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

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## Ritter՚s Algorithm

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

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.

## Horn՚s Algorithm

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

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

## Computing Algorithms Using TIN

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

The normal vectors are:

- AB,
- AC,

The three components of the normal vector are: