Ermes, Pierre 
  
The simultaneous estimation of the exterior orientations and the pose and shape of the models changes the workflow 
compared to the separate triangulation and model-measuring stages. In the pilot project described in the next section we 
choose a distinct model from which at least one dimension was known. The pose of the model and the dimension are set 
to specific values so that the model is positioned in object space with a known scale. 
The exterior orientation of an image containing this model can now be estimated. An operator provides an approximate 
value for the orientation, either by entering the numeric values of the orientation, or by interactively choosing a 
viewpoint in a 3D viewer (like a VRML browser). In this viewer, the image is projected in the background while the 
models are displayed using a hidden-line projection. Starting with the approximate orientation, the operator makes more 
precise measurements on the displayed model. Using these measurements, an accurate estimate of the exterior 
orientation is computed. This is done for all the images that show the selected model. Other models can be measured 
using this set of images which gives the opportunity to orient more images that show these newly measured models. 
After which more images can be included in the measurements, and so on. Once all the measurements are complete, a 
global bundle adjustment is computed in which all model parameters and exterior orientations are estimated. 
This method uses parameterized CSG models as the connecting entities between images in contrast to the use of points 
in a triangulation-based bundle adjustment. 
6 EXPERIMENTS 
A pilot project was undertaken at a gas exploration site of the NAM in Tjuchem, the Netherlands. The recorded area 
comprises a gas-drying unit, which measures about 30x30 square meters and has a maximum height of about 5 meters. 
In about 3 hours 102 images were recorded on site using a Kodac DCS420 camera (1012x1524 pixels). See the images 
in Figure 4 for an overview of the installation. The interior orientation and lens distortion of the camera are known. 
Several dimensions of the installation, such as radii and lengths of piping elements, were tape-measured. 
The exterior orientations were obtained using the model-based bundle adjustment described above. The measurements 
started with the large box in the foreground of Figure 4a. The orientation of the box in the object coordinate system is 
constrained so that one corner of the box coincides with the origin and the box is aligned with the object coordinate 
axes. The length of the box (10645mm) was measured using a steel tape and the size of the model was constrained to 
that value. Starting with the box, all the images that show this model could be oriented. After that the procedure 
described in the previous section was followed. 
  
  
Figure 4. Images of the gas-drying unit. 
Only some (36) of the recorded images were used for the measurements. The installation was modeled using 218 CSG 
models, which were built with a total of 288 geometric primitives. Figure 5 shows the reconstructed model. The 
primitives and the image orientations are parameterized with a total of 2706 parameters. The operator measured 2744 
points on model edges and applied 1487 constraints. 313 extra constraints were included for constraining the lengths of 
the rotation-parameter vectors, giving a total of 4544 observation equations. 
The measurements took approximately 2 weeks, although one must keep in mind that the current application is a first 
prototype. Improvements to the user interface can still be made to increase the efficiency of the process. Assuming an 
accuracy of 1 pixel of the measurements by the operator, the estimated accuracy in object space is approximately 5- 
  
220 International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B5. Amsterdam 2000. 
  
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