Hi @AleksandarSM,
When adding objects to a HiddenLineDrawingParameters object, do so like this:
hld_params.AddGeometry(obj.Geometry, Transform.Identity, obj.Id);
where obj.Id is the id of the RhinoObject.
After computing the soluation, iterate through the HiddenLineDrawing.Segments collection to process each HiddenLineDrawingSegment object. A HiddenLineDrawingSegment should have a “parent curve”, or HiddenLineDrawingObjectCurve. This object will a source object, or HiddenLineDrawingObject. On this object you will find the id “tag” you added above.
– Dale