Re: how to determine visible data range?

• To: Tomas Pluskal <pluskal@xxxxxxx>
• Subject: Re: how to determine visible data range?
• From: Don Murray <dmurray@xxxxxxxxxxxxxxxx>
• Date: Tue, 20 Jun 2006 08:00:44 -0600

Hi Tomas-

Tomas Pluskal wrote:

I'm using VisAD library to visualize a large data sets of mass spectrometry data in 3D. I would like to resample the visible part of the data set according to the current zoom (scale), to get a primitive "level of detail" support. I have added a listener for the projection control, so I know when the scale changes and using MouseBehaviorJ3D.unmake_matrix() I can get the current scale, rotation and translation values. But I don't know how to determine the subset of the domain (X/Y axes), which is currently visible.

Is there any simple way how to do it?
Thanks!

We do this by using a projection listener to listen for
changes and then sampling the screen at the corners to determine
the XY bounds.  You can use the MouseBehavior.findRay(x,y) method
to figure out what the VisAD X/Y/Z values are at screen xy coordinates.
Use DisplayImpl.getComponent().getBounds() to figure out how large
your canvas is and then sample at the 4 corners.  Then for
each point, use the ScalarMap.inverseScaleValues() method
to convert the x and y values to the scalar values of
the map.  That should give you the limits of the visible
portion of your screen that you can use for resampling.
If you have a display side coordinate system (e.g. map projection),
your mappings are not necessarily linear.  In that case, we sample
at 9 points (3 across the top, middle and bottom) on the screen
to get a more representative bounds.

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


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