Re: 3-D cliping

• To: Bill Hibbard <hibbard@xxxxxxxxxxxxxxxxx>
• Subject: Re: 3-D cliping
• From: Don Murray <dmurray@xxxxxxxxxxxxxxxx>
• Date: Thu, 25 Oct 2001 14:57:39 -0600

Hi All-

First, thanks to Bill for doing this.  I've added
a couple of notes below.

Bill Hibbard wrote:
> 
> I just but a new release of VisAD on the server, that
> supports 3-D clipping. See visad/examples/Test35.java
> for an example.
> 
> Applications can set up to six arbitrarily oriented clipping
> planes using a new method of DisplayRendererJ3D:
> 
>   /** define a clipping plane in (XAxis, YAxis, ZAxis) space
>       plane number must be in (0, ..., 5)
>       clip plane defined by ax + by + cz + d <= 0
>   */
>   public void setClip(int plane, boolean enable, float a, float b, float c, 
> float d)
>          throws VisADException;
> 
> This only clips data depictions, not axis scales etc.
> From Test35.java, to clip to the usual box (i.e., x, y and
> z values in the range -1.0 to +1.0), do:
> 
>   DisplayRendererJ3D dr = (DisplayRendererJ3D) display.getDisplayRenderer();
>   dr.setClip(0, true,  1.0f,  0.0f,  0.0f, -1.0f);
>   dr.setClip(1, true, -1.0f,  0.0f,  0.0f, -1.0f);
>   dr.setClip(2, true,  0.0f,  1.0f,  0.0f, -1.0f);
>   dr.setClip(3, true,  0.0f, -1.0f,  0.0f, -1.0f);
>   dr.setClip(4, true,  0.0f,  0.0f,  1.0f, -1.0f);
>   dr.setClip(5, true,  0.0f,  0.0f, -1.0f, -1.0f);
> 

Comments:

1) In the snippet above, you might want to use something slightly
smaller than -1.0f (e.g. -1.01 or -1.1).  On my Windows machine,
I found that anything rendered in Z plane rendered at 1.0 or
-1.0 would waft in and out of the display as it was rotated.
Changing the -1.0 to -1.01f fixed this.

2) Clipping only works if you are using a version of Java3D
that is >= 1.2.  The code determines this automagically 
and if you are running with Java3D 1.1.x and try to call setClip, 
a DisplayException will be thrown.  So, let the buyer beware
when you use this method.

Don
*************************************************************
Don Murray                               UCAR Unidata Program
dmurray@xxxxxxxxxxxxxxxx                        P.O. Box 3000
(303) 497-8628                              Boulder, CO 80307
http://www.unidata.ucar.edu/staff/donm
*************************************************************

• References:
  • 3-D cliping
    • From: Bill Hibbard