Extract raster value at each vertex from line, while keeping the line

Question

So I have a line that is basically drawn from two points. A starting point and an end point. It looks like this:

I then densify the line by count and set the value to e.g. 50

Then I explode the line so that I get one feature (row) per vertex (I am not sure if that step is a good idea)

And then I do not know how to continue. My first Idea was to use the profiles from lines tool from SAGA. It does work and creates a point for each cell (actually the densifying might be unnecessary too) which holds the raster value. I also added the field rn for the row number.

However, when I then run the points to path tool, the height information gets lost.

Another idea was to simply use the sample raster tool for the exploded line. However, I cannot use the line as vector layer input for sampling the raster values.

Anybody has an idea on how I can output a line that for each vertex has the height information from the raster?

Answer 1

You can use "Drape (set Z value from raster)" tool to set the z value of every vertex in the densified line to a value sampled from a raster.

Answer 2

Using QGIS expressions, use this expression:

raster_value( 'DEM', 1, start_point($geometry))

This is to get the elevation from the raster called DEM, raster band 1 for the line's start point. To get the elevation of the line's end point, simply change start_point to end_point.

---

Variant:

If you want to calculate the elevation along a line with just two vertices at a regular interval, you can use the following expression that generates an array of elevation values - for each point on the line in a regular interval - an interval that can be defined on line 3 (here: 100):

array_foreach(
    generate_series(
        0, length($geometry), 100  -- change interval here
    ),
    raster_value (
        'DEM',
        1,
        line_interpolate_point( 
            $geometry,
            @element
        )
    )
)