Comparison between two low cost photogrammetric systems: The analytical instrument Adam ASP2000 and the digital photogrammetric station DVP

Abstract

The creation of the National Cadastre’s map, part of which is the forest cadastre (according to the decision of the Ministry of Agriculture No 99580/506 from 1 July 1999), is based on law 266/1998 ‘National Cadastre and other provisions’ and forecasts the use of photogrammetric methods. The changes in land use, and the stretches of mountainous and semi-mountainous abandoned land are represented on these maps. The photogrammetric community is experiencing a transitional period from the analytical to the digital era. This transition is met with prudent enthusiasm, and care as to which digital systems may replace the analytical ones and under what circumstances this change will take place. This paper endeavours to answer such a question. A complete and fully documented answer lies of course, outside the limitations of this project. Here, however, a comparison was attempted between a contemporary analytical photogrammetric instrument and a digital photogrammetic system, which are both of relatively low cost. This choice was made in order to enable the market in this country to assess the limitations and possibilities of such systems, in view of the large-scale cadastral surveys. Therefore, this comparison is not only confined to accuracy, but touches upon other issues, such as reliability, user friendliness and efficiency. There are many factors, not to mention errors, in the photogrammetric procedure. There main causes are the operator, the instrumentation used and various unpredictable factors. The area of study and stereopairs thatwere usedwere chosen so that a reliable terrestrial survey would be available for the purposes of control. A rural forest area and a forest area of Taxiarchi–Vrastamon were selected. For these areas, stereopairs and related diapositives were available at the scale of 1: 20000. They were taken from an E.E.C. GR80-3 (c = 152.25 mm) aerial survey camera with an overlap of 65%. The same control points were used for the orientations on both the analytical low cost system and the digital low cost system. The analytical low cost system is a more reliable instrument than the digital low cost system, because both its repeatability and accuracy are better.