Aspect computation

Introduction

Slope aspect can be computed from the normalized gradients (see Slope computation page). It can be shown that for the slope aspect ψ we have:

%5Ctan%5Cpsi%3D%5Cfrac%7B%5Cdelta%20f%2F%5Cdelta%20x%7D%7B%5Cdelta%20f%2F%5Cdelta%20y%7D%2C
Equation 1

 

Readers are warned that this formula should not be carelessly replaced by using:

%5Cpsi%3D%5Carctan%5Cleft(%5Cfrac%7B%5Cdelta%20f%2F%5Cdelta%20x%7D%7B%5Cdelta%20f%2F%5Cdelta%0Ay%7D%5Cright)%2C
Equation 2

the reason being that the latter formula does not account for southeast and southwest quadrants, nor for cases where δf ∕ δy = 0. (In the first situation, one must add 180 to the computed angle to obtain an angle measured from North; in the latter situation, ψ equals either 90 or -90, depending on the sign of δf ∕ δx.)

Learning outcomes

  • 11 - Spatial analysis: classes of functions

    Classify and explain spatial analysis functions (measurements, classification, overlay, neighbourhood and connectivity) in a raster and vector environment (level 1 and 2).

Prior knowledge

Outgoing relations

Learning paths