# What does the parameter 'index' mean in GetScalarOpacity function? the volume, the point, the cell or others?

**URL:** https://discourse.vtk.org/t/what-does-the-parameter-index-mean-in-getscalaropacity-function-the-volume-the-point-the-cell-or-others/7633
**Category:** Support
**Created:** [January 13, 2022, 7:26am UTC](https://discourse.vtk.org/t/what-does-the-parameter-index-mean-in-getscalaropacity-function-the-volume-the-point-the-cell-or-others/7633 "2022-01-13T07:26:43Z")
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### Author: ![YuezhenQin](https://discourse.vtk.org/letter_avatar_proxy/v4/letter/y/f1d935/32.png) [@YuezhenQin](https://discourse.vtk.org/u/YuezhenQin)
#### Post date: [January 13, 2022, 7:26am UTC](https://discourse.vtk.org/t/what-does-the-parameter-index-mean-in-getscalaropacity-function-the-volume-the-point-the-cell-or-others/7633/1 "2022-01-13T07:26:43Z")

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In doc,  
[vtkPiecewiseFunction](https://vtk.org/doc/release/5.0/html/a01845.html)\* vtkVolumeProperty::GetScalarOpacity ( int _index_ )

Get the scalar opacity transfer function for the given component.

What does the component mean? How to use it? If there exist any example to use this function?