Yes, that makes a lot of sense to me. Thanks a bunch to you both!

Thanks for the tip.

To elaborate on my problem: imagine you are standing on an ondulated landscape with a chalk spray in your hand. You want to draw lines where the flower beds will go, where the electicity cables will go, the water irrigation, the lawn etc. So you take your spray and walk up and down the terrain, marking each element.

Using your trick I could take a centered top view, take the freehand line tool, start with the highest point, keep it restricted to the horizontal axis (haven't figured that out yet) and start drawing the shape before I pull it out to become the intersection body.

Of course it would be much easier if I could just use the freehand line tool like the chalk spray, but restrict it to the surface of the terrain. Without pressing any additional keys the freeline tool does follow the terrain surface ... sometimes ... and for a while, only to wander off eventually, resulting in a hovering surface.

I experimented a bit more and found that if I start on the face of the terrain, press and hold the up arrow key to fix the freehand line tool to the "pink axis", and go really sloooowly, I'll get reasonably good results.

Any more reliable (and faster) approaches welcome!

Hello!
I would like to measure the area of a terrain subset I created with the sandbox tools.
First attempt: freehand tool -> gives me some surface and in the info box its size, but it is usually hovering over the actual terrain (or underneath) as it cannot follow the contours correctly
Second attempt: installed "Draw on Surface" plugin -> doesn't really work on terrains (or maybe I didn't figure out to parameterize the drawing tools)
Third attempt: Select the (sub-)mesh -> only gives me the surface if I were to remove all edges, but I didn't find a tool to do that
I am surprised I couldn't find anything on the internet as this should be a common task for landscape designers or gardeners (in my case).
Thanks for your help!