Re: Specific alpha values

• Subject: Re: Specific alpha values
• From: Ugo Taddei <p6taug@xxxxxxxxxxxxxxxxx>
• Date: Tue, 22 May 2001 15:43:39 +0200

Hi Andrew,

> Hi there,
> 
>   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.
> 
> thanks in advance,


Though I'm sure Bill's approach would work, you might considering
setting the 0 values to Float.NaN (Not-a-number).

This would make them invisible (or transparent, I'm not sure).

Cheers,

Ugo

• References:
  • Specific alpha values
    • From: Andrew Donaldson