17.30. Interpolation and contouring
Module contributed by Paolo Cavallini - Faunalia
Note
This chapter shows how to use different backends to calculate different interpolations.
17.30.1. Interpolation
The project shows a gradient in rainfall, from south to north.
Let’s use different methods for interpolation, all based on vector points.shp
, parameter RAIN
:
Warning
Set cell size to 500 for all analyses.
[Inverse distance to a power; Power: 4; Search radius: Global; Search range: all points]
[Power:4]
[Radius1&2: 50000]
Then measure variation among methods and correlate it with distance to points:
[Unselect Propagate NULLs, Aggregate operation: stddev]
onpoints.shp
- to show the correlation matrix; check the significance of the correlation e.g. with
Thus, areas far from points will have less accurate interpolation.
17.30.2. Contour
Various methods to draw contour lines [always step= 10] on the stddev raster:
[NB: in some older SAGA versions, output shp is not valid, known bug]