Chapter 9a

Chapter 9Digital Terrain Modeling

Definitions ►

Digital Terrain Modeling: concepts and techniques of acquiring and using digital elevation data.

►

Digital Terrain Data Sampling: structuring and acquisition of digital terrain data by photogrammetric, cartographic, and field survey techniques.

►

Digital Terrain Data Processing: the manipulation of digital terrain data to ensure their usability by GIS.

►

Digital Terrain Data Analysis: involves the use of algorithms and procedures that turn digital terrain data into useful geographic information.

►

Digital Terrain Visualization: Development of algorithums and methods that will allow the effective display of the terrain to assist in spatial problem solving and decision making.

DTM ► The

concepts of DTM are no longer just used for topography.

► Now

used for climate, meteorology, pollution, land cover, natural resources, distribution of socioeconomic variables.

► Common

surfaces.

thread? It’s 3D continuous

Figure 9.1

Approaches to Digital Terrain Data Sampling ► Two

basic approaches: systematic and adaptive.

► Systematic

Sampling: Z-axis measurements are measured at regularly spaced intervals. One example is a DEM

► Adaptive

Sampling: Z-axis measurements are made a selected points that are assumed to be

Figure 9.2

DEM or TIN? ► DEMs

and TINs can be converted to one another by well-established techniques.

► Which

to use?

 The nature of the terrain. TIN is better for complex terrains to capture local variations.  Purpose of modeling. DEMs are easier to process but less accurate.  The needs of specific applications; i.e., shaded relief maps work better with TINs  The method of data acquisition. TIN approach lends itself to field surveys while DEM to remote sensing.

Characteristics of a DEM ►

Linear array of sampled Z-axis points.

►

Spacing between profiles represents one dimension of the spatial resolution.

►

Three types of points in the grid:   

►

Regular Points First Points Corner Points

Coordinates only stored for the first points along a profile and the corner points

Figure 9.3

Characteristics of the TIN ► Terrain

is recorded as a continuous surface made up of a mosaic of nonoverlapping triangular facets formed by connecting selectively sampled elevation points using a consistent method of triangle construction.

Figure 9.6

Figure 9.7