| Abstract: | The Ordnance Survey (OS) has recently investigated the potential of orthophotography for revision of 1:2500 scale mapping following advances in technology since an earlier investigation in 1973. The results have been compared with stereoplotting on an automated workstation. The background to the investigation and the existing revision methods used for rural areas are described. Orthophotography was produced on a Zeiss 22 Orthocomp at 1:2500 scale using digital height model data supplied from contours (at a 5 m vertical interval) on 1:10000 scale mapping. A pilot block of 20 km2 was revised at Kingsbridge, south Devon to assess three levels of revision (local fit, part remedial, and full remedial), using three techniques (orthophotograph overlay, Stereo-orthophoto Plotter and stereoplotting instrument). The quality of the image of the orthophotographs was below that expected for rectified enlargements and the cost of orthophotograph production made the technique uneconomic compared with existing techniques. Orthophotographs were capable of improving the accuracy of revision mapping, but the most cost effective and accurate method was full remedial revision using a Kern PG2 automated workstation. |
