MODÉLISER TERRAIN SURFER 12 SOFTWARE

MODÉLISER TERRAIN SURFER 12 SOFTWARE

In almost all instances software packages apply grid-based computation, with TINs being first converted to grid format. Hence slope calculations will use approximations to the formula above depending on the surface model used, which is itself an approximate representation of the true surface. However, surfaces within GIS are rarely if ever represented by analytic functions - typically they will be modeled as TINs or grids, with a finite resolution. It is closely related to the formula for Euclidean distance, and simply shows how much the surface F rises with a small fixed increment in x and y. This formula is not based on a rise-over-run calculation over a fixed interval, but rather assumes that a plane surface can be placed at any point on the surface F( x,y) in such a way that it only just touches the surface - it is a tangential plane and relies on the notion of infinitesimally small distances. S t=degrees(tan ‑1( S))= 360tan ‑1( S)/2 πįor an analytical surface, F( x,y), slope is defined as the magnitude of the first derivative of the surface function: To convert between the two one would use an expression such as: The normal use of the term slope within GIS packages is the tan() value S t, usually reported in degrees from the horizontal (11.3deg in this example). For gentle slopes (less than 1:4) this ambiguity in the definition of slope is not serious, but in general the tan() version is preferred. If the run were taken as the surface distance rather than the plane distance then we would have S=sin( S t). This ratio is actually the tangent function: S=tan( S t) where S t is the terrain slope in radians. If this was 2 meters, for example, the rise over run would be S=2:10 or 1:5 or 0.2 or 20%. In practice we would specify some distance over which the slope is to be calculated, such as the amount of rise over a 10 meter distance in the plane. the steepest path up or down the surface. change in elevation) over run in some direction, usually the direction for which the rise over run is greatest, i.e. The common notion of the slope of a surface or terrain, t, is the amount of rise (e.g. Slope is one of the most widely used of surface attributes so understanding how it is generated and what alternatives exist is extremely important. The magnitude or size of the gradient is the slope, whilst the direction in which the maximum value of this magnitude occurs is known as the aspect. an object that has both magnitude and direction. The term gradient refers to a vector quantity, i.e.

Modéliser terrain surfer 12