# Find the triangle on a sphere
**URL:** https://discourse.vtk.org/t/find-the-triangle-on-a-sphere/1655
**Category:** Support
**Created:** [August 26, 2019, 11:57pm UTC](https://discourse.vtk.org/t/find-the-triangle-on-a-sphere/1655 "2019-08-26T23:57:06Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@Elvis723](https://discourse.vtk.org/u/Elvis723)
#### Post date: [August 26, 2019, 11:57pm UTC](https://discourse.vtk.org/t/find-the-triangle-on-a-sphere/1655/1 "2019-08-26T23:57:06Z")
Hi! I want to find the triangle that contains a certain point on a sphere in vtk. How should I do that? I knew that spheres in vtk are by default approximated by triangles. Thanks in advance!
---
### Author:  [@Sebastien\_Jourdain](https://discourse.vtk.org/u/Sebastien_Jourdain)
#### Post date: [August 27, 2019, 3:41pm UTC](https://discourse.vtk.org/t/find-the-triangle-on-a-sphere/1655/2 "2019-08-27T15:41:34Z")
Is the question related to vtk.js or ParaViewWeb as you are posting in the Web topic?
Also what do you mean by “you want to find a triangle that is based on a point”. Are you thinking of picking? If not, you can iterate over the cells and if you find a cell that use the index of the point you care about, you would have the answer to your question.
---
### Author:  [@Elvis723](https://discourse.vtk.org/u/Elvis723)
#### Post date: [August 27, 2019, 8:48pm UTC](https://discourse.vtk.org/t/find-the-triangle-on-a-sphere/1655/3 "2019-08-27T20:48:50Z")
Sorry I am new here and am not familiar with the Web topic. So yes I am coding in Paraview. I want to calculate the location of a particle inside a cell after bouncing to the inner surface of the cell. I heard that “triangles” are used to approximate the surface of the cell, so I am thinking about finding that specific triangle the particle collides.
---
### Author:  [@Sebastien\_Jourdain](https://discourse.vtk.org/u/Sebastien_Jourdain)
#### Post date: [August 27, 2019, 10:47pm UTC](https://discourse.vtk.org/t/find-the-triangle-on-a-sphere/1655/4 "2019-08-27T22:47:03Z")
@cory.quammen how do we move topic?
---
### Author:  [@cory.quammen](https://discourse.vtk.org/u/cory.quammen)
#### Post date: [August 28, 2019, 3:21am UTC](https://discourse.vtk.org/t/find-the-triangle-on-a-sphere/1655/5 "2019-08-28T03:21:19Z")
Moderators can edit the original post and change the category. I have done so.