Re: Isect weirdness

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Angus Dorbie (dorbie++at++bitch.reading.sgi.com)
Sun, 8 Dec 1996 20:34:10 +0000

On Dec 4, 7:06pm, Scott McMillan wrote:
> Subject: Isect weirdness
> I have been experiencing some weird behavious using isect....
>
> When I have a normalized direction vector, and a VERY small length
> (on the order of 1e-9) Performer outputs a warning message:
>
> PF Warning/Usage: No inverse: singular matrix
>

Looks like this could be due to floating point rounding, do you really
need this size of vector?

> When I have a zero length direction vector and a zero length it
> doesn't complain at all.
>

There's no such thing, it's probably defaulting to something sane,
or maybe you get lucky with the code.

> Anybody know why it is doing this? My guess would be that isect
> checks for zero length dir vectors in the pfSegSet and handles them
> appropriately, but it can't deal with the small numbers that aren't
> exactly zero but should be????

Sounds like a good guess to me.

>-- End of excerpt from Scott McMillan

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