In: Paparoditis N., Pierrot-Deseilligny M.. Mallet C. Tournaire O. (Eds). IAPRS. Vol. XXXVIII. Part ЗА - Saint-Mandé, France. September 1-3. 2010 
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lies inside of plane polygon. If a pixel has assigned more than 
one ID, the closer plane is marked as visible. Based on this 
image it is possible to determine for each plane the fraction Oj of 
occlusion as follows: 
(1) 
where: 
n - number of occluded pixels in plane i, 
N - number of pixels occupied by plane i. 
Figure 1. A concept for texture mapping using texture qualities 
3.2 Texture resolution 
In nadir view the ground resolution of the images, usually 
expressed in ground sample distance (GSD), depends on aircraft 
altitude, digital terrain model and pixel size. Using oblique view 
the ground resolution depends also on the image coordinates. 
More specifically, objects situated at near range have higher 
resolution than objects at the same height seen at far range. In 
consequence, even horizontal faces don’t have an unique 
resolution. For storing the original resolution of the texture its 
resolution map need to be created. This original resolution of 
the texture depends on orientation of the face and the distance 
from the camera. In the Fig. 2 a situation is shown where the 
face (roof) is seen in far and near range. 
Figure 2. Image acquisition with oblique view 
We assume that this roof is a differential surface, is always 
oriented to the camera and the aircraft has a linear trajectory. In 
this way the changes in the resolution between far and near 
range can be investigated. The projection of this surface onto 
image plane is depicted in Fig. 3. 
Figure 3. Projection of a differential surface oriented to the 
projection centre 
The angles pi and P2 can be calculated by equation (2). 
/?, = arctg(tga-?Jj) -a fi 2 =a- arctgitga + 0) 
where: 
pp - pixel pitch 
/- focal length 
Therefore, the resolution of the differential surface along y-axis 
in camera coordinate system can be calculated as follows: 
cos(0 + a v ) 
r( y) = -7;—;— ——- [ pixel / m\ 
H(tgß u .+tgß 2y ) 
(3) 
where: 
r(y) -resolution of the along y-axis 
H - aircraft altitude above the differentia] plane 
9- inclination angle (pitch angle) 
(p- angular aperture 
Analogical, the resolution along x-axis can be calculated using 
equations (4).