Re: Specific alpha values

• To: Andrew Donaldson <A.Donaldson@xxxxxxxxxx>
• Subject: Re: Specific alpha values
• From: Bill Hibbard <hibbard@xxxxxxxxxxxxxxxxx>
• Date: Tue, 22 May 2001 05:11:07 -0500

Hi Andrew,

>   I've got some radar data in my visad display, which I am overlaying
> over a filled in map and some other stuff.  The radar data is from
> a McIDAS ADDE image server.
> 
>   The bad bit is that a large black box surrounds the small amounts
> of rain (radar data).
>   So what I want to do is set 0 values in the radar data to be
> transparent.
>   This is something along the lines of mapping radarValue to ALPHA,
> but not quite, as I don't want a linear relationship.. I want to
> define my own function (in loose language).  This seems to be
> possible with mapping samples to colours, where you get your mouse
> and choose the R, G and B intensities for that sample, on a
> contiguous sample space thingy.
>   Can I do this for alpha?  How do I do it programatically?  I don't
> want the user having to drag his mouse around just to set 'no rain'
> to be transparent.

You can do it with a ScalarMap to Display.RGBA. The
getControl() method for this ScalarMap will return a
ColorAlphaControl, and you can call its setTable() method
to set the 4-component lookup table for red, green, blue
and alpha. See Sections 4.6 and 4.11 of the tutorial for
more details.

Cheers,
Bill
----------------------------------------------------------
Bill Hibbard, SSEC, 1225 W. Dayton St., Madison, WI  53706
hibbard@xxxxxxxxxxxxxxxxx  608-263-4427  fax: 608-263-6738
http://www.ssec.wisc.edu/~billh/vis.html

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