vtkLabelPlacementMapper with coincident points

raungst · February 20, 2026, 3:34pm

Hi,

I’m currently using vtkLabelPlacementMapper to label a bunch of points in my scene. My trouble is that if I label points that are coincident, vtkLabelPlacementMapper is moving the points so they don’t overlap anymore. I realize this is part of the purpose of this mapper, but is there anyway I can have it leave the points alone even if the labels end up not being readable because their on top of each other?

Thanks!
Robby

lassoan · February 21, 2026, 4:21pm

We ran into the same issue in 3D Slicer. My conclusion was that the implementation of vtkPointSetToLabelHierarchy/vtkLabelPlacementMapper is not just buggy but incomplete. Among other things, label position perturbation is not fully implemented and its current behavior is basically random.

There is no on/off switch for the label position perturbation (it is one of the many things that would need to be implemented), but we applied the following workaround: in vtkPointSetToLabelHierarchy set maximum depth to a large number (e.g., 10) and in vtkLabelPlacementMapper set PlaceAllLabelsOn:

github.com/Slicer/Slicer

Modules/Loadable/Markups/VTKWidgets/vtkSlicerMarkupsWidgetRepresentation2D.cxx

c792b1fb8


      
          // PointSetToLabelHierarchyFilter perturbs (slightly modifies) label positions around
          // coincident points, but the result is far from optimal (labels are quite far from
          // the control point and not at the same distance).
          // We set maximum depth from the default 5 to 10 to essentially eliminate
          // this coincident label position perturbation (perturbation may still be visible
          // when zooming into the view very much). Probably it would be cleaner to have on option
          // to disable this label position adjustment in PointSetToLabelHierarchyFilter.
          this->PointSetToLabelHierarchyFilter->SetMaximumDepth(10);
          
          this->LabelsMapper->PlaceAllLabelsOn();

There is an issue submitted for this in 2017:

https://gitlab.kitware.com/vtk/vtk/-/issues/17097

raungst · February 21, 2026, 5:00pm

Thank you! Setting the maximum depth to 10 looks like it fixed it for me.