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