Sampling points in raster without generating new file in QGIS

Question

I am aware that there are tools available in QGIS for sampling a raster at any given point from a shapefile.

The methods I've tried are:

• Point sampling tool plugin
• Raster analysis > sample raster values
• Saga > Raster Values to Points

They all generate an output file, which contains the points and the altitude as an attribute (I always sample from a DEM).

Now, my workflow involves the constant change of a point shapefile, and then getting the Z values (by sampling a DEM), so end up generating a lot of trash files. Further, this implies also that I have to keep changing the path in my code for the new updated point file with the new altitudes.

Is there a tool I could use to sample a raster by just updating an attribute in the attribute table of the point shapefile?

Answer 1

You can use the raster_value function in an expression in the Field Calculator to update a field in your point layer with the pixel value from an underlying raster:

raster_value( 'DEM', 1,  $geometry )

Where 'DEM' is the name of your raster layer, and 1 is the band number.

You could also use this expression in a virtual field so that the value will be updated on the fly if you add or edit point features.