# modify position of points on boundary of polydata surface

**URL:** https://discourse.vtk.org/t/modify-position-of-points-on-boundary-of-polydata-surface/5716
**Category:** Support
**Created:** [May 6, 2021, 4:13pm UTC](https://discourse.vtk.org/t/modify-position-of-points-on-boundary-of-polydata-surface/5716 "2021-05-06T16:13:04Z")
**Posts on this page:** 1
**Showing post:** 2

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### Author: ![bistek](https://discourse.vtk.org/user_avatar/discourse.vtk.org/bistek/32/2344_2.png) [@bistek](https://discourse.vtk.org/u/bistek)
#### Post date: [May 7, 2021, 4:40pm UTC](https://discourse.vtk.org/t/modify-position-of-points-on-boundary-of-polydata-surface/5716/2 "2021-05-07T16:40:33Z")

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Hello again! I have found some possible solutions.

(1) It looks like that using the function described in [topic 2530](https://discourse.vtk.org/t/how-to-extract-the-ids-of-the-boundary-points-of-a-surface/2530/2) it would be possible to extract an array of all the ids of the boundary nodes. In this case, I am still looking for a method to get the cell (triangles) ids and the edge ids (boundary edge of these triangles).

(2) Using [vtkGeometryFilter()](https://vtk.org/doc/nightly/html/classvtkGeometryFilter.html) with options PassThroughCellIdsOn() and PassThroughPointIdsOn() might do the trick. However I am still looking for examples on how to use this to select boundary edges (topological dimension 1) of a triangulated surface (made of triangle cells). Actually, it is not clear to me what the input and output of vtkGeometryFilter() is, and what options I have to get what I need: points, edges and triangles along the boundary of a surface, all correlated (e.g. triangle A has boundary edge B with nodes C and D).

Thanks!

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