541 
errors in Table I and appears therefore to be the limiting factor in the 
acquisition of the digital data bank information. As expected the standard 
error in the vertical identification of the boundary points was lower than the 
standard error in planimetric identification, and is exceeded by the rms 
vertical errors in Table I, derived for the tests with reduced X-parallax to 
height ratios. The advantages of improved image quality by the use of smaller 
X-parallax to height ratios in the generation of stereo-orthophotos must 
therefore be carefully weighted with respect to the resulting drop in vertical 
accuracy which may have a sígnificant effect on the final accuracy. 
CONCLUDING REMARKS 
The experience obtained so far in the pilot project has demonstrated the 
suitability and versatility of the stereo-orthophoto technique for the 
acquisition of cadastral information. It has been demonstrated that, for the 
type of information, to be collected for. the rural areas, the accuracy of the 
stereo—orthophoto system, presently in operation at IGAC, is adequate. The 
dominant source of errors in the system was found to be in the identification 
of parcel boundaries ín the photographic images. Additional tests are 
necessary to determine to which extent the stereo-orthophoto technique can be 
used to digitize the information for built-up areas and at which stage more 
accurate systems, such as the analytical plotter, will have to be used. 
The configuration of the present prototype system at IGAC is capable of 
processing and storing the amount of data required for a typical cadastral 
region in Colombia. Although aerial triangulation and the production of 
stereo-orthophotos and digital terrain models would remain to be carried out 
centrally at the head office in Bogota, the data acquisition at a regional 
level, particularly when based on the stereo-orthophoto technique, appears to 
be a logical and desirable solution. 
REFERENCES 
Gonzalez-Fletcher, A., "Modern Technology in Cadastral Operations in 
Developing Countries", the Canadian Surveyor, Vol. 34, No. 1, March 1980, 
pp. 54-64. 
IGAC, "El Catastro como Base para el Desarrollo”, Revista Cartografica 37, 
July 1980, pp. 59-73. 
Jaksic, Z., "On-Line Computational Photogrammetry in Geocoded Land 
Information Systems", Proceedings FIG XVIth Congress, Montreux, 
Switzerland, August 1981, pp. 510.6, 1-13. 
Jaksic, Z., van Wijk, M.C., "The Prototype Land Information System for the 
Cadastral Pilot Project in Colombia”, Proceedings Auto Carto Six, Ottawa, 
Ontario, October 1983, pp. 128-137. 
van Wijk, M.C.,  "Geometrical Quality of Stereo-orthophotos Produced from 
Automatic Image Correlation Data", Photogrammetric Engineering and Remote 
Sensing, Vol. 45, No. 10, October 1979, pp. 1365-1369. 
van Wijk, M.C., "Instrumentation for Land Information Data Acquisition Based 
on Stereo Orthophotos", Proceedings ISPRS Commission II Symposium, 
International Archives of Photogrammetry, Vol. 24-11, ISSN 0252-8231, 
September 1982, pp. 110-116. :