# How to correctly use the coincidenttopology related methods on a mapper ?

**URL:** https://discourse.vtk.org/t/how-to-correctly-use-the-coincidenttopology-related-methods-on-a-mapper/6888
**Category:** Web
**Created:** [October 14, 2021, 4:08pm UTC](https://discourse.vtk.org/t/how-to-correctly-use-the-coincidenttopology-related-methods-on-a-mapper/6888 "2021-10-14T16:08:09Z")
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### Author: ![andreasbuykx](https://discourse.vtk.org/user_avatar/discourse.vtk.org/andreasbuykx/32/8137_2.png) [@andreasbuykx](https://discourse.vtk.org/u/andreasbuykx)
#### Post date: [October 19, 2021, 8:49am UTC](https://discourse.vtk.org/t/how-to-correctly-use-the-coincidenttopology-related-methods-on-a-mapper/6888/3 "2021-10-19T08:49:30Z")

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I wrote a script to test/demonstrate our use of the coincident topology parameters, which may be of use to you.

Note that the coincident topology behavior changed since 8.1.1 (or maybe 8.2 I’m not sure).  
The factor is no longer used for polygons and lines. The 9.0 versions scale the net unit (the sum of common and relative unit values) for an actor by the actor’s length. This caused [problems](https://discourse.vtk.org/t/coincident-topology-offset-parameters/4836) for us which were the reason for me to develop this script. As of 9.1 this scaling by actor length has been reverted (thanks @sankhesh!).

[coincident-topology-demo.py](https://discourse.vtk.org/uploads/short-url/7iyBTEq4ueLkcfLcJ7mkG7zIc8c.py) (14.6 KB)

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