Calculate the angle between line segments in a multilinestring or linestring in QGIS

Question

I need to calculate the angle between line segments in a long chain of linestring as in the figure below:

The way I approached this is:

1. I assigned the id to the feature using:$id

2. Now each feature is assigned a unique id, I calculated the azimuth of each line segment using:

CASE
   WHEN ((yat(-1)-yat(0)) = 0 and (xat(-1) - xat(0)) >0) THEN 90
   WHEN ((yat(-1)-yat(0)) = 0 and (xat(-1) - xat(0)) <0) THEN 270
   ELSE (atan((xat(-1)-xat(0))/(yat(-1)-yat(0)))) * 180/pi() + 
       (180 * (((yat(-1)-yat(0)) < 0) + (((xat(-1)-xat(0)) < 0 AND (yat(-1) - yat(0)) > 0)*2)))
END

3. Then, I calculated the angle difference between the consecutive if as:

attributes(
    get_feature_by_id(
        @layer ,
        $id + 1
        )
    )['Azimuth'] - "Azimuth"

The main issue with my approach is the id might not always be assigned to the consecutive line segment. So there could be a simpler way to find the angle between the line segments in a long chain of linestring.

Answer 1

A simpler method might be using "Vector Geometry>Points along geometry", ~if~ the line segments are all same length, set this length to "Distance". Use offset 0 and end offset 0. The output will be points with distance along line, and angle between subsequent points. Can't tell from diagram if segment length max-min == 0 -edit- and even if the line segments are not the same length, set distance low e.g. 1m, and with a chain of points each with an angle to subsequent point, filter the output to remove redundant data.