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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B4. Istanbul 2004 
  
e Test on possible parallelism to the next street. If it is 
possible within a threshold value, parallelism is 
reconstructed by rotating the building round the center 
of mass. 
e If the object is significantly changed after the tests 
above, original area, center of mass and direction 
(bearing of the longest edge) are reconstructed by 
rotating, scaling and moving. 
The threshold values, which are entered by user, for the tests 
above play an important role for the performance of the 
program. These certainly depend on the scale. Program default 
values-are determined at the 1:1000 scale. 
Three properties of buildings should stay unchanged after 
processing. 
e Area 
e Center of mass 
e Direction of the building (bearing of the longest edge, 
figure 1) 
These parameters are saved before processing. 
  
Figure 1. Direction of the building 
In figure 2, the flow chart of the program is shown, where the 
processes and strategy of BUHOM are depicted. 
2.1 Right Angle Adjustment 
The right angle adjustment process is relatively simple. 
Building objects are processed independently from each other. 
Starting from the first edge of the object, angles between edges 
are calculated and determined if these may be right angles. In 
figure 3, for instance, if the angle a approximates to a right 
angle within a threshold value, the edge 2-3 is rotated around 
the middle point of the edge. So the edges 1-2 and 2-3 are 
perpendicular to each other. The examination of the edges 
continues until the edge 8-1. 
Another approach would be the rotation of the edge around the 
starting point (point 2). It is not preferred in the program 
development because we assumed that such rotations cause 
more change in the location of building. 
If two edges perpendicular to each other, following condition 
must be fulfilled. 
  
E y= ome) nd m0 (D 
(5 7x, ) A3 
If d #0, the deviation from the right angle is following. 
2 
5 
Get the object 
Small area test 
: = 
n 
Test on identical 
points 
  
  
  
  
  
  
  
  
Erase point or 
| | align point 
Self-cut test [| 
Intersection 
  
  
  
  
  
  
  
  
  
Determination of the 
significance of point 
  
  
  
Test on insignificant 
points 
  
  
  
  
  
Center of mass, direction 
[| and area calculation, 
control of the parallelism 
to street 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
Calculate building ~ Determination of 
properties possible right angles 
Right angle 
adjustment Rotate edge 
Calculate building 
properties 
y EE Em 
re thes 
objects? 
y n Delete old object, save new 
object 
Recontruction of the E ee 
Create report original building 
properties 
Figure 2. Flow chart of the program BUHOM 
  
  
  
  
  
A 2. 3 6 7 
P 
5 
8 
© 
o 4 5 
- : 
  
  
  
Figure 3. Processing of edges at right angle adjustment 
» 14mm 
dà - tanda - ———2—2- 
(2) 
Hy, — Hy 
If dais smaller than the threshold value (for angles), it is 
allowed to rotate the edge 2-3. The threshold value selected by 
the user determines the degree of the shape changing of the 
whole process. 
2.2 Insignificant Points on the Object Boundary 
On the boundary (contour) of building objects there are points 
that lie approximately on the same straight line with previous 
and next points. In figure 4, for instance, point 2 is such a point. 
Such points can be identified examining the angle da (figure 
4). If it approximates to zero, point 2 can be considered as