[Paraview] Can you use bands in colour maps?

[David Thompson]

Hi Joe,

> By default, all the colour maps in ParaView are continuous between points.  I'd like to have only one colour in between points I set in the XML map, is this possible?

In the current release of ParaView, you can click on the "Edit color map" button in the toolbar and turn on "Use Discrete Colors" in the color editor. By changing the number of colors with the neighboring slider, uniform ranges of scalar values will be assigned a single color.

In an upcoming release, discrete color maps will be available. Discrete colormaps do not interpolate colors; instead they are looked up in a table, so a single large difference in values will not force any small variations to be lumped into a single color band. However, this requires your scalar field to take on a small number of distinct values (32 or fewer); colors are assigned to a single value, not a range.

To map non-uniform ranges of values to a single color each, you really should create a derived, integer-valued variable and use it for coloring -- regardless of whether you use continuous colormaps in the current release or plan to use categorical color maps later. The calculator filter's floor, ceil, and round functions might be worth a try in creating the derived field; if there's not a simple expression to convert each range of interest to an integer, the Python calculator will let you apply a tabular function.

Finally, it *may* also be possible to achieve what you desire with a custom XML color map by placing control points with different colors very close to each other to create a discontinuous color map. This would be difficult to adjust in the color editor should the control points need to be repositioned, but might be the easiest thing to do if the bands are fixed values or fixed fractions of the total range.

	David