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 (12 days, 7 hours ago) by greg
Branch:	MAIN
CVS Tags:	HEAD
Changes since 1.1:	+17 -8 lines
Log Message:	docs(rxfluxmtx): wording corrections and clarifications
#	Content
1	.\" RCSid "$Id: rxfluxmtx.1,v 1.1 2025/10/23 23:34:59 greg Exp $"
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 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	Command (piped) output is not supported.
149	.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	.I \-fio
155	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	ASCII input is supported.
158	ASCII output is unsupported, since it interferes with
159	efficient recovery in the
160	.I \-r
161	mode.
162	The default setting is
163	.I \-faf.
164	.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	To generate a set of DC view component pictures with 9 jittered samples/pixel:
203	.IP "" .2i
204	rxfluxmtx -vf v1.vf -x 512 -y 512 -c 9 -pj .8 -fc reinhart_M4.rad -i scene1.oct
205	.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)