17.30. Interpolation and contouring

Modulo contribuito da Paolo Cavallini - Faunalia

Nota

Questo capitolo mostra come utilizzare diversi backend per calcolare interpolazioni differenti.

17.30.1. Interpolazione

Il progetto mostra un gradiente di precipitazioni, da sud a nord. Usiamo diversi metodi di interpolazione, tutti basati sul vettore points.shp, parametro RAIN:

Avvertimento

Imposta la dimensione della cella a 500 per tutte le analisi.

• GRASS ► v.surf.rst

• SAGA ► Multilevel B-Spline Interpolation

• SAGA ► Inverse Distance Weighted [Inverse distance to a power; Power: 4; Search radius: Global; Search range: all points]

• GDAL ► Grid (Inverse Distance to a power) [Power:4]

• GDAL ► Grid (Moving average) [Radius1&2: 50000]

Then measure variation among methods and correlate it with distance to points:

• GRASS ► r.series [Unselect Propagate NULLs, Aggregate operation: stddev]

• GRASS ► v.to.rast.value on points.shp

• GDAL ► Proximity

• GRASS ► r.covar to show the correlation matrix; check the significance of the correlation e.g. with http://vassarstats.net/rsig.html.

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:

• GRASS ► r.contour.step

• GDAL ► Contour

• SAGA ► Contour lines from grid [NB: in some older SAGA versions, output shp is not valid, known bug]