Sectionplot: colorize the surface DEM-line based on a soil information layer

[HenrikSpa]

It would be nice to make the surface DEM-line to, instead of being a single color, be colorized using a layer with soil information.

Some loud thinking:

• Make a memory layer and copy the digitized DEM-line to it.
• Split the line into multiple lines using a polygon.
• Give each line a specific attribute from the polygon, (ex. a column with soil types like sand, gravel etc.)
• Instead of plotting the DEM-line, plot each splitted part. Now colorize them based on the specific attribute. Preferebly with colors that match bore hole soil types colors.

[HenrikSpa]

An early "test"-version of this is now working in qgis3-branch.

I haven't made any gui-changes for it yet (not sure where to put those settings).

The grading is done by plotting using fill_between using different alpha values (reducing alpha linearly currently). 10 plots works well while zoomed out, but it could be increased if needed to make the gradient finer.

The gradients currently extend 2 m below surface, but this could be adjusted also. Maybe % or y-axis or something.

Another example:

[HenrikSpa]

The plan is to make it generic so that any dem could be coloured by any polygon layer. (it uses geoshort and zz_stratigraphy_plots currently). The bedrock could be styled in a similar way.

[HenrikSpa]

It's in qgis3_secplot_dem_style, not in general qgis3-branch.

[HenrikSpa]

I've made a change to the way this works to better separate the bore hole stratigraphy from the surface layer stratigraphy. It now picks the color from the surface geology shapefile style instead of using the same colors and hatch as the bore hole stratigraphy.

Example of this: