I would recommend using readily available VTK filters for point sampling, such as vtkPoissonDiskSampler and vtkPolyDataPointSampler. They produce approximately uniform grid even if the surface is uneven.
Full example:
modelNode = getNode('model')
# Sample points on the surface
sampler = vtk.vtkPoissonDiskSampler()
sampler.SetInputConnection(modelNode.GetPolyDataConnection())
sampler.SetRadius(10.0)
sampler.Update()
sampler.GetOutput().GetNumberOfPoints()
# Get point coordinates as numpy array
import vtk.util.numpy_support
pointData = sampler.GetOutput().GetPoints().GetData()
coordsArray = vtk.util.numpy_support.vtk_to_numpy(pointData)
# Create a markup point list
markupPointList = slicer.mrmlScene.AddNewNodeByClass('vtkMRMLMarkupsFiducialNode')
markupPointList.CreateDefaultDisplayNodes()
displayNode = markupPointList.GetDisplayNode()
displayNode.SetPointLabelsVisibility(False)
markupPointList.SetLocked(True)
# Set sampled point coordinates into the markup point list
updateMarkupsControlPointsFromArray(markupPointList, coordsArray)
Note that in the very latest Slicer Preview Release (that you download on 2022-09-03 or later) I’ve made some performance improvements in updateMarkupsControlPointsFromArray completes immediately instead in tens of seconds (if you have many points).
If you want to place points only in a specific part of the surface then you can clip the model using Dynamic Modeler module (Curve cut, Boundary cut, or Select by points tool) before you project.
You may also find this discussion useful: How to project points to Polydata? - #6 by will.schroeder - Support - VTK