[Radiance-general] Interpolate BSDFs

Andrew McNeil amcneil at lbl.gov
Wed Feb 19 10:59:38 PST 2014


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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