# Prevent reindexing between timesteps when using the ExtractSurface filter

**URL:** https://discourse.paraview.org/t/prevent-reindexing-between-timesteps-when-using-the-extractsurface-filter/16972
**Category:** ParaView Support
**Created:** [July 17, 2025, 11:25am UTC](https://discourse.paraview.org/t/prevent-reindexing-between-timesteps-when-using-the-extractsurface-filter/16972 "2025-07-17T11:25:50Z")
**Posts on this page:** 1
**Page:** 1

<div class="post-metadata">

### Author: ![SchnFlo](https://discourse.paraview.org/letter_avatar_proxy/v4/letter/s/48db29/32.png) [@SchnFlo](https://discourse.paraview.org/u/SchnFlo)
#### Post date: [July 17, 2025, 11:25am UTC](https://discourse.paraview.org/t/prevent-reindexing-between-timesteps-when-using-the-extractsurface-filter/16972/1 "2025-07-17T11:25:50Z")

</div>

Hello Support!

I am currently trying to compute a surface integral in paraview.

This is my current setup:

```
Source: .vtu
ExtractSelection: Extract cells around the surface of interest
ExtractSurface: Extract surfaces to make them selectable
ExtractSelection: To obtain only the surface I am interested in
IntegrateVariables: To compute a surface integral

```

Now, whenever I move to a new time step, the selected surface elements are assigned new IDs and thus have new orientation and values.

Is this expected behavior?  
What is the intended way to compute a surface integral?

I would be happy for any help on this!