSD of (scanned) analogue 
images and the achievable map scale was used as a starting 
point. In other words, available digital flights were initially 
analyzed considering cartographic details required at a map 
scale with the same GSD; then the evaluation as to whether a 
larger scale was achievable using the same digital images was 
performed. As already proposed in [Giulio Tonolo et al., 2007] 
and in [Lingua et al., 2007], particular attention was paid to the 
ease of interpretation of the map entities which are required in 
Technical Specifications (at different scales) for map 
production, verifying whether it was possible to recognize and 
plot these details. In particular, the required map entities were 
detected in reference to the INTESA GIS technical 
Specifications which are the Italian application of the European 
INSPIRE Directive. 
Figure 1. Scale map and GSD in scanned analogue Cameras 
The map entities were analysed and judged for each available 
flight. This work was summarized in tables. An example is 
shown in the following in table 2. 
In order to define an achievable map scale for each flight, the 
requested map entities were initially grouped into 7 different 
levels (e.g. roads, buildings, etc.): for example, streets and 
pavements were inserted into the road category, rivers and 
channels in the water category, and so on. 
Then, in each level, the entities were classified in three 
different groups: 
• group A: it was possible to plot the entity; 
• group B: the entity was visible on images, but it was 
not possible to plot it; 
• group C: the entity was not neither visible. 
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