# Draw polygon and highlight points inside the polygon
**URL:** https://discourse.vtk.org/t/draw-polygon-and-highlight-points-inside-the-polygon/8682
**Category:** Support
**Created:** [June 8, 2022, 3:27pm UTC](https://discourse.vtk.org/t/draw-polygon-and-highlight-points-inside-the-polygon/8682 "2022-06-08T15:27:55Z")
**Posts on this page:** 9
**Page:** 1
### Author:  [@mdc93](https://discourse.vtk.org/u/mdc93)
#### Post date: [June 8, 2022, 3:27pm UTC](https://discourse.vtk.org/t/draw-polygon-and-highlight-points-inside-the-polygon/8682/1 "2022-06-08T15:27:55Z")
Hello everybody,
I would like to have some suggestions on how to implement the following:
I have a STL file and I would like to allow the user to draw a closed polygon and pick points of the mesh inside the closed contour.
How have I to approach the problem? I couldn’t find any example online.
Best
---
### Author:  [@mau\_igna\_06](https://discourse.vtk.org/u/mau_igna_06)
#### Post date: [June 8, 2022, 6:25pm UTC](https://discourse.vtk.org/t/draw-polygon-and-highlight-points-inside-the-polygon/8682/2 "2022-06-08T18:25:02Z")
I think it is doable on 2d and 3d (like blender) but you’ll need to put some work into it. Maybe check the contourFilter class
---
### Author:  [@Dave\_DeMarle](https://discourse.vtk.org/u/Dave_DeMarle)
#### Post date: [June 8, 2022, 9:49pm UTC](https://discourse.vtk.org/t/draw-polygon-and-highlight-points-inside-the-polygon/8682/3 "2022-06-08T21:49:32Z")
I would go with selection.
For a quick preview open up a .stl file in ParaView and click either of these buttons at the top of the RenderView window, then mouse drag in the view.
VTK’s selection is the basis for that. You should be able to find examples and tests in the VTK books and online sources.
---
### Author:  [@mdc93](https://discourse.vtk.org/u/mdc93)
#### Post date: [June 9, 2022, 9:25am UTC](https://discourse.vtk.org/t/draw-polygon-and-highlight-points-inside-the-polygon/8682/4 "2022-06-09T09:25:36Z")
Thanks for the reply,
what do you mean for “selection”?
---
### Author:  [@Dave\_DeMarle](https://discourse.vtk.org/u/Dave_DeMarle)
#### Post date: [June 9, 2022, 1:03pm UTC](https://discourse.vtk.org/t/draw-polygon-and-highlight-points-inside-the-polygon/8682/5 "2022-06-09T13:03:16Z")
See tests/examples and the book that involve vtkHardwareSelector, for example:
[Rendering/Core/Testing/Cxx/TestPolygonSelection.cxx · master · VTK / VTK · GitLab (kitware.com)](https://gitlab.kitware.com/vtk/vtk/-/blob/master/Rendering/Core/Testing/Cxx/TestPolygonSelection.cxx#L122)
---
### Author:  [@mdc93](https://discourse.vtk.org/u/mdc93)
#### Post date: [June 10, 2022, 7:21am UTC](https://discourse.vtk.org/t/draw-polygon-and-highlight-points-inside-the-polygon/8682/6 "2022-06-10T07:21:13Z")
Thanks for the reply. I forgot to add that I would like to achieve this using Python.
Is there any example involving python?
---
### Author:  [@Dave\_DeMarle](https://discourse.vtk.org/u/Dave_DeMarle)
#### Post date: [June 10, 2022, 1:28pm UTC](https://discourse.vtk.org/t/draw-polygon-and-highlight-points-inside-the-polygon/8682/7 "2022-06-10T13:28:24Z")
I do not know.
---
### Author:  [@mdc93](https://discourse.vtk.org/u/mdc93)
#### Post date: [June 27, 2022, 8:45am UTC](https://discourse.vtk.org/t/draw-polygon-and-highlight-points-inside-the-polygon/8682/8 "2022-06-27T08:45:08Z")
As suggested, I looked at HardwareSelector example. In the example linked ( **TestPolygonSelection.cxx** ) the draw-polygon interactor style is involved. As concerns the Python wrapper the method “GetPolygonPoints” has not been implemented because it returns a vtkVector2i, which is difficult to wrap. So I found this re-write of the vtk class on github [HERE](https://gist.github.com/mhogg/4863cf0b91e2f85a56d52b8a6981e325). Just to test the class I wrote this piece of code:
>
```
def loadSTL(filenameSTL):
readerSTL = vtk.vtkSTLReader()
readerSTL.SetFileName(filenameSTL)
# 'update' the reader i.e. read the .stl file
readerSTL.Update()
polydata = readerSTL.GetOutput()
print ("Number of Cells:", polydata.GetNumberOfCells())
print ("Number of Points:", polydata.GetNumberOfPoints())
# If there are no points in 'vtkPolyData' something went wrong
if polydata.GetNumberOfPoints() == 0:
raise ValueError("No point data could be loaded from " + filenameSTL)
return None
return polydata
colors = vtk.vtkNamedColors()
mesh_path = path of the STL file
mesh = loadSTL(mesh_path)
mapper = vtk.vtkPolyDataMapper()
mapper.SetInputData(mesh) # maps polygonal data to graphics primitives
actor = vtk.vtkActor()
actor.SetMapper(mapper)
actor.GetProperty().EdgeVisibilityOn()
actor.GetProperty().SetLineWidth(0.3)
ren1 = vtk.vtkRenderer()
ren1.AddActor(actor)
ren1.SetBackground(colors.GetColor3d('Navy'))
renWin = vtk.vtkRenderWindow()
renWin.AddRenderer(ren1)
renWin.SetSize(600, 600)
renWin.SetWindowName('HardwareSelector')
iren = vtk.vtkRenderWindowInteractor()
iren.SetRenderWindow(renWin)
#interactor style-->draw polygon
polystyle = InteractorStyleDrawPolygon()
polystyle.SetDefaultRenderer(ren1)
iren.SetInteractorStyle(polystyle)
iren.Initialize()
iren.Start()
```
The STL file is loaded correctly but the interactor seems not working because anything happens when I clicked the mouse left button. I added–\> print (“pressed”) inside the callback OnLeftButtonUp and it is executed so that it seems that self.interactor is None. How can I fix it?
---
### Author:  [@mdc93](https://discourse.vtk.org/u/mdc93)
#### Post date: [June 28, 2022, 1:09pm UTC](https://discourse.vtk.org/t/draw-polygon-and-highlight-points-inside-the-polygon/8682/9 "2022-06-28T13:09:34Z")
Could anyone help me?