[Radiance-general] Interpolate BSDFs

[David Griffiths]

Andy

Thank you for this.  I had the -t and -p options back to front (literally)!  When I use your settings for front transmission I now get perfect agreement.

Kind regards

David Griffiths



On 19 Feb 2014, at 18:59, Andrew McNeil <amcneil at lbl.gov> wrote:

Hi David,

I'm getting near perfect agreement between the two programs.
Make sure you understand the front/back conventions for bsdf2rad:

This gives back transmission for the normal patch:
bsdf2rad -t mybsdf.xml 0 0 > myrad.rad

This gives back reflection for the normal patch:
bsdf2rad -p mybsdf.xml 0 0 > myrad.rad

This gives front transmission for the normal patch:
bsdf2rad -p mybsdf.xml 180 0 > myrad.rad

This gives front reflection for the normal patch:
bsdf2rad -t mybsdf.xml 180 0 > myrad.rad

And yes, when your theta is greater than 90 (to get front values) the current behavior is that -t  gives reflection and -p gives transmission (not sure if this is expected!)

If you're still not getting agreement, send me your xml file in a separate email.

Andy



On Tue, Feb 18, 2014 at 9:54 PM, Greg Ward <gregoryjward at gmail.com> wrote:
No, I have no idea why they should disagree.  Maybe Andy has time to compare his code to the hemispherical scattering report I'm making in bsdf2rad:

			fprintf(stderr, "Hemispherical %s: %.3f\n",
				(output_orient > 0 ? "reflection" : "transmission"),
				SDdirectHemi(idir, SDsampSp|SDsampDf |
						(output_orient > 0 ?
						 SDsampR : SDsampT), &myBSDF));

It's possible that Andy isn't using the same set of flags, and is missing some of the energy or counting both sides rather than just hemispherical transmission.

Cheers,
-Greg

> From: David Griffiths <david.griffiths at solaveil.co.uk>
> Date: February 19, 2014 12:12:31 AM GMT+01:00
> 
> Greg
> 
> I am sure there must be something simple I am missing but do you know why I would get significantly lower hemispherical transmittance figures from bsdf2rad than from BSDFviewer (e.g. for phi 0 theta 0 in bsdf2rad as compared to  incident patch 1 in BSDFviewer)?
> 
> Kind regards
> 
> David Griffiths
> M +44 (0) 7785 700160
> W solaveil.co.uk
> 
> 
> On 17 Feb 2014, at 21:55, Greg Ward <gregoryjward at gmail.com> wrote:
> 
> Hi Germán,
> 
> You can compute the total hemispherical transmittance for a particular incident angle using the bsdf library, which is also reported to the standard error by bsdf2rad when you run it.
> 
> Best,
> -Greg

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