# How to determine the first vertex of a regular polygon drawn with vtk.vtkRegularPolygonSource()?

**URL:** https://discourse.vtk.org/t/how-to-determine-the-first-vertex-of-a-regular-polygon-drawn-with-vtk-vtkregularpolygonsource/10691
**Category:** Development
**Tags:** python, code, proposal
**Created:** [February 15, 2023, 11:06am UTC](https://discourse.vtk.org/t/how-to-determine-the-first-vertex-of-a-regular-polygon-drawn-with-vtk-vtkregularpolygonsource/10691 "2023-02-15T11:06:35Z")
**Posts on this page:** 2
**Page:** 1

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### Author: ![jumbojing](https://discourse.vtk.org/user_avatar/discourse.vtk.org/jumbojing/32/5578_2.png) [@jumbojing](https://discourse.vtk.org/u/jumbojing)
#### Post date: [February 15, 2023, 11:06am UTC](https://discourse.vtk.org/t/how-to-determine-the-first-vertex-of-a-regular-polygon-drawn-with-vtk-vtkregularpolygonsource/10691/1 "2023-02-15T11:06:35Z")

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How to determine the first vertex of a regular polygon drawn with vtk.vtkRegularPolygonSource()?  
Or What is the projection direction of the coordinates of the first vertex of a regular polygon drawn with `vtk.vtkRegularPolygonSource()`? Is it unique?e.g. [1,0,0] or [-1, 0, 0]?  
@lassoan

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### Author: ![lassoan](https://discourse.vtk.org/user_avatar/discourse.vtk.org/lassoan/32/50_2.png) [@lassoan](https://discourse.vtk.org/u/lassoan)
#### Post date: [February 15, 2023, 12:40pm UTC](https://discourse.vtk.org/t/how-to-determine-the-first-vertex-of-a-regular-polygon-drawn-with-vtk-vtkregularpolygonsource/10691/2 "2023-02-15T12:40:35Z")

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Such low level details are probably not documented and subject to change, but you can see how this class works now by looking at its source code.