International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B4. Istanbul 2004 
  
same. Thus, no extra work is required to scale, orient, or wrap 
the new texture to fit the original one, when the merging 
process takes place. Small mismatches may, however, arise if 
the perspective views of stations over the area of interest are too 
different. Therefore, when examining the low resolution 
textures a station should be selected that not fills the affected 
area appropriately, but also does not result in large 
discontinuities in the final texture. The process of merging 
textures can be done in two ways described below. 
3.1 Pick and paint 
Some image processing packages like Photoshop TM allow 
painting a copy of an image onto another image interactively. 
For this, samples from a source texture are Picked and Painted 
onto the same area on the other texture. For convenience, the 
original texture is defined as the destination, while the one 
created from an individual neighbouring station is taken as the 
source. 
The Pick and Paint process involves positioning the cursor over 
the area of interest in the source texture and picking a sample 
point. The sample point is the location from which the image 
will begin to be duplicated as Painting operation takes place in 
the destination texture. The cursor is then pressed at the same 
point in the destination texture and is dragged to Paint the 
sampled texture. The process is continued until the whole 
unwanted area of texture is filled in with the source samples. 
The resulting texture is saved and a new texture taking parts 
from each texture is created. 
3.2 Forcing ATPT 
This approach is more automated compared to the Pick and 
Paint method. Having defined the station at which the affected 
area has to be produced, the image coordinates of the affected 
area along with the station identification are introduced to 
ATPT. While processing the texture points, the ATPT uses the 
images of the given station to define the pixel value of the 
point. The rest of the texture creation process remains the same 
as that described before. 
Compared to the Pick and paint method, Forcing ATPT is more 
convenient and requires less interaction while the former is best 
used to demonstrate the merging process. However, the Pick 
and paint method is more flexible and allows the affected area 
to comprise more irregular shapes. 
3.3 Examples: a missing image 
In an experience, textures obtained from two different stations 
were visually investigated. Despite having a good view over the 
facade area, the first station failed to fill the upper right part of 
the texture (Figure 7-a) This part was missing due to an 
internal error in the data capture unit. The error was, however, 
only realised later when the data capture phase had finished. 
Thus, it was decided to use images from another station to fill in 
the gap instead of recapturing the data. 
Fortunately, the second station, besides covering the missing 
area, had a good orthogonal view of it (Figure 7-b). Figure 7-c 
shows the texture from the first station, the missing part of 
which is filled in using the texture from the other station. 
440 
  
(b) 
  
Figure 7. A texture merging example to fill missing part 
3.4 Examples: an occluding tree 
Here an example is given to show how an occluding tree can be 
removed from a texture. Figures 8-a to 8-c show textures that 
all see a building wall from different stations, of which (a) has 
the most orthogonal view over the area of interest. This 
texture, however, includes a big tree that occludes parts of the 
building facade. Comparing the other two textures, it can be 
seen that (c) does not include the image of the tree and has a 
good orthogonal view over the tree area. This texture was 
therefore selected as the source, from which samples are taken 
and painted over the tree area on (a) For a better 
demonstration, the merging process was done in two steps. 
Figures 9-a and 9-b show the original texture with the tree 
partly (a) and completely (b) removed using the Pick and paint 
method. As the textures are all created for the same face and at 
the same resolution, they fit well leading to almost a 
homogeneous texture. 
A further enhancement was to improve the geometric quality of 
windows on the texture. As can be seen, the windows on the left 
side of the final texture are slightly stretched out due to 
perspective distortions. The Pick and paint method can thus be 
used to improve the quality of the texture reducing the 
perspective distortions. Figure 10-a shows the final texture, on 
which some of the windows on the left side are stretched. 
  
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