Re: a couple of questions about ColorControl setFunction method

• To: Bill Hibbard <hibbard@xxxxxxxxxxxxxxxxx>
• Subject: Re: a couple of questions about ColorControl setFunction method
• From: Donna L Gresh <gresh@xxxxxxxxxx>
• Date: Mon, 3 Feb 2003 12:33:28 -0500

Bill,
That all worked great; thanks!

Donna L. Gresh, Ph.D.
IBM T.J. Watson Research Center
(914) 945-2472
http://www.research.ibm.com/people/g/donnagresh
gresh@xxxxxxxxxx




                                                                                
                                                       
                      Bill Hibbard                                              
                                                       
                      <hibbard@facstaff.w        To:       Donna L 
Gresh/Watson/IBM@IBMUS                                              
                      isc.edu>                   cc:       visad 
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                      Sent by:                   Subject:  Re: a couple of 
questions about ColorControl setFunction method             
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                      02/03/2003 10:20 AM                                       
                                                       
                                                                                
                                                       




Hi Donna,

> I'm using the setFunction method of ColorControl to set a custom color
map.
> This mostly works, but I have a couple of questions. One is, is there a
> simple way to "unset" the function (that is, to have it go back to the
> default colormap)?  I tried naively setting the function to null but that
> did not work.  I want to allow the user to choose between several
> colormaps, including the default. I know I can build a custom map that
> looks like the default, but wanted to avoid that.

You can call:

  float[][] table
    BaseColorControl.initTableVis5D(new float[3][tableLength]);
  color_control.setTable(table);

to create the default color table of whatever length you like.
The call to setTable() will disable any Function passed to
setFunction().

> Second, I use a FlatField to represent the colormap, which gets passed to
> the setFunction method, with it constructed like this:
>
>       RealType cp = RealType.getRealType("cp");
>       RealType cr = RealType.getRealType("cr");
>       RealType cg = RealType.getRealType("cg");
>       RealType cb = RealType.getRealType("cb");
>       try {
>         RealTupleType crgb = new RealTupleType(cr, cg, cb);
>         FunctionType colormapfunction = new FunctionType(cp, crgb);
>         float[][] cpos = new float[1][pos.size()];
>         for (int i=0; i<pos.size(); i++) {
>           cpos[0][i] = pos.get(i);
>         }
>
>         Irregular1DSet colorbarpos = new Irregular1DSet(cp, cpos);
>
>         FlatField mycolormap = new FlatField(colormapfunction,
> colorbarpos);
>         double[][] samples = new double[3][colors.size()];
>         ColorRGBValue col;
>         for (int i=0; i<colors.size(); i++) {
>            col = colors.get(i);
>            samples[0][i] = col.r;
>            samples[1][i] = col.g;
>            samples[2][i] = col.b;
>         }
>
>       mycolormap.setSamples(samples);
>
> "pos" and "colors" are simply Java Vectors holding the 1D positons of the
> colormap or the 3D rgb colors of the map.  It seems that this creates a
> segmented colormap, in that there are abrupt boundaries between the
colors,
> instead of smooth. Is this how it works? i.e. do I have to have lots of
> points in my colormap to get a smooth appearance?

ColorControl samples Function values using
NEAREST_NEIGHBOR. Since this is essentially what
it does for a table, it seems to me that Function
should provide an alternative. So I changed it to
WEIGHTED_AVERAGE. Until the next VisAD release you
can find it at:

  ftp://ftp.ssec.wisc.edu/pub/visad-2.0/untested/BaseColorControl.java

Please let us know if this does not solve you
problem.

Cheers,
Bill

• References:
  • Re: a couple of questions about ColorControl setFunction method
    • From: Bill Hibbard