Re: [Algorithms] Problem with Woo's "Fast Ray-Box Intersection"

[Klaus H. <k_h...@os...>]

Never mind... The VC+ 6 Debugger just displayed a completely wrong
floating-point value. A simple printf() displayed the correct one. The
helped me to make the code work... finally. Just had to subtract/add a small
epsilon from/to the AABB's min/max points.

Niki

----- Original Message -----
From: Klaus Hartmann <k_h...@os...>
To: <gda...@li...>
Sent: Saturday, August 26, 2000 8:25 AM
Subject: [Algorithms] Problem with Woo's "Fast Ray-Box Intersection"


> Hi all,
>
> I have a problem that I don't understand. I have the following line of
> source in my implementation of Woo's "Fast Ray-Box Intersection":
>
> hitpoint[i] = rayOrg[i] + maxT[whichPlane] * rayDir[i];
>
> hitpoint, rayOrg, maxT, and rayDir are all arrays with three
floating-point
> values (indices 0 to 2). Now here are some values:
>
> i = 2 (which is a valid index)
> whichPlane = 0 (also a valid index)
> rayOrg[i] = -2
> maxT[whichPlane] = 2.82843
> rayDir[i] = 0.707107
>
> These are all very valid values, and the result should now be:
> hitpoint[i] = -2 + 2.82843 * 0.707107 = 2.65201e-06
>
> However, the debugger says, that
> hitpoint[i] = -6.8457097e-008
>
> Okay, so I thought that maybe this is a precision problem. I tried
doubles,
> but I got the same wrong value. Then I thought, that there might be
> something wrong hitpoint[i], so I replaced that with a local double
> variable, but the result is still wrong.
>
> Why? I cannot believe that 2.65201e-06 is too small to be represented as a
> double-precision floating-point value. Can someone explain this to me? Or
do
> you see a bug in the above C line? If you don't believe me, then I'm very
> well willing to upload the code (very small), and you can step through it,
> and see for yourselves.
>
> Niki
>
>
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