DTM Applications Presentation

Ortho-photo generation DTM Applications Ortho-photo generation Volume computation Deriving watersheds Fire risk assessment Placing pipelines

DTM Applications Ortho-Photo Generation Maps & Images Orthogonal projection. Uniform scale. No relief displacement. Perspective projection. Non-uniform scale. Relief displacement.

DTM Applications Ortho-Photo Generation Relief Displacement VS.

DTM Applications Ortho-Photo Generation Ortho-Photo Characteristics: Relief displacement free image. Image which has the same characteristics of a map. Orthogonal (parallel) projection. Uniform scale. No relief displacement.

DTM Applications Ortho-Photo Generation Ortho-photos are generated from aerial photographs and satellite images through a process known as ortho-rectification. Polynomial rectification Differential rectification. Central projection of the photograph Orthogonal view of the ground Ortho rectification removing the distorting effects of tilt and terrain relief

Ortho-Photo Advantages 1 They have the same characteristics of a map but with more features. 2 The user can draw lines and measure distances without the need for stereo-plotters. 3 Cheap alternatives for maps (for developing countries). 4 They can be generated automatically. 5 They are important for GIS applications.

DTM Applications Ortho-Photo Generation Ortho Photo & DTM

DTM Applications Volume Computation From Contour Lines From Grid

DTM Applications Volume Computation: From Contour Lines Split the ground along the contour planes into a series of horizontal slabs. Each slab being considered as a prismoid with the height equals the contour interval and end areas are the areas enclosed by the contour lines.

DTM Applications Volume Computation: From Contour Lines The volume of the prismoid between the two contours ci and cj: General Formula:

DTM Applications Volume Computation: From Grid The volume within each DTM cell is computed as: General Formula:

DTM Applications Volume Computation and Cut/Fill Applications

DTM Applications Watersheds The Question If a drop of water falls here, which collection area (or catchments) will it end up in? Watersheds are particularly important to ecological and hydrological applications. A raster DTM contains sufficient information to determine general patterns of drainage and watersheds.

DTM Applications Watersheds Algorithms to determine the flow direction can use one of the following search methods: Assume only 4 possible directions of flow Assume 8 possible directions .

DTM Applications Watersheds: Example

DTM Applications Determining a Drainage Network

What If Applications What-if applications makes use of the DTM derivative as well as other data sources to create a virtual dataset that answer specific question: For example, show all areas between 1200 and 1500meters altitude with less than 15% slope gradient. The key to what-if processing is to be able to: Express the problem in terms of what-if processing of your data Work with algorithm formula, kernels, and transforms to achieve the results.

DTM Applications Highlighting Area of Fire Risk The direction of prevailing hot winds The relative relationship between the surface slope and the hot wind direction The vegetation biomass on those slopes Aspect Slope Vegetation Mass

DTM Applications Highlighting Area of Fire Risk In this case, we would like to express fire risk as a number from 0 to 1; with “1” being higher fire risk. (SLOPE_DEGREES/90) (1-(ABS(180-ASPECT)/180)) ((NDVI + 1)/2)

Normalized Difference Vegetation Index (NDVI) NDVI = (NIR — VIS)/(NIR + VIS) Calculations of NDVI for a given pixel always result in a number that ranges from minus one (-1) to plus one (+1). Non-green leaves gives a value close to zero. NDVI close to +1 (0.8 - 0.9) indicates the highest possible density of green leaves.

Slope & Aspect Maps Slope Aspect is the tangent of the angle between: The surface normal, and The zenith direction. is a measure of the steepness of the surface patch. Aspect is the azimuth of the projection of the surface normal onto the XY-Plane. is a measure of the orientation of the surface patch in space. 2nd derivative of the DTM of the slope 1st derivative Describes the curvature of the terrain

DTM Applications Highlighting Area of Fire Risk Adding these three factors together and dividing by three: This will result in a fire risk layer, with 1 as high fire risk, and 0 as low fire risk. We would use the final transform in the layer to scale this number, to color code the fire risk map, using a pseudo-color layer.

DTM Applications Highlighting Area of Fire Risk

DTM Applications Placement of Pipelines In this example, we are interested in highlighting any area of the DEM that meets the following criteria: Slope is less than 15%; DEM heights are within the range 1200 meters to 1500 meters; In this example, the generic formula would be: IF SLOPE<15 AND DEM_HEIGHT>=1200 AND DEM_HEIGHT<=1500 THEN 1 ELSE NULL

Elements of Digital Terrain Modeling

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