QGIS – Variogram Model Using SAGA in Processing

krigingqgisqgis-processingsagavariogram

QGIS 2.14 (Win) comes with SAGA 2.12, which Ordinary Kriging supports 6 variogram model options.

SAGA 2.12

However, if I run SAGA Ordinary Kriging from QGIS Processing Toolbox, there is no drop down menu. Only an entry box in which an equation a + bx is shown.

QGIS Processing SAGA Ordinary Kriging

QGIS 2.14 user guide Kriging explains these options, so I can expect them coming. (future…not now).

Do you know any documentation about how to set variogram models in SAGA on QGIS Processing Toolbox? (Ideally, is there any working example?)

At the moment I am playing with Meuse river dataset, so a reference to Spherical model is desirable. (It is not important for now, though.)

enter image description here

So far I tried to manually put equation in the box (like above), which gave me a Kriging-like map. But I have zero confidence in what I am doing.

I installed SAGA 3.0 on QGIS 2.18 Processing, which was the same.

Best Answer

Finally, I found this template in SAGA GUI (2.0.1), in the interactive mode of Ordinary Kriging (global).

equation template

So a Spherical model can be like: new semivariogram model

And I got this; result

[Note] If anybody kindly volunteer to test this workflow, this sample point data and parameters are reproduced by R commands:

library(sp)
data(meuse, package= "sp")
coordinates(meuse)= ~x + y
proj4string(meuse) <- CRS("+init=epsg:28992")

library(rgdal)
writeOGR(meuse, ".", "meuse_points", driver = "ESRI Shapefile")

library(gstat)
vgm1 <- variogram(log(zinc)~1, meuse)
fit.variogram(vgm1, vgm("Sph"))       # Nugget= 0.214, Range= 514.4
plot(vgm1)                            # Sill ~ 0.85 by visual
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