Re: octaviz and color

[Jonathan Stickel]

I would have responded sooner, but I have been away at a conference ...

Jeff Abrahamson wrote:
> I've been playing with octaviz all morning.  It's very nice.  My need
> is to image surfaces for which I have triangular meshes, so I find
> myself using vtk_trisurf mostly.
>
> Near as I can tell, though, vtk_trisurf.m ignores anything I say about
> color.  Am I confused?

There are currently two ways to give color information to vtk_surf and 
vtk_trisurf: either a set of scalars corresponding to the individual 
points, or an [R,G,B] vector defining a single color for the entire 
plot.  For the former, the scalars are mapped through a color scheme to 
produce the final color of the surface.  In Octaviz CVS there is now a 
function to change the color mapping (vtk_colormap).

> What I want to be able to do is color certain triangles special
> colors, such as have a triangulated shape that is all light gray but a
> few regions I'll want to highlight in blue and a few others I'll want
> to highlight in red.
>
> As a toy example, suppose I want to discover regions of high
> curvature.  I'd then want to highlight triangles adjacent to high
> curvature areas so I can see how well my curvature program works.

Assigning scalar inputs and a color scheme may be sufficient for you. 
Assign high scalar values to points of high curvature and low scalar 
values elsewhere.  Then choose a color scheme that you like (from 
octave-forge functions).  You could also define your own colormap.

It is possible to use low level vtk programming to assign individual 
points (or triangles) certain colors, but for that you will need to 
learn VTK.  I think you will get what you want quicker by using the 
available scripts.

Jonathan



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