man/man1/rxfluxmtx.1

.\" RCSid "$Id: rxfluxmtx.1,v 1.1 2025/10/23 23:34:59 greg Exp $"
.TH RXFLUXMTX 1 10/23/2025 RADIANCE
.SH NAME
rxfluxmtx - compute flux transfer matrix(es) for RADIANCE scene
.SH SYNOPSIS
.B rxfluxmtx
[
.B \-W
] [
.B "rcontrib options"
]
.B "{ sender.rad | view | - }"
.B receivers.rad
.B "[ -i system.oct ]"
.B "[ system.rad .. ]"
.SH DESCRIPTION
.I rxfluxmtx
samples rays uniformly over the surface given in
.I sender.rad
and records rays arriving at surfaces in the file
.I receivers.rad,
producing a flux transfer matrix per receiver.
A system octree to which the receivers will be appended may be given with a
.I \-i
option following the receiver file.
Additional system surfaces may be given in one or more
.I system.rad
files, which are compiled before the receiver file into an octree used
to perform the simulation.
.PP
If a single hyphen ('-') is given in place of the view or sender file, then
.I rxfluxmtx
computes matrix rows based upon the provided ray sample origins and directions,
which may be surface normals if the
.I \-I+
option is applied.
The
.I \-y
option is required to specify the number of output rows for pass-through mode.
.PP
Alternatively, a view specification may be given on the command-line
to produce coefficient picture output, in which case both the
.I \-x
and
.I \-y
options must be present to set the desired picture dimensions.
The related
.I \-pj,
.I \-pd,
and
.I \-pa
options may be used to set the pixel jitter, depth-of-field, and
aspect ratio, respectively.
This avoids the need to call
.I vwrays(1),
as required by
.I rfluxmtx.
.PP
The
.I \-W+
option turns on verbose mode, and the
.I \-t
option sets the number of seconds between progress reports, similar to
.I rcontrib(1).
However, the
.I rcontrib
options
.I \-p,
.I \-b,
.I \-bn,
.I \-m,
and
.I \-M
options are controlled by
.I rxfluxmtx
and may not be set by the user.
.PP
The sample count, unless set by the
.I \-c
option, defaults to 10000 when a sender file is given, or to 1 for 
view and pass-through modes.
.SH VARIABLES
The sender and receiver scene files given to
.I rxfluxmtx
contain controlling parameters in special comments of the form:
.nf

        #@rxfluxmtx variable=value ..
or:
        #@rfluxmtx variable=value ..

.fi
At minimum, both sender and receiver must specify one of the
hemisphere sampling types, and there must be at least
one surface in each file.
.TP 10n
.BI h =u
Set hemisphere sampling to "uniform," meaning a single bin
of (cosine-distributed) samples.
In the case of distant "source" primitives, this is the only
sampling method that supports arbitrary receiver sizes.
The other methods below require a full hemispherical source.
.TP
.BI h =kf
Divide the hemisphere using the LBNL/Klems "full" sampling basis.
(Use "h=-kf" for left-handed coordinates.)
.TP
.BI h =kh
Divide the hemisphere using the LBNL/Klems "half" sampling basis.
(Use "h=-kh" for left-handed coordinates.)
.TP
.BI h =kq
Divide the hemisphere using the LBNL/Klems "quarter" sampling basis.
(Use "h=-kq" for left-handed coordinates.)
.TP
.BI h =rN
Divide the hemisphere using Reinhart's substructuring of the Tregenza
sky pattern with
.I N
divisions in each dimension.
If it is not given,
.I N
defaults to 1, which is just the Tregenza sky.
(Use "h=-rN" for left-handed coordinates.)
.TP
.BI h =cie
Divide the hemisphere into CIE sky scanner directions, which is
similar to Tregenza but with different starting azimuths and
reversing row direction at each new altitude.
(Use "h=-cie" for left-handed coordinates.)
.TP
.BI h =scN
Subdivide the hemisphere using the Shirley-Chiu square-to-disk mapping with an
.I NxN
grid over the square.
(Use "h=-scN" for left-handed coordinates.)
.TP
.BI u =[-]{X|Y|Z|ux,uy,uz}
Orient the "up" direction for the hemisphere using the indicated axis or direction
vector.
.TP
.BI o =output_spec
Send the matrix data for this receiver to the indicated file specification.
Single or double quotes may be used to contain strings with spaces, and
the usual "%s" and "%d" formats incorporate the modifier name and/or
bin number, as with
.I rcontrib.
Command (piped) output is not supported.
.PP
If no output_spec directive is given, it must be specified by a
.I \-o
setting on the command-line, since output to stdout is not supported.
The input and output file formats are controlled by the
.I \-fio
option, which may use a single letter for identical i/o formats.
The input format matters only in pass-through mode, for which
ASCII input is supported.
ASCII output is unsupported, since it interferes with
efficient recovery in the
.I \-r
mode.
The default setting is
.I \-faf.
.PP
In normal execution, only a single sender surface is sampled, but it may be
comprised of any number of subsurfaces, as in a triangle mesh or similar.
The surface normal will be computed as the average of all the constituent
subsurfaces.
The subsurfaces themselves must be planar, thus only
.I polygon
and
.I ring
surface primitives are supported.
Other primitives will be silently ignored and will have no effect on the calculation.
.PP
In the receiver file, the
.I source
primitive is supported as well, and multiple receivers (and multiple output
matrices) may be identified by different modifier names.
(Make sure that surfaces using the same modifier are grouped together,
and that the modifiers are unique and not used elsewhere in the
scene description.)\0
Though it may be counter-intuitive, receivers are often light sources,
since samples end up there in a backwards ray-tracing system such as RADIANCE.
When using local geometry, the overall aperture shape should be close to flat.
Large displacements may give rise to errors due to a convex receiver's
larger profile at low angles of incidence.
.PP
Rays always emanate from the back side of the sender surface and arrive at the
front side of receiver surfaces.
In this way, a receiver surface may be reused as a sender in a subsequent
.I rxfluxmtx
calculation and the resulting matrices will concatenate properly.
(Note that it is important to keep receiver surfaces together, otherwise a
"duplicate modifier" error will result.)\0
.SH EXAMPLES
To generate a flux transfer matrix connecting input and output apertures
on a light pipe:
.IP "" .2i
rxfluxmtx int_aperture.rad ext_aperture.rad lpipe.rad > lpipe.mtx
.PP
To generate a set of DC view component pictures with 9 jittered samples/pixel:
.IP "" .2i
rxfluxmtx -vf v1.vf -x 512 -y 512 -c 9 -pj .8 -fc reinhart_M4.rad -i scene1.oct
.PP
To compute a workplane irradiance matrix for each window in a space:
.IP "" .2i
rxfluxmtx -faf - windows_kf.rad -i scene2.oct < workplane_pts.txt
.SH NOTES
The main differences between
.I rfluxmtx(1)
and
.I rxfluxmtx
is that the latter does not run a separate
.I rcontrib
process.
Instead, it relies on a unix-only C++ class definition that offers full
control over i/o.
This allows an unlimited number of receivers, a
.I \-r
recovery option, and simplifies internal operations.
.SH AUTHOR
Greg Ward
.SH "SEE ALSO"
genBSDF(1), getinfo(1), pvsum(1), rcalc(1), rcollate(1), rcomb(1), rcontrib(1),
rcrop(1), rfluxmtx(1), rmtxop(1), vwrays(1), wrapBSDF(1)
Revision:	1.2
Committed:	Fri Oct 24 16:52:14 2025 UTC (2 weeks ago) by greg
Branch:	MAIN
CVS Tags:	HEAD
Changes since 1.1:	+17 -8 lines
Log Message:	docs(rxfluxmtx): wording corrections and clarifications
#	User	Rev	Content
1	greg	1.2	.\" RCSid "$Id: rxfluxmtx.1,v 1.1 2025/10/23 23:34:59 greg Exp $"
2	greg	1.1	.TH RXFLUXMTX 1 10/23/2025 RADIANCE
3			.SH NAME
4			rxfluxmtx - compute flux transfer matrix(es) for RADIANCE scene
5			.SH SYNOPSIS
6			.B rxfluxmtx
7			[
8			.B \-W
9			] [
10			.B "rcontrib options"
11			]
12			.B "{ sender.rad \| view \| - }"
13			.B receivers.rad
14			.B "[ -i system.oct ]"
15			.B "[ system.rad .. ]"
16			.SH DESCRIPTION
17			.I rxfluxmtx
18			samples rays uniformly over the surface given in
19			.I sender.rad
20			and records rays arriving at surfaces in the file
21			.I receivers.rad,
22			producing a flux transfer matrix per receiver.
23			A system octree to which the receivers will be appended may be given with a
24			.I \-i
25			option following the receiver file.
26			Additional system surfaces may be given in one or more
27			.I system.rad
28			files, which are compiled before the receiver file into an octree used
29			to perform the simulation.
30			.PP
31			If a single hyphen ('-') is given in place of the view or sender file, then
32			.I rxfluxmtx
33			computes matrix rows based upon the provided ray sample origins and directions,
34			which may be surface normals if the
35			.I \-I+
36			option is applied.
37			The
38			.I \-y
39			option is required to specify the number of output rows for pass-through mode.
40			.PP
41			Alternatively, a view specification may be given on the command-line
42			to produce coefficient picture output, in which case both the
43			.I \-x
44			and
45			.I \-y
46			options must be present to set the desired picture dimensions.
47			The related
48			.I \-pj,
49			.I \-pd,
50			and
51			.I \-pa
52			options may be used to set the pixel jitter, depth-of-field, and
53			aspect ratio, respectively.
54			This avoids the need to call
55			.I vwrays(1),
56			as required by
57			.I rfluxmtx.
58			.PP
59			The
60			.I \-W+
61			option turns on verbose mode, and the
62			.I \-t
63			option sets the number of seconds between progress reports, similar to
64			.I rcontrib(1).
65			However, the
66			.I rcontrib
67			options
68			.I \-p,
69			.I \-b,
70			.I \-bn,
71			.I \-m,
72			and
73			.I \-M
74			options are controlled by
75			.I rxfluxmtx
76			and may not be set by the user.
77			.PP
78			The sample count, unless set by the
79			.I \-c
80			option, defaults to 10000 when a sender file is given, or to 1 for
81			view and pass-through modes.
82			.SH VARIABLES
83			The sender and receiver scene files given to
84			.I rxfluxmtx
85			contain controlling parameters in special comments of the form:
86			.nf
87
88			#@rxfluxmtx variable=value ..
89			or:
90			#@rfluxmtx variable=value ..
91
92			.fi
93			At minimum, both sender and receiver must specify one of the
94			hemisphere sampling types, and there must be at least
95			one surface in each file.
96			.TP 10n
97			.BI h =u
98			Set hemisphere sampling to "uniform," meaning a single bin
99			of (cosine-distributed) samples.
100			In the case of distant "source" primitives, this is the only
101			sampling method that supports arbitrary receiver sizes.
102			The other methods below require a full hemispherical source.
103			.TP
104			.BI h =kf
105			Divide the hemisphere using the LBNL/Klems "full" sampling basis.
106			(Use "h=-kf" for left-handed coordinates.)
107			.TP
108			.BI h =kh
109			Divide the hemisphere using the LBNL/Klems "half" sampling basis.
110			(Use "h=-kh" for left-handed coordinates.)
111			.TP
112			.BI h =kq
113			Divide the hemisphere using the LBNL/Klems "quarter" sampling basis.
114			(Use "h=-kq" for left-handed coordinates.)
115			.TP
116			.BI h =rN
117			Divide the hemisphere using Reinhart's substructuring of the Tregenza
118			sky pattern with
119			.I N
120			divisions in each dimension.
121			If it is not given,
122			.I N
123			defaults to 1, which is just the Tregenza sky.
124			(Use "h=-rN" for left-handed coordinates.)
125			.TP
126			.BI h =cie
127			Divide the hemisphere into CIE sky scanner directions, which is
128			similar to Tregenza but with different starting azimuths and
129			reversing row direction at each new altitude.
130			(Use "h=-cie" for left-handed coordinates.)
131			.TP
132			.BI h =scN
133			Subdivide the hemisphere using the Shirley-Chiu square-to-disk mapping with an
134			.I NxN
135			grid over the square.
136			(Use "h=-scN" for left-handed coordinates.)
137			.TP
138			.BI u =[-]{X\|Y\|Z\|ux,uy,uz}
139			Orient the "up" direction for the hemisphere using the indicated axis or direction
140			vector.
141			.TP
142			.BI o =output_spec
143	greg	1.2	Send the matrix data for this receiver to the indicated file specification.
144			Single or double quotes may be used to contain strings with spaces, and
145			the usual "%s" and "%d" formats incorporate the modifier name and/or
146			bin number, as with
147			.I rcontrib.
148	greg	1.1	Command (piped) output is not supported.
149	greg	1.2	.PP
150			If no output_spec directive is given, it must be specified by a
151			.I \-o
152			setting on the command-line, since output to stdout is not supported.
153			The input and output file formats are controlled by the
154	greg	1.1	.I \-fio
155	greg	1.2	option, which may use a single letter for identical i/o formats.
156			The input format matters only in pass-through mode, for which
157	greg	1.1	ASCII input is supported.
158			ASCII output is unsupported, since it interferes with
159			efficient recovery in the
160			.I \-r
161			mode.
162	greg	1.2	The default setting is
163			.I \-faf.
164	greg	1.1	.PP
165			In normal execution, only a single sender surface is sampled, but it may be
166			comprised of any number of subsurfaces, as in a triangle mesh or similar.
167			The surface normal will be computed as the average of all the constituent
168			subsurfaces.
169			The subsurfaces themselves must be planar, thus only
170			.I polygon
171			and
172			.I ring
173			surface primitives are supported.
174			Other primitives will be silently ignored and will have no effect on the calculation.
175			.PP
176			In the receiver file, the
177			.I source
178			primitive is supported as well, and multiple receivers (and multiple output
179			matrices) may be identified by different modifier names.
180			(Make sure that surfaces using the same modifier are grouped together,
181			and that the modifiers are unique and not used elsewhere in the
182			scene description.)\0
183			Though it may be counter-intuitive, receivers are often light sources,
184			since samples end up there in a backwards ray-tracing system such as RADIANCE.
185			When using local geometry, the overall aperture shape should be close to flat.
186			Large displacements may give rise to errors due to a convex receiver's
187			larger profile at low angles of incidence.
188			.PP
189			Rays always emanate from the back side of the sender surface and arrive at the
190			front side of receiver surfaces.
191			In this way, a receiver surface may be reused as a sender in a subsequent
192			.I rxfluxmtx
193			calculation and the resulting matrices will concatenate properly.
194			(Note that it is important to keep receiver surfaces together, otherwise a
195			"duplicate modifier" error will result.)\0
196			.SH EXAMPLES
197			To generate a flux transfer matrix connecting input and output apertures
198			on a light pipe:
199			.IP "" .2i
200			rxfluxmtx int_aperture.rad ext_aperture.rad lpipe.rad > lpipe.mtx
201			.PP
202	greg	1.2	To generate a set of DC view component pictures with 9 jittered samples/pixel:
203	greg	1.1	.IP "" .2i
204	greg	1.2	rxfluxmtx -vf v1.vf -x 512 -y 512 -c 9 -pj .8 -fc reinhart_M4.rad -i scene1.oct
205	greg	1.1	.PP
206			To compute a workplane irradiance matrix for each window in a space:
207			.IP "" .2i
208			rxfluxmtx -faf - windows_kf.rad -i scene2.oct < workplane_pts.txt
209			.SH NOTES
210			The main differences between
211			.I rfluxmtx(1)
212			and
213			.I rxfluxmtx
214			is that the latter does not run a separate
215			.I rcontrib
216			process.
217			Instead, it relies on a unix-only C++ class definition that offers full
218			control over i/o.
219			This allows an unlimited number of receivers, a
220			.I \-r
221			recovery option, and simplifies internal operations.
222			.SH AUTHOR
223			Greg Ward
224			.SH "SEE ALSO"
225			genBSDF(1), getinfo(1), pvsum(1), rcalc(1), rcollate(1), rcomb(1), rcontrib(1),
226			rcrop(1), rfluxmtx(1), rmtxop(1), vwrays(1), wrapBSDF(1)