Terrain Analysis: Methods for Calculating Slope & Aspect: Ritter՚s, Horn՚s, & Computing Algorithms (Especially for GATE-Geospatial 2022)

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Two Types of Approximation Methods

Ritter՚s Algorithm

Use moving windows. The slope of the center cell can be estimated by the four immediate members.

Ritter՚s Algorithm

S is slope gradient if multiply S by 100, the unit is in percent slope. D is measured in radian with respect to x-axis, can be converted into degree from a north base of using algorithm.

Illustration 2 for Ritters_Algorithm
Illustration 3 for Ritters_Algorithm

Horn՚s Algorithm

Used in Arc/Info and ArcView. Use 8 neighboring cells and applies weight of 1 to 4 corner cells.

Horn՚s Algorithm for Slope and Aspect

Used in Arc/Info and ArcView. Use 8 neighboring cells and applies weight of 1 to 4 corner cells.

Computing Algorithms Using TIN

Illustration 4 for Computing_Algorithms_Using_TIN

Use bi-directional normal vector (vector perpendicular to the triangular surface) . Suppose a triangle is made of the three nodes:

Slope and Aspect of Triangle in TIN

The normal vectors are:

  • AB,
  • AC,

The three components of the normal vector are:

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