Figure 2. Result of edge detection to locate 
the occluding edges of a pipe. 
  
The first step in this process was to increase the 
functionality of a primitive fitting program (geofit), to fit 
not just 2D and 3D geometric primitives to swarms of 
points, but cylinders to a selection of tangent planes. Data 
is supplied to this routine from HAZMAP, where operator 
directed edge detection filters are applied to the digital 
images in order to derive points along the occluding edges of 
a cylinder. 
These points are passed to geofit in two stages: the first 
determines the equations of the tangent planes -Figure 2 
shows some results with the light crosses being image 
points which have been rejected as outliers; the second 
determines the best fit cylinder to the observed tangent 
planes. The resultant cylinder is then injected into the 
HAZMAP images, where it may be manually extended to fit 
the observed pipe and exported to the CAD model. 
The modelling process has now been further automated by 
using the cylinder projection equations. This is done to 
either update the parameters of a cylinder from an existing 
CAD model, or to generate a new cylinder having first 
roughly positioned an injected solid using several 
convergent HAZMAP images. The parameters of this 
cylinder are used, together with the spatial relationships held 
in the HAZMAP database, to select a group of images in 
which the pipe in question is likely to appear. The equations 
of the occluding edges of the cylinder, as viewed in each of 
these images (Figure 3), is then determined. These equations 
are used to direct the edge detection routines, and the results 
are processed as before, to generate the parameters of the 
cylinder for export to the CAD model. 
  
Figure 3. Cylinder projected into nine images of a pipe, five of which are used to update the pipe location. 
288 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B5. Vienna 1996 
A deriva 
outlined 
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Bell, RJ 
Geometr 
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Bowyer, 
Computi 
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modellir 
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Remote 
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Petsa, E 
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Photogr