MATCHING TECHNIQUES AND ALGORITHMS FOR SOME BASIC PHOTOGRAMMETRIC PROCEDURES IN THE LOW COST DIGITAL PHOTOGRAMMETRIC SYSTEMS

摘要

Two opposite solutions are available on the digital photogrammetric system market: high cost/performance solutions based on sophisticated ad hoc hardware (e.g. PHODIS ST by Zeiss, DPW 770 by Leica-Helava, etc.) and low cost instruments based on PC platforms (e.g. DVP by Leica), which offer poor performances and are only suitable for small scale, thematic mapping and educational purposes. A new class of professional instruments can be foreseen: digital instruments based on standard modular hardware and software, which fulfil the standard map production requirements at a reasonable cost and offer most of the advantages of the digital technique. Such instruments should be equipped by: 1. a scanning unit, possibly a low cost DTP scanner; 2. efficient calibration software that provides the corrected primary data from geometric (and radiometric) distortions; 3. the possibility of refining the human collimation on the rough level determined by the pixel size, using an efficient sub-pixel matching technique; 4. an automated DEM production procedure, for further orthophoto creation. The authors have implemented and tested the above mentioned basic procedures, in particular: 5. a calibration software for the DTP scanners; 6. a sub-pixel matching programme, working on line; 7.an automatic procedure for measuring the DEM heights, based on the VLL (Vertical Line Locus) principle. The algorithms and procedures are here described in detail and the practical results are shown in terms of quality and reliability.