RE: [Algorithms] Solid angle calculation

[Tom F. <to...@mu...>]

We know what sinc _is_ - Joris even gave the code for it. The question is
why is it being used here?

Tom Forsyth - purely hypothetical Muckyfoot bloke.

This email is the product of your deranged imagination,
and does not in any way imply existence of the author.

> -----Original Message-----
> From: Nick Pelling [mailto:NPe...@cl...]
> Sent: 18 September 2002 11:42
> To: gda...@li...
> Subject: RE: [Algorithms] Solid angle calculation
> 
> 
> sinc() is actually a well-known maths function, and is often 
> used in code
> for rescaling / resampling.
> 
> Search for "sinc function" on Google, and you'll hit loads of 
> maths sites
> explaining it, such as:
> 
> http://mathworld.wolfram.com/SincFunction.html
> 
> Cheers, .....Nick Pelling.....
> 
> -----Original Message-----
> From: Tom Forsyth [mailto:to...@mu...]
> Sent: 16 September 2002 12:51
> To: Joris Mans; gda...@li...
> Subject: RE: [Algorithms] Solid angle calculation
> 
> 
> I assumed that was a typo, and they mean "sine(theta)". But I 
> didn't worry
> about it too hard since, using cube-maps and just ignoring 
> the spherical
> distortion (i.e. every sample is evenly weighted) seemed to 
> work just fine -
> at least to within the tolerance of my eye :-). It also bins 
> all the angle
> stuff and uses the SH components directly (since you already 
> have x,y,z to
> plug into the component calculations), so there's no trig 
> anywhere in any
> equations. Which is very good news for speed.
> 
> 
> Tom Forsyth - purely hypothetical Muckyfoot bloke.
> 
> This email is the product of your deranged imagination,
> and does not in any way imply existence of the author.
> 
> > -----Original Message-----
> > From: Joris Mans [mailto:jor...@pa...]
> > Sent: 12 September 2002 02:17
> > To: gda...@li...
> > Subject: [Algorithms] Solid angle calculation
> > 
> > 
> > Hi
> > 
> > I am currently trying to understand/implement the integration scheme
> > used in "An efficient rep. for Irradiance env maps" and I 
> > think my math
> > skills have some holes in them, because I don't understand 
> the formula
> > for calculating the solid angle.
> > This is the c sample code:
> > 
> > domega = (2*PI/width)*(2*PI/width)*sinc(theta) ;
> > 
> > I understand where the / width comes from since you are 
> integrating in
> > steps of 1/width over the sphere, but I fail to understand what
> > sinc(theta) means. 
> > 
> > FYI:
> > 
> > float sinc(float x) {               /* Supporting sinc function */
> >   if (fabs(x) < 1.0e-4) return 1.0 ;
> >   else return(sin(x)/x) ;
> > }
> > 
> > How does this term calculate the solid angle?
> > 
> > Thanks
> > 
> > Joris
> > 
> > 
> > 
> > -------------------------------------------------------
> > In remembrance
> > www.osdn.com/911/
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> 
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