ADVANCED PHOTOGRAMMETRIC METHODS IN CADASTRE 
INCLUDING STEREO-ORTHOPHOTO TECHNIQUES* 
  
  
Z. JAKSIC 
Photogrammetric Research 
National Research Council, Ottawa 
The orthophoto techniques are well-known and have already found extensive application 
in topographic mapping as well as in cadastre (e.g. Radlinski 1968, Dubuisson 1968, Johansson 
1968). The orthophotos with their characteristic suitability for semi-automatic and automatic 
production and their preservation of the wealth of information recorded on photographs with quite 
adequate preservation of geometrical fidelity, have made a significant impact on the way of think- 
ing about modern surveying and mapping problems, As in photomaps derived by rectification, the 
main shortcoming of orthophotos is the absence of the third dimension, The development of the 
stereo -orthophoto techniques eliminated that deficiency. (Blachut and van Wijk 1970). Technically 
speaking a stereo-orthophoto is a stereopair consisting of an image in orthogonal projection and 
one in a parallel projection, with the projecting rays inclined with respect to the projection plane, 
The general topographic features and boundaries are presented consequently in an axonometric 
stereoscopy and details such as houses and trees are presented in perspective stereoscopy. The 
stereo -orthophotos can be produced from stereograms on somewhat modified but essentially the 
same type of equipment as the one normally used for production of orthophotos, With modifica- 
tions allowing for sequential or simultaneous production of both the orthophoto and its stereo-pair 
(or stereo-mate), analog, hybrid and analytical instrumentation may be used, with optical or 
electronic scanning techniques as well as gestalt techniques, For the time being economically 
satisfactory results can be expected from hybrid instruments, with optical scanning and the faci- 
lity for simultaneous production of both images, such as the Orthocartograph whose prototype is 
presently being built in the Photogrammetric Research Laboratory of the National Research Coun- 
cil of Canada (Blachut 1971), 
Once produced the stereo-orthophotos represent a three-dimensional pictorial record 
which can be a base for any type of graphical or numerical data acquisition, The Stereocompiler 
a simple and economical instrument for the exploitation of stereo-orthophotos in a variety of 
modes and applications was built in the Photogrammetric Research Laboratories of the NRC of 
Canada (Fig. 1). The main construction element of the Stereocompiler is a carriage supporting 
both images of the stereo-orthophoto pair, This carriage is moving over a glass plate on three 
air-bearings. The simple viewing optical trains are fixed, The stereo-mate can be moved rela- 
tive to the orthophoto in the X-direction by a stepper -motor activated with a pedal, These move- 
ments allow for the setting of the measuring mark on any point in the model space and consequent - 
ly for plotting of planimetry and contouring. There is an option for three linear encoders, with 
corresponding counters which permit recording of model coordinates (Fig, 2). For direct plotting 
a scribe sheet or a transparent drafting sheet may be put directly over both images. This enables 
the operator to view the result of plotting directly, while observing the stereo-model, This is an 
extremely important real-time feature of the stereocompiler, equally advantageous in conven- 
tional plotting or continuous digitizing (Jaksic 1971), The accuracies obtained in the first experi- 
ments indicate a mean square error in the determination of the coordinates of the order of * 40 um 
at the original photo scale, It is expected that with some improvements in the production of stereo- 
mates, the accuracies in elevation will be of the order of * 20 um at the original photo scale 
(Blachut 1971). If the accuracy limitations of orthophotos and stereo-orthophotos are acceptable 
for a cadastral system and the sub-systems of a larger national information system, then the 
Stereo -orthophoto technique offers a number of advantages over all the other photogrammetric 
techniques (Fig. 3). 
  
* Presented at the First Pan American Conference on Cadastre, Caracas, Venezuela, 
November 14-20, 1971. 
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