A procedure for map updating using digital mono-plotting
Aerial photographs can be used to produce and update terrain surface maps. This procedure, however, requires the use of expensive equipment which is not readily available to most offices which use such maps. Advances in computer science and the availability of low cost equipment for digitizing and digital processing of aerial photographs, allows for a wide range of applications for the production of cartographic information of the terrain surface by digital means, one of them being digital mono-plotting. This is the production of planimetric information of a terrain surface by direct vectorization. on a digital aerial photograph, using an image display for digitizing all significant features of the terrain, and afterwards performing an analytical transformation on those vectors in order to correct the deformations intrinsic to the aerial photographs. In the situation of non-flat terrain. a rigorous transformation has to be performed on the digitized lines (vectors), using colinearity equations based on control points of known coordinates and the digital elevation model (DEM) of the terrain. In such a way, deformations due to relief displacement and photographic tilt are corrected, obtaining a map free of deformations, at a known scale and referenced to a terrain coordinate system. To obtain the planimetric position of an image point on the terrain surface, the intersection point of the corresponding projective ray with the DEM of the terrain must be determined. In general, this is an iterative and time-consuming procedure. In this paper an alternative direct solution to this problem is presented with an example application. (C) 2002 Published by Elsevier Science Ltd.
mono-plotting digital elevation model (dem) digital orthorectification colinearity correction digital image