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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B6. Istanbul 2004 
  
First, the straight lines that represent the borders of the image 
format are obtained. Some authors (Cruz et al., 2000) use a 
linear regression of the edge points that define the image frame. 
In OIA program, the Hough transform applied to the straight 
lines extraction is used in order to determine which edge pixels 
belong to a specified frame edge. 
In order to simplify the edge location and reduce calculation 
times, an iterative procedure is carried out using the different 
images (with different resolution) that constitutes the image 
pyramid. The process begins with the small resolution image 
with the edges extraction and the results are improved 
according the resolution. Once the frame edges are extracted the 
corners of the image frame will be defined as the edge 
intersections. Finally, the IPP is obtained as the intersection of 
the diagonal lines (defined between opposite computed 
corners). The image x-axis is defined parallel to the upper 
extracted frame edge. 
  
  
  
Figure 7. OIA main display window (non-metric cameras) 
3.3 BUILDING. 
BUILDING is an application software for semiautomatic 
building prismatic modelling using Hough transformation 
(Figure 8). Indeed, this is a more complex photogrammetric 
process. 
Datos del MDE /MD' 
Ares Mínma (m2) : E 200 Resolución (m) 
Area Máxima [m2] Precision 
  
Altura Minima {m} : E384 
  
Dist de Apertura 
Figure 8. BUILDING program main display window 
BUILDING is organized in several steps: a) preparation, b) 
location, and c) extraction. 
The preparation step (figure 9) consists in the acquisition of the 
basic information required for the process. The basic required 
information are: a) digital image in which the building 
extraction process will be carried out (using this original image 
a gaussian image pyramid will be made); b) calibrated 
coordinated of the fiducial marks (from the camera calibration 
certificate); c) exterior orientation parameters; and, d) digital 
surface model in grid format (XYZ) stored in an ASCII text 
file. 
The XYZ data will be transformed into an image format in 
order to improve the required storage space. Finally, the 
automatic inner orientation of the image will be made using the 
OIA program. 
| IMAGES | DSM (ASCCI) 
Camera File 
Hough-Circles 
INNER O. 
Param. 10 
Param. EO 
ORIENTED IMAGES DTM (IMAGE) | 
  
Figure 9. Preparation 
The next step is the building location (figure 10). This step 
begins with the study area selection using the DSM. This zone 
will be studied using mathematical morphology procedures 
considering an approximation of the building characteristics