[abenedik]

I was able to reproduce the problem and can confirm that this is a bug in LineSelectorData - it does not work with MultiPolyLineVisual3D.

This has been fixed in the development version and will be available in the next version of Ab3d.PowerToys (v8.2 - cannot say when this will be released; not very soon). If you want the fixed code before the next release please send me a request by email or private message and I will send you the fixed source for LineSelectorData.


You can also use a simple workaround:
Instead of creating an instance of LineSelectorData with passing MultiPolyLineVisual3D as a parameter, you can use the constructor that takes Point3DCollection or List<Point3D>:

Code:

//var lineSelectorData = new LineSelectorData(multiPolyLineVisual3D);
var lineSelectorData = new LineSelectorData(multiPolyLineVisual3D.PositionsList[0], isLineStrip: true);

Note that in this case you will not be able to use the LineVisual3D property in LineSelectorData when checking which line is the closest.