man/man1/rxfluxmtx.1

.\" RCSid "$Id$"
.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 or command.
Single or double quotes may be used to contain strings with spaces.
Command (piped) output is not supported.
The file format will be determined by the command-line
.I \-fio
option, which may use a single letter for identical input and output formats.
The input file specification 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.
.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 samples/pixel:
.IP "" .2i
rxfluxmtx -vf v1.vf -x 512 -y 512 -c 9 -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:	1.1
Committed:	Thu Oct 23 23:34:59 2025 UTC (13 days, 13 hours ago) by greg
Branch:	MAIN
Log Message:	docs: Added rxfluxmtx man page and updated others accordingly
#	Content
1	.\" RCSid "$Id$"
2	.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	Send the matrix data for this receiver to the indicated file or command.
144	Single or double quotes may be used to contain strings with spaces.
145	Command (piped) output is not supported.
146	The file format will be determined by the command-line
147	.I \-fio
148	option, which may use a single letter for identical input and output formats.
149	The input file specification matters only in pass-through mode, for which
150	ASCII input is supported.
151	ASCII output is unsupported, since it interferes with
152	efficient recovery in the
153	.I \-r
154	mode.
155	.PP
156	In normal execution, only a single sender surface is sampled, but it may be
157	comprised of any number of subsurfaces, as in a triangle mesh or similar.
158	The surface normal will be computed as the average of all the constituent
159	subsurfaces.
160	The subsurfaces themselves must be planar, thus only
161	.I polygon
162	and
163	.I ring
164	surface primitives are supported.
165	Other primitives will be silently ignored and will have no effect on the calculation.
166	.PP
167	In the receiver file, the
168	.I source
169	primitive is supported as well, and multiple receivers (and multiple output
170	matrices) may be identified by different modifier names.
171	(Make sure that surfaces using the same modifier are grouped together,
172	and that the modifiers are unique and not used elsewhere in the
173	scene description.)\0
174	Though it may be counter-intuitive, receivers are often light sources,
175	since samples end up there in a backwards ray-tracing system such as RADIANCE.
176	When using local geometry, the overall aperture shape should be close to flat.
177	Large displacements may give rise to errors due to a convex receiver's
178	larger profile at low angles of incidence.
179	.PP
180	Rays always emanate from the back side of the sender surface and arrive at the
181	front side of receiver surfaces.
182	In this way, a receiver surface may be reused as a sender in a subsequent
183	.I rxfluxmtx
184	calculation and the resulting matrices will concatenate properly.
185	(Note that it is important to keep receiver surfaces together, otherwise a
186	"duplicate modifier" error will result.)\0
187	.SH EXAMPLES
188	To generate a flux transfer matrix connecting input and output apertures
189	on a light pipe:
190	.IP "" .2i
191	rxfluxmtx int_aperture.rad ext_aperture.rad lpipe.rad > lpipe.mtx
192	.PP
193	To generate a set of DC view component pictures with 9 samples/pixel:
194	.IP "" .2i
195	rxfluxmtx -vf v1.vf -x 512 -y 512 -c 9 -fc reinhart_M4.rad -i scene1.oct
196	.PP
197	To compute a workplane irradiance matrix for each window in a space:
198	.IP "" .2i
199	rxfluxmtx -faf - windows_kf.rad -i scene2.oct < workplane_pts.txt
200	.SH NOTES
201	The main differences between
202	.I rfluxmtx(1)
203	and
204	.I rxfluxmtx
205	is that the latter does not run a separate
206	.I rcontrib
207	process.
208	Instead, it relies on a unix-only C++ class definition that offers full
209	control over i/o.
210	This allows an unlimited number of receivers, a
211	.I \-r
212	recovery option, and simplifies internal operations.
213	.SH AUTHOR
214	Greg Ward
215	.SH "SEE ALSO"
216	genBSDF(1), getinfo(1), pvsum(1), rcalc(1), rcollate(1), rcomb(1), rcontrib(1),
217	rcrop(1), rfluxmtx(1), rmtxop(1), vwrays(1), wrapBSDF(1)