interpolationqgisvolume
Given data
From a shapefile with ca. 80 points (displaying borewells) I extracted two interpolations:
Desired outcome
I need to know the volume of the first geological layer in the area of interest.
I am a beginner and not familiar with GRASS. It would be great if you could explain everything step by step, maybe even providing some screenshots.
The usage of SAGA raster volume is slightly different from what you would expect with ArcGIS Cut/Fill, as it is a tool to calculate a volume above a reference surface.
How about simply using QGIS Raster Calculator?
(1) Subtract raster_b from raster_a
(2) You will obtain output raster.
(3) If it was ArcGIS Cut Fill tool, it will immediately give you Cut volume and Fill volume summarized in a table. With QGIS, you would probably use Raster layer statistics tool (in QGIS geoalgorithm | Raster tools) or other plugins, which fits for your target statistics.
Using IDW or TIN is the correct approach.
Make sure:
Pixel Size (or, conversely, number of Rows and Columns)Once you get the raster properly placed, you can tune parameters like Distance Coefficient P.
Best Answer
The first step is to define a grid resolution (g.region) and then convert your points to rasters with v.surf.idw. Check that the rasters look OK. Sometimes interpolating introduced artifacts. Then, subtract the lower from the upper layer to get thickness. This could be done with
r.mapcalc "thick = top - bot". Finally, the volume is the thickness times the x resolution times the y resolution.This answer doesn't explain everything nor use screenshots (I use the CLI not the GUI, so don't have any screenshots to provide), but it might help you get started. If you can use this to break down the problem to smaller tractable issues, you should be able to figure them out, or post more specific questions here that will be easier to answer.
Edit: I just realized that your title says
QGIS. I noticed thegrasstag and answered about how to do this in GRASS.