genskyvec and hdr

Hi everyone,

Is there a way to run genskyvec with an HDR sky image? If yes, how? I could not come up with the right solution.

Thanks,
Mehlika

Hi Mehlika,

The genskyvec program is designed to work with gendaylit and gensky input, only. That isn't to say you shouldn't be able to generate an equivalent output from an HDR capture of the sky dome, but genskyvec isn't going to be much help with that. You are looking at a manual process until and unless someone gets around to automating it.

Here are some of the necessary steps:

1) Create a Radiance description of a scene using your captured sky as a colorpict input with the appropriate fisheye mapping.
2) Extract the $rhcal variable from genskyvec.pl, which defines the Reinhart sky sampling needed.
3) Assign the MF constant to the desired Reinhart subdivision resolution (default 4 in genskyvec).
4) Call cnt with the number of sky patches as given by the Rmax constant defined in $rhcal and the number of samples per patch (16 in genskyvec but you may need more if you're trying to resolve the sun).
5) Pipe the output of cnt into rcalc and rtrace as done in the $tregcommand variable in genskyvec.pl.
6) The output of rtrace goes into total to sum patch values together, and this basically produces your desired vector, minus the ground plane.
7) Insert a ground plane triple at the beginning based on the expected ground brightness (irradiance times reflectance over pi) and you're done.

-Greg

···

From: Mehlika Inanici <[email protected]>
Date: February 23, 2013 1:57:48 PM PST

Hi everyone,

Is there a way to run genskyvec with an HDR sky image? If yes, how? I could not come up with the right solution.

Thanks,
Mehlika

Thanks Greg. I was thinking of a quick and definitely dirty way of transforming fisheye into panorama, which will make the parsing much easier. I will try both ways. Obviously, your process will be more precise. As always, your help is greatly appreciated.

Mehlika

···

On Sun, 24 Feb 2013, Gregory J. Ward wrote:

Hi Mehlika,

The genskyvec program is designed to work with gendaylit and gensky input, only. That isn't to say you shouldn't be able to generate an equivalent output from an HDR capture of the sky dome, but genskyvec isn't going to be much help with that. You are looking at a manual process until and unless someone gets around to automating it.

Here are some of the necessary steps:

1) Create a Radiance description of a scene using your captured sky as a colorpict input with the appropriate fisheye mapping.
2) Extract the $rhcal variable from genskyvec.pl, which defines the Reinhart sky sampling needed.
3) Assign the MF constant to the desired Reinhart subdivision resolution (default 4 in genskyvec).
4) Call cnt with the number of sky patches as given by the Rmax constant defined in $rhcal and the number of samples per patch (16 in genskyvec but you may need more if you're trying to resolve the sun).
5) Pipe the output of cnt into rcalc and rtrace as done in the $tregcommand variable in genskyvec.pl.
6) The output of rtrace goes into total to sum patch values together, and this basically produces your desired vector, minus the ground plane.
7) Insert a ground plane triple at the beginning based on the expected ground brightness (irradiance times reflectance over pi) and you're done.

-Greg

From: Mehlika Inanici <[email protected]>
Date: February 23, 2013 1:57:48 PM PST

Hi everyone,

Is there a way to run genskyvec with an HDR sky image? If yes, how? I could not come up with the right solution.

Thanks,
Mehlika

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