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.\" RCSid "$Id: findglare.1,v 1.4 2007/09/04 17:36:40 greg Exp $"
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.TH FINDGLARE 1 11/15/93 RADIANCE
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.SH NAME
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findglare - locate glare sources in a RADIANCE scene
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.SH SYNOPSIS
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.B findglare
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[
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.B \-v
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][
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.B "\-ga angles"
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][
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.B "\-t threshold"
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][
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.B "\-r resolution"
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][
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.B \-c
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][
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.B "\-p picture"
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][
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view options
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] [[
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rtrace options
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]
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.B octree
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]
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.SH DESCRIPTION
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.I Findglare
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locates sources of glare in a specific set of horizontal directions
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by computing luminance samples from a RADIANCE picture and/or octree.
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.I Findglare
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is intended primarily as a preprocessor for glare calculation
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programs such as
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.I glarendx(1),
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and is usually accessed through the executive script
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.I glare(1).
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.PP
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If only an octree is given,
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.I findglare
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calls rtrace to compute the samples it needs.
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If both an octree and a picture are specified,
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.I findglare
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calls rtrace only for samples that are outside the frame of
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the picture.
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If
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.I findglare
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does not have an octree and the picture does not completely cover
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the area of interest, a warning will be issued and everything
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outside the picture will be treated as if it were black.
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It is preferable to use a picture with a fisheye view
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and a horizontal and vertical size of at least 180 degrees (more
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horizontally if the
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.I \-ga
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option is used -- see below).
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Note that the picture file must contain correct view specifications,
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as maintained by
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.I rpict(1),
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.I rvu(1),
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.I pfilt(1)
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and
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.I pinterp(1).
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Specifically,
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.I findglare
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will not work on pictures processed by
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.I pcompos(1)
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or
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.I pcomb(1).
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It is also essential to give the proper rtrace options when an
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octree is used so that the calculated luminance values are correct.
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.PP
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The output of
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.I findglare
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is a list of glare source directions, solid angles and average
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luminances, plus a list of indirect vertical illuminance values
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as a function of angle.
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Angles are measured in degrees from the view center,
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with positive angles to the left and negative angles to the right.
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.PP
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By default,
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.I findglare
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only computes glare sources and indirect vertical illuminance
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for the given view (taken from the picture if none is specified).
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If the view direction is not horizontal to begin with
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(ie. perpendicular to the view up vector),
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.I findglare
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will substitute the closest horizontal direction as its view
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center.
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The
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.I \-ga
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option can be used to specify a set of directions to consider
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about the center of view.
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This specification is given by a starting angle, ending angle, and
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step angle like so:
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.nf
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start-end:step
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.fi
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All angles must be whole degrees within the range 1 to 180.
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Multiple angle ranges may be separated by commas, and individual
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angles may be given without the ending and step angles.
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Note that
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.I findglare
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will complain if the same angle is given twice either explicitly
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or implicitly by two ranges.
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.PP
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.I Findglare
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normally identifies glare sources as directions that are
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brighter than 7 times the average luminance level.
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It is possible to override this determination by giving an
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explicit luminance threshold with the
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.I \-t
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option.
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It usually works best to use the 'l' command within
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.I ximage(1)
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to decide what this value should be.
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Alternatively, one can use the 't' command within
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.I rvu(1).
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The idea is to pick a threshold that is well above the average level
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but smaller than the source areas.
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.PP
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If the sources in the scene are small, it may be necessary to
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increase the default sample resolution of
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.I findglare(1)
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using the
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.I \-r
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option.
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The default resolution is 150 vertical samples and a proportional number
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of horizontal samples.
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If besides being small, the sources are not much brighter than the
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threshold, the
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.I \-c
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flag should be used to override
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.I findglare's
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default action of absorbing small sources it deems to be
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insignificant.
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.PP
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The
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.I \-v
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flag switches on verbose mode, where
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.I findglare
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reports its progress during the calculation.
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.SH EXAMPLE
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To calculate the glare sources in the image "scene.hdr":
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.IP "" .2i
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findglare \-p scene.hdr > scene.glr
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.PP
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To compute the Guth visual comfort probability from this result:
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.IP "" .2i
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glarendx \-t guth_vcp scene.glr
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.PP
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To compute the glare for a set of angles around the view "good.vp"
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from the octree "scene.oct" using an ambient level of .1:
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.IP "" .2i
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findglare \-vf good.vp \-ga 10-60:10 \-av .1 .1 .1 scene.oct > scene.glr
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.SH AUTHOR
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Greg Ward
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.SH ACKNOWLEDGEMENT
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Work on this program was initiated and sponsored by the LESO
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group at EPFL in Switzerland.
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.SH "SEE ALSO"
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getinfo(1), glare(1), glarendx(1), pfilt(1), rpict(1), rtrace(1),
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rvu(1), xglaresrc(1), ximage(1)
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