[GIS] Perpendicular lines on line using QGIS

Question

I am using QGIS. I want to create perpendicular Lines on another Line (River). The Lines should be created on points on the Line and should have a length of 40 Meters. I want to create the red lines in the picture below (for the complete River).

Answer 1

Edited answer: My first solution (see below) was for visualisation purposes only. But as you mentioned afterwards, you need the actual geometry. So this here is how to do it:

Go to Menu Processing / Toolbox / Create points along input lines to create points on the line in a set distance - as I can see in your screenshot, the points should have a distance of 100 meters along the line, so set the distance to 100. This creates a new pointslayer interpolated points with an attribute angle that you can use to create perpendicular lines.

As you need it as an actual geometry, use Menu Processing / Toolbox / Gemoetry by expression and set the layer interpolated points as input, geometry type as line and introduce the following expression

extend(
   make_line(
      $geometry,
       project (
          $geometry, 
          40, 
          radians("angle"-90))
        ),
   40,
   0
)

This will add an additional lines layer with the perpendicular lines:

This here is the first solution that does not create new geometries, but is good for visualisation purposes:

Add an additional symbol layer to your line and define it as simple marker, selecting the symbol and size as shown in the screenshot:

In this example, I have created a marker on every vertex. If you need a marker in a regular distance along the line, just make the settings accordingly as shown in the second screenshot (the settings in the red box; the arrow shows where to check for the first solution, every vertex):