I'm trying to generate contour lines/isolines from groundwater points (groundwater depth) with SAGA (I tried before with QGIS, contour plugin, but the result was not good looking, too angular lines).
I have uploaded my groundwater points into SAGA, but I can't find the right tool or the steps to draw the contour lines. Can somebody tell me the steps to do it?
Do I need to generate a grid first ?
Yes you need to create the grid first and then create contour lines from the grid.
SAGA GIS has many tools to interpolate from points, which you can find them from Geoprocessing -> Grid -> Gridding -> Interpolation from Points, as you can see below:
You need to test several tools and choose the one that fits your needs.
Then from Geoprocessing -> Shapes -> Grid -> Vectorization -> Contour Lines from Grid, you can extract the contour lines from the interpolated grid you did in the previous step.
From version 2.1.3 SAGA contains a toolchain which will do exactly this. It is called "contour lines from points".
Note that this toolchain actually interpolates the data to a grid first and then creates contour lines. This may not give you all the flexibility you want, and running both tools independently may be a better option.
If your lines are too angular, make sure you make the grid sufficiently small, and increase the "SCALE" option when creating the contour lines: http://www.saga-gis.org/saga_tool_doc/5.0.0/shapes_grid_5.html
To interpolate, the toolchain uses this tool: http://www.saga-gis.org/saga_tool_doc/5.0.0/grid_spline_4.html
