[Radiance-general] Attempt to illuminate Paul Debevec's rnl_scene.rad with a hemispherical HDR image of the sky

[kyle konis]

Hello Claus,

Thanks for the response, both on the HDRI list and here. I've never
got into custom .cal files, but looks like the place to start to get
exactly what i want.

I quickly read through some of the HDRshop tutorials on: http://www.hdrshop.com/

There are many interesting and useful tools (including scripting) ....
And perhaps the "Panoramic Image Conversion" tool is what you are
referring to?

....At the conceptual level, the step i am confused with is
identifying the appropriate virtual object in Radiance to map my HDR
environment to.

Paul uses an inward-pointing box, as in:

###############################################################
# specify a large inward-pointing box to be mapped with the HDR environment

!genbox env_glow boxenv 500 500 500 -i | xform -t -250 -18 -250
###############################################################

All surfaces of the box contribute light.

Because i only have captured light data from the horizon up, and dont
care (at this stage) about the group plane, it would seem that i
should start with a box that encompasses a hemisphere that is
positioned on the xy plane.

Assuming this step is correct, i would then aim to map the non-zero
pixels in my hemispherical image to the surfaces of that box
(effectively stretching the circle into a rectangle).

Alternatively, i could also try to map to a hemisphere, but then there
is the issue of what to do with the "black" pixels which make up the
corners of the HDR image.

best,

-Kyle




On Sun, Oct 14, 2012 at 12:23 PM, Claus Brøndgaard Madsen
<cbm at create.aau.dk> wrote:
>
>
> Hi Kyle,
>
> Solving your problem is easy and not so easy.
>
> There will be some overlap between this response and my response To your other post, but for completeness...
>
> The easiest solution would be to re-map your hemispherical sky image to angular mapping that Debevec always prefers. I, myself, prefer the lat-long mapping, so I have written my own mapping .cal file. Writing such a .Cal is easy but you have to know what you are doing and there can be some debugging (trial and error) involved.
>
> In order to remap you sky view to an angular mapping it would be simple and easy to use the HDRshop progam (www.hdrshop.com), but there is no longer a free 1.0 version. Versions for academia are not too expensive though.
>
> Best
> Claus
>
>
>
>
> Claus B. Madsen
> AD:MT/AAU
>
>
> On 14/10/2012, at 12.17, "kyle konis" <kskonis at gmail.com> wrote:
>
>> Dear list,
>>
>> I am attempting to illuminate Paul Debevec's rnl_scene.rad with a
>> hemispherical HDR image of a dynamic sky.
>>
>> After the tutorial in http://www.pauldebevec.com/RNL/Source/
>>
>> I have succeeded in simply substituting in my image, but because it is
>> a 180-degree fisheye image (zenith view of sky) rather than a light
>> probe, i am encountering some issues with the resulting "reality" of
>> the output image.
>>
>> I would appreciate suggestions for how to properly map this image data
>> to a hemisphere (i.e. sky) in radiance to enable the image to serve
>> properly as a light source.
>>
>> I have included the relevant code below, and sample images on a
>> temporary webpage:
>>
>> https://sites.google.com/site/konisskytemp/
>>
>>
>> I would appreciate any suggestions!
>>
>> -Kyle
>>
>>
>> ### Here is the relevant description of the lighting environment ( i
>> have only changed the image file name to source my 1350 x 1350 px
>> cropped sky image)
>>
>> ################################################################
>> #
>> #  Lighting Environment
>> #
>> ################################################################
>>
>> # specify the probe image and how it is mapped onto geometry
>>
>> void colorpict hdr_env
>> 7 red green blue cropped.hdr angmap.cal sb_u sb_v
>> 0
>> 0
>>
>> # specify a "glow" material that will use this image
>>
>> hdr_env glow env_glow
>> 0
>> 0
>> 4 1 1 1 0
>>
>> # specify a large inward-pointing box to be mapped with the HDR environment
>>
>> !genbox env_glow boxenv 500 500 500 -i | xform -t -250 -18 -250
>>
>>
>>
>>
>>
>> ################################################################
>> ### and here is angmap.cal
>> ################################################################
>>
>> {
>> angmap.cal
>>
>> Convert from directions in the world to coordinates on the angular sphere image
>>
>> -z is forward (outer edge of sphere)
>> +z is backward (center of sphere)
>> +y is up (toward top of sphere)
>> }
>>
>> sb_u = 0.5 + DDx * r;
>> sb_v = 0.5 + DDy * r;
>>
>> r = 0.159154943*acos(DDz)/sqrt(DDx*DDx + DDy*DDy);
>>
>> DDy = Py*norm;
>> DDx = Px*norm;
>> DDz = Pz*norm;
>>
>> norm = 1/sqrt(Py*Py + Px*Px + Pz*Pz);
>>
>>
>>
>>
>> ### Any suggestions for solutions would be appreciated
>>
>> I assume that i need to map the image to a hemisphere (representing
>> the sky dome) rather than a box
>>
>> perhaps passing the image as a glow rather than the standard sky glow?
>>
>> skyfunc glow skyglow
>> 0
>> 0
>> 4 1.000 1.000 1.000 0
>> skyglow source sky
>> 0
>> 0
>> 4 0 0 1 180
>>
>> Or to a sphere?
>>
>>
>>
>> And i assume that i need a different angmap.cal file, given that this
>> was written to interpret light probe images . . . and not
>> hemispherical fisheye images
>>
>> _______________________________________________
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>
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