International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B4. Istanbul 2004 
  
necessary sections have to be extracted, and an additional side 
strip of 300 m is added to avoid border effects. 
The buildings of particular monumental and architectonical 
importance require additional refining editing and 
photogrammetric restitution procedures. In these cases, the 
building coverage is modelled with horizontal surfaces 
(geometrically identified with a contour polyline and height 
point), or plane surfaces oriented in the space. Some examples 
are shown in fig 12. 
  
Figure 12: Examples of 3D representation of monumental 
buildings 
6.2 DDTM Generation 
A file containing data on the processing (such as the 300 m 
border strip, the chosen DDTM with pixel size of 20x20 cm’, 
the codes of the entities involved and the interpolation type, 
bilinear) was compiled for each map. 
The DDTMs were also produced as georeferenced digital 
images. In this way, their correcteness could be tested by 
overlaying them on the digital map. 
A digital grey-scale image (darker greys mean lower heights) of 
a DDTM in figure 13 is shown for an entire map (almost 
7300x6300 pixels, corresponding to almost 45 Mb of memory 
allocation), generated by a standard PC (Pentium 4, 2 Ghz, 1 Gb 
RAM). in about one hour. 
  
Figure 13: DDTM of the entire cartographic map 
6.3 True orthophoto generation 
A file for each map containes data on the size and position of 
the map, the name of the corresponding DDTM file, 
interpolation type (nearest neighbour), and the orthophotc 
resolution on the ground (i.e. for example 20 cm). 
The generated orthophotos were checked by overlaying them or 
a digital map, to find possible imperfections. To correct some 
residual errors, and to improve chromatic equalization, a post 
editing phase was made using Adobe Photoshop. 
An entire orthophoto map (near 6600x5500 pixels, that means 
208 Mb in True Colour mode) is shown in figure 14a that was 
generated in almost 2 hours with a standard PC (pentium 4, 2 
Ghz, 1 Gb RAM), with a detail (figure 14b) overlayed with 
cartography (14c). 
  
Figure 14: example of an ortophoto: an entire map (a), a portion 
(b), the same portion overlayed with cartography (c). 
Some other important examples of monumental buildings 
extracted from the historical centre of Turin are shown in figure 
15. 
The image files that were obtained were saved in JPEG format, 
with a relative georeferencing file (Jgw): in this way they can be 
inserted with an automatic georeferentiation into any GIS 
software, as displayed in fig. 16. 
7. ORTHO SOLID IMAGE 
The image of a digital true orthophoto and the height values 
derived from DDTM can be merged in a new product: the ortho 
solid image, a simple extension of the 3D solid image (Bornaz, 
Dequal, 2003). In this case, for each pixel of an ortho solid 
image, it is possible to record: 
e 3 colour values for the true colour image (RGB) 
extracted from the orthophoto and memorized in 3 
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