QGIS - Find point position on line (lengthwise)

Question

I have a line layer with some lines, and a point layer whose points are located on those lines.

Now I need to get the position "along" the line where each point is (as in distance from start of the line along the line)

• A point located at the start of the line would be at 0 meters from start
• A point at the end of the line would be at <length> meters from start
• A point anywhere in between would be calculated accordingly

I found two answers that can surely help me achieve this, but they're using Python, and I'm almost sure there is a very simple button or processing tool that would do this instead.

• Length of line on specific point (from point layer)
• How do you measure distance from a line end point to a point on a separate layer in QGIS 3?

Answer 1

You can use the field calculator on the POINT_Layer. I don't think there is a one-click tool.

line_locate_point(aggregate('YOUR_LINE_LAYER_NAME','collect',$geometry),$geometry)

EDIT - Based on comment by she_weeds

The difference between the two methodes aggregate/collect and overlay_nearest can be seen if you have two lines in the line layer.

aggregate/collect count the distance along both lines and overlay_nearest starts with 0 at the beginning of each line.

line_locate_point(overlay_nearest('YOUR_LINE_LAYER_NAME',$geometry)[0], $geometry)