2-8 Data Structure for Continuous Surface Model

In GIS, continuous surface such as terrain surface, meteorolgical observation (rain fall, temperature, pressure etc.) population density and so on should be modeled. As sampling points are observed at discrete interval, a surface model to present the three dimensional shape ; z = f (x, y) should be built to allow the interpolation of value at arbitrary points of interest.

Usually the following four types of sampling point structure are modeled into DEM.

Grid at regular intervals :
Bi-linear surface with four points or bi-cubic surface with sixteen points is commonly used

Random points :
Triangulated irregular network (TIN) is commonly used. Interpolation by wieghted polynomails is also used.

Contour lines :
Interpolation based on proportional distance between adjacent conmtours is used. TIN is also used.

Profile :
Profiles are observed perpendicular to an alignment or a curve such as high ways. In case the alignment is a straight line, grid points will be interpolated. In case the alignment is a curve, TIN will be generated.

Figure 2.11 shows different types of DEMs.