1. SaMeHFor Egyptian Cement Company1 2. Digital Terrain Models Dr. SaMeH Saadeldin Ahmed Assistant professor of Mining and Environmental Engineering Email: dr_sameh_mining04@yahoo.com A short course for Egyptian Cement Company (ECC) April, 2005

2. SaMeHFor Egyptian Cement Company2 Outlines 1.Definition 2.General Outlines of DTM 3.Sources of DTM 4.Principles of DTM 5.Interpolation of DTM 6.Accuracy of DTM 7.Applications

3. SaMeHFor Egyptian Cement Company3 1. Definition A Digital Terrain Model (DTM) may be defined as “ a numerical description of irregular as well as regular surface, based on the measurement of discrete points of this surface together with the corresponding interpolation rules”.

4. SaMeHFor Egyptian Cement Company4 2. General Outlines of DTM Two different aspects can describe the properties of DTM: 1) Method of Sampling 2) Method of Reconstruction In general, DTM is composed of sampling points data together with the interpolation rules.

5. SaMeHFor Egyptian Cement Company5 Terrain Classification Terrain Classification The basic data sources of DTM are terrain itself, its photogrammetric model as existing topographic maps for sampling. The classification can be approached in three different ways, namely qualitative, quantitative and mixed.

6. SaMeHFor Egyptian Cement Company6 a. Qualitative Classification Where visual inspection and interpretation of the terrain in question is the dominant factor, the approach necessitates that persons who carry out such classification should be highly skilled and well experienced. Disadvantage its outcome differs from person to person.

7. SaMeHFor Egyptian Cement Company7 b. Quantitative Classification As the title suggests, it is based on computing some parameters by which the class of the terrain is determine. So far, a fully quantitative method is not available.

8. SaMeHFor Egyptian Cement Company8 c. Qualitative- Quantitative Classification this is the most feasible method where the two previous methods are combined. The parameters of classification are: 1.Shape of profiles 2.Amount of local relief 3.Slope gradient 4.Number and length of break lines 5.Degree of roughness

9. SaMeHFor Egyptian Cement Company9 Sources of DTM Direct measurements on photogrammetric stereo-models. Ground surveying. Existing topographic maps. Existing orthophoto maps superimposed with contours. Profiles as a by-product through the production process of orthophoto. Stereo orthophoto. Radar and leaser altimeters carry in aircrafts & spacecrafts.

10. SaMeHFor Egyptian Cement Company10 Principles of DTM Measurement of elevation data should be taken in an efficient manner. The digital elevation model should be constructed by as small number of points as possible. The digital elevation model should approximate the terrain topography in a sufficiently high accuracy. The computation of interpolating point elevation should not demand too much time. The DTM should be suitable for elevation computation.

11. SaMeHFor Egyptian Cement Company11 Measuring Patterns Recording along closely spaced profiles. Scanning along contours and/or terrain break lines. Recording by regular point grids. Recording by irregular points grid or random points. Recording by regular point grids supplemented with break points. Recording by cross sectioning.

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13. SaMeHFor Egyptian Cement Company13 Interpolation of DTM Interpolation is the method of the reconstruction of the surface from the sampling points of terrain. Figure (2.2-a) shows the concept for definition of interpolation Figure (2.2-b) shows interpolation and filtering.

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15. SaMeHFor Egyptian Cement Company15 Accuracy of DTM The following are the main factors influencing the accuracy of digital terrain models: Density of reference points Distribution of reference points Type of terrain Accuracy of editing Accuracy of the measure: – The source of the reference points. – The experience and the skills of the operator.

16. SaMeHFor Egyptian Cement Company16 Applications of DTM the major applications of DTM data have covered the fields of design and planning of civil engineering projects highway projects, automated cartography, land use, soil classification, simulation studies, navigation and geographic studies.

17. SaMeHFor Egyptian Cement Company17 Thanks for your attention