الفهرس 
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Abstract
Surface modeling is a general term, which is used to describe the process of representing a physical or artificially created surface by means of a mathematical expression. Terrain modeling is one particular caregory of surface mpdeling which deals with the specific problems of representing the surface of the earth.
The digital terrain model DTM is simply a statistical representation of the continuous surface of the ground by a large number of selected points with known X,Y,Z coordinates in an arbitrary coordinate field system.
In this context, agird base digital terrain models were derived from both digitized contour lines and digital image matching techniques. The first was obtained by interpolating with a high quality algorithm scanned and vectored contours of existing topographic sheets. The second was extracted from scanned aerial photogaphic sheets. the second was extracted froj scanned aerial photographs using a soft copy photogrammertic system (HELAVA).
By comparing each DTM with a third terrain model generated from traditional ground surveying technique, as three different data sources. then investigate the accuracy of each DTM generated from each data source.
The obtained results showed that, the DTM generated from the ground surveying data is the best one, followed by that generated from photogrammertic data, finally, the DTM generated from the contour maps is coming at the end.
I.E, we can say that the best DTM data source is the ground surveying data, then photogrammertic data, finally the existing topographic maps data, as arranged in an descending order according to the achievable accuracy. The worst results are coming from the existing topographic maps data source.This is due to the production method of this maos.The created contour maps are depending on forming a maodel coinsides with the surface of the earth and tracing this model, existing any distortion in forming this model for any reasons, causes to defect in producing the contour maps, and the created DTM from this maps.