International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B7, 2012 
XXII ISPRS Congress, 25 August — 01 September 2012, Melbourne, Australia 
  
  
0 PS per 1000 m? 9 
Figure 6. Map of PS densities. The colours code the number of PS per 1000m?. The shown prismatic building models have been 
used to calculate the volume of the building. 
windows with a broad windowsill while a flat wall will host few 
to no PS. 
Furthermore the geometric configuration is a very important 
factor. Since the majority of the PS is usually located at the 
facades, it is very important if a facade of the building is visible 
to the sensor. But even the exact orientation of the facade with 
respect to the sensor plays a major role, because the signal 
reflected at facade structures may strongly depend on that. 
Finally, miscellaneous circumstances may lead to low PS 
densities for buildings. Even though its facade and roof 
structures should give rise to a plethora of PS, a building could 
for example be under construction for some time while the stack 
is being acquired, which would lead most likely to a loss of all 
PS. 
4.1 Areaa 
In area "a" the dependence of the PS density from the facade 
and roof structures can be easily demonstrated. Figure 7 shows 
the PS assigned to the buildings and the corresponding densities 
in a close-up. While parts of the three buildings in the back may 
be occluded, the two buildings in the front are completely 
visible to the sensor. Nevertheless their PS density differs 
considerably. 
The orange building exhibits a density of 2.4 PS per 1000m’ 
while the red one hosts just 1.4 PS per 1000m’. This is even 
more pronounced for the dark blue building, which may be 
occluded to a small extent, but shows a density of roughly 7.5 
PS per 1000m°. In Figure 8 an oblique view aerial image of the 
scene is shown (© MS-Bingmaps). It is easy to see that the 
buildings feature a quite different facade construction. 
Obviously the facade of the building with the lowest PS density 
does not accommodate any structures leading to PS, which can 
be easily checked by the PS distribution shown in Figure 7. In 
clear contrast the orange and dark blue buildings are heavily 
populated with PS at the facade, which may be induced by the 
window structures. 
4.2 Areab 
The dependence of the PS density on the geometrical 
configuration can be very well demonstrated with the building 
complex encircled by rectangle b. 
  
Figure 7. PS density in test area "a". It is very conspicuous that 
one of the building (front right) exhibits a quite low PS 
density, while all others host a lot more PS. The reason for that 
is the different facade structure.