[info-performer] bounding sphere with non-uniform scaling

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From: John Kelso (kelso++at++bev.net)
Date: 07/28/2004 15:03:20

Hi all,

I have a file that's the output of a simulation, containing about 2500
points. The x and y don't have much of a range as they go across z. We
wanted to use the scale pseudo-loader to make the data display something
we could actually see.

If I run my little bounding program:

> dpf-bounds test.pfb 2>/dev/null
bounding sphere radius = 78.796997
  (Performer's pfNode->getSphere returns radius = 78.796997)
X: 0.000000 - 0.000100, delta: 0.000100 center: 0.000050
Y: 0.000200 - 0.014889, delta: 0.014689 center: 0.007544
Z: -35.424000 - 122.169998, delta: 157.593998 center: 43.372999

the bounding sphere I calculate is based on a sphere around the data's
bounding box. The one reported by Performer is on the next line in
parentheses.

If I scale it mostly in X I get this:
> dpf-bounds test.pfb.1000000,100,1.scale 2>/dev/null
bounding sphere radius = 93.297958
  (Performer's pfNode->getSphere returns radius = 78797000.000000)
X: 0.100000 - 100.000000, delta: 99.900000 center: 50.050000
Y: 0.020000 - 1.488900, delta: 1.468900 center: 0.754450
Z: -35.424000 - 122.169998, delta: 157.593998 center: 43.372999

It looks like the radius returned by Performer uses just the X scale
value. The data ranges look OK.

If I switch the X and Z scales:
> dpf-bounds test.pfb.1,100,1000000.scale 2>/dev/null
bounding sphere radius = 78797000.000000
  (Performer's pfNode->getSphere returns radius = 78797000.000000)
X: 0.000000 - 0.000100, delta: 0.000100 center: 0.000050
Y: 0.020000 - 1.488900, delta: 1.468900 center: 0.754450
Z: -35424000.000000 - 122170000.000000, delta: 157594000.000000 center:
43373000.000000

Performer returns the same radius, but it's correct.

Is this correct behavior for the Performer bounding sphere? Am I just
using it wrong? How does this affect culling and other activities that
use the bounding sphere? Does perfly use it to size and center the
object?

I can send the data as a pfb if it'll help.

Thanks,

-John

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