macfrog,

If I understand you correctly, you want a texture that follows the curve of a round wall. Well, there's no way to do that in SH3D. The only way I can think of, is to prepare a special texture and apply that.

If it is just a line that you want, you could make a wall of 0.1 cm high, give it the correct width and colour, and then use CopyAsNewFurniture to insert it.

Hans