[vtkusers] A bug in Above/BelowRangeColor mapping?

[marcin.krotkiewski]

Thanks, Mathieu,

I can do that. I might not have been very clear in the first paragraph, 
but the unexpected behavior comes from VTK. Paraview was mentioned here 
only as a simple way to reproduce the problem, and as an example. I'd 
like to avoid bothering too many people at once, but if you still think 
I should re-post, I can do that.

Thanks,

Marcin


On 10/15/2018 10:21 AM, Mathieu Westphal wrote:
> Hi Marcin,
>
> Regarding ParaView, you may want to post on our discourse instead
> https://discourse.paraview.org/
>
>
> Mathieu Westphal
>
>
> On Mon, Oct 15, 2018 at 9:38 AM marcin.krotkiewski 
> <marcin.krotkiewski at gmail.com <mailto:marcin.krotkiewski at gmail.com>> 
> wrote:
>
>     Hi,
>
>     I think the behavior of UseBelowRangeColor in both VTK 8.1.1, and
>     Parview 5.5 is wrong. As an example, I load a surface into Paraview,
>     rescale the color range to point data (elevation in this case, fig.
>     paraview.png), and enable the 'Use Below Range Color' checkbox.
>     What you
>     see is that part of the surface are colored with black (fig.
>     paraview_wrong.png), although they are in fact within the
>     automatically
>     computed value range. So they should get the usual color from the
>     lookup
>     table.
>
>     I also observe wrong behavior when I color the surface by a constant
>     value. In VTK, I set lower/upper bound on data values in
>     vtkLookupTable
>     to be the same. Say, my point data has value 50. I set the lookup
>     table
>     range to [60,60] and turn on Above/Below range color. Figure
>     constant_wrong.png shows that my surface is colored with the in-range
>     color, although it is below range. To get a correct coloring I
>     need to
>     spread the range a little bit, e.g., [60,61] (constant_below.png), or
>     [40, 41] (constant_above.png). But even in this case we go back to
>     the
>     first problem: for point values that are on the edge of the range VTK
>     uses out-of-range color (range [50,51], constant_extreme.png).
>
>     So the question is - is this behavior intended, and if so - how
>     should I
>     organize my color mapping and data ranges to get the expected
>     behavior?
>
>     Regards,
>
>     Marcin Krotkiewski
>
>
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