[Paraview] colormap nan opacity

[David Thompson]

Hi Ryan,

> I use paraview to render ocean model data. My datasets are usually rectilinear grids ...
> ... The colormap editor allows you to choose your NaN color, but this dialog doesn't include an alpha / opacity option. ...
> Instead, what I have to do is use a clip filter to mask the NaNs, which ends up turning my rectilinear grid data into unstructure grid data, ...

I haven't worked with rectilinear grids in a while... but at least one structured-data PV representation accepts a blanking array. Would it be possible to use that to cull cells instead of the NaN color?

	David