man/man1/rxfluxmtx.1

.\" RCSid "$Id: rxfluxmtx.1,v 1.3 2025/11/10 23:35:55 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 "-bj frac"
] [
.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).
Likewise, the
.I \-c
option specifies the number of times to repeat each sample.
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
.I \-bj
option sets the amount of bin jittering, which blurs the boundaries of
receiver bins and is generally recommended when creating a view that may
include direct visibility of the receiver surface(s).
It is best used in combination with the
.I \-c
and
.I \-pj
options described above.
(The default jitter is 0, leaving sharp bin boundaries.)\0
.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.
The default setting is
.I \-faf.
ASCII output is unsupported, since it interferes with
efficient recovery when using the
.I \-r
option.
.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 -o lpipe.mtx int_aperture.rad ext_aperture.rad lpipe.rad
.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 streamlines 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:	1.4
Committed:	Fri Nov 14 23:51:42 2025 UTC (2 days, 21 hours ago) by greg
Branch:	MAIN
CVS Tags:	HEAD
Changes since 1.3:	+18 -1 lines
Log Message:	feat(rfluxmtx,rxfluxmtx): Added bin sample jittering for smoother visual results
#	Content
1	.\" RCSid "$Id: rxfluxmtx.1,v 1.3 2025/11/10 23:35:55 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 "-bj frac"
11	] [
12	.B "rcontrib options"
13	]
14	.B "{ sender.rad \| view \| - }"
15	.B receivers.rad
16	.B "[ -i system.oct ]"
17	.B "[ system.rad .. ]"
18	.SH DESCRIPTION
19	.I rxfluxmtx
20	samples rays uniformly over the surface given in
21	.I sender.rad
22	and records rays arriving at surfaces in the file
23	.I receivers.rad,
24	producing a flux transfer matrix per receiver.
25	A system octree to which the receivers will be appended may be given with a
26	.I \-i
27	option following the receiver file.
28	Additional system surfaces may be given in one or more
29	.I system.rad
30	files, which are compiled before the receiver file into an octree used
31	to perform the simulation.
32	.PP
33	If a single hyphen ('-') is given in place of the view or sender file, then
34	.I rxfluxmtx
35	computes matrix rows based upon the provided ray sample origins and directions,
36	which may be surface normals if the
37	.I \-I+
38	option is applied.
39	The
40	.I \-y
41	option is required to specify the number of output rows for pass-through mode.
42	.PP
43	Alternatively, a view specification may be given on the command-line
44	to produce coefficient picture output, in which case both the
45	.I \-x
46	and
47	.I \-y
48	options must be present to set the desired picture dimensions.
49	The related
50	.I \-pj,
51	.I \-pd,
52	and
53	.I \-pa
54	options may be used to set the pixel jitter, depth-of-field, and
55	aspect ratio, respectively.
56	This avoids the need to call
57	.I vwrays(1),
58	as required by
59	.I rfluxmtx.
60	.PP
61	The
62	.I \-W+
63	option turns on verbose mode, and the
64	.I \-t
65	option sets the number of seconds between progress reports, similar to
66	.I rcontrib(1).
67	Likewise, the
68	.I \-c
69	option specifies the number of times to repeat each sample.
70	However, the
71	.I rcontrib
72	options
73	.I \-p,
74	.I \-b,
75	.I \-bn,
76	.I \-m,
77	and
78	.I \-M
79	options are controlled by
80	.I rxfluxmtx
81	and may not be set by the user.
82	.PP
83	The
84	.I \-bj
85	option sets the amount of bin jittering, which blurs the boundaries of
86	receiver bins and is generally recommended when creating a view that may
87	include direct visibility of the receiver surface(s).
88	It is best used in combination with the
89	.I \-c
90	and
91	.I \-pj
92	options described above.
93	(The default jitter is 0, leaving sharp bin boundaries.)\0
94	.PP
95	The sample count, unless set by the
96	.I \-c
97	option, defaults to 10000 when a sender file is given, or to 1 for
98	view and pass-through modes.
99	.SH VARIABLES
100	The sender and receiver scene files given to
101	.I rxfluxmtx
102	contain controlling parameters in special comments of the form:
103	.nf
104
105	#@rxfluxmtx variable=value ..
106	or:
107	#@rfluxmtx variable=value ..
108
109	.fi
110	At minimum, both sender and receiver must specify one of the
111	hemisphere sampling types, and there must be at least
112	one surface in each file.
113	.TP 10n
114	.BI h =u
115	Set hemisphere sampling to "uniform," meaning a single bin
116	of (cosine-distributed) samples.
117	In the case of distant "source" primitives, this is the only
118	sampling method that supports arbitrary receiver sizes.
119	The other methods below require a full hemispherical source.
120	.TP
121	.BI h =kf
122	Divide the hemisphere using the LBNL/Klems "full" sampling basis.
123	(Use "h=-kf" for left-handed coordinates.)
124	.TP
125	.BI h =kh
126	Divide the hemisphere using the LBNL/Klems "half" sampling basis.
127	(Use "h=-kh" for left-handed coordinates.)
128	.TP
129	.BI h =kq
130	Divide the hemisphere using the LBNL/Klems "quarter" sampling basis.
131	(Use "h=-kq" for left-handed coordinates.)
132	.TP
133	.BI h =rN
134	Divide the hemisphere using Reinhart's substructuring of the Tregenza
135	sky pattern with
136	.I N
137	divisions in each dimension.
138	If it is not given,
139	.I N
140	defaults to 1, which is just the Tregenza sky.
141	(Use "h=-rN" for left-handed coordinates.)
142	.TP
143	.BI h =cie
144	Divide the hemisphere into CIE sky scanner directions, which is
145	similar to Tregenza but with different starting azimuths and
146	reversing row direction at each new altitude.
147	(Use "h=-cie" for left-handed coordinates.)
148	.TP
149	.BI h =scN
150	Subdivide the hemisphere using the Shirley-Chiu square-to-disk mapping with an
151	.I NxN
152	grid over the square.
153	(Use "h=-scN" for left-handed coordinates.)
154	.TP
155	.BI u =[-]{X\|Y\|Z\|ux,uy,uz}
156	Orient the "up" direction for the hemisphere using the indicated axis or direction
157	vector.
158	.TP
159	.BI o =output_spec
160	Send the matrix data for this receiver to the indicated file specification.
161	Single or double quotes may be used to contain strings with spaces, and
162	the usual "%s" and "%d" formats incorporate the modifier name and/or
163	bin number, as with
164	.I rcontrib.
165	Command (piped) output is not supported.
166	.PP
167	If no output_spec directive is given, it must be specified by a
168	.I \-o
169	setting on the command-line, since output to stdout is not supported.
170	The input and output file formats are controlled by the
171	.I \-fio
172	option, which may use a single letter for identical i/o formats.
173	The input format matters only in pass-through mode, for which
174	ASCII input is supported.
175	The default setting is
176	.I \-faf.
177	ASCII output is unsupported, since it interferes with
178	efficient recovery when using the
179	.I \-r
180	option.
181	.PP
182	In normal execution, only a single sender surface is sampled, but it may be
183	comprised of any number of subsurfaces, as in a triangle mesh or similar.
184	The surface normal will be computed as the average of all the constituent
185	subsurfaces.
186	The subsurfaces themselves must be planar, thus only
187	.I polygon
188	and
189	.I ring
190	surface primitives are supported.
191	Other primitives will be silently ignored and will have no effect on the calculation.
192	.PP
193	In the receiver file, the
194	.I source
195	primitive is supported as well, and multiple receivers (and multiple output
196	matrices) may be identified by different modifier names.
197	(Make sure that surfaces using the same modifier are grouped together,
198	and that the modifiers are unique and not used elsewhere in the
199	scene description.)\0
200	Though it may be counter-intuitive, receivers are often light sources,
201	since samples end up there in a backwards ray-tracing system such as RADIANCE.
202	When using local geometry, the overall aperture shape should be close to flat.
203	Large displacements may give rise to errors due to a convex receiver's
204	larger profile at low angles of incidence.
205	.PP
206	Rays always emanate from the back side of the sender surface and arrive at the
207	front side of receiver surfaces.
208	In this way, a receiver surface may be reused as a sender in a subsequent
209	.I rxfluxmtx
210	calculation and the resulting matrices will concatenate properly.
211	(Note that it is important to keep receiver surfaces together, otherwise a
212	"duplicate modifier" error will result.)\0
213	.SH EXAMPLES
214	To generate a flux transfer matrix connecting input and output apertures
215	on a light pipe:
216	.IP "" .2i
217	rxfluxmtx -o lpipe.mtx int_aperture.rad ext_aperture.rad lpipe.rad
218	.PP
219	To generate a set of DC view component pictures with 9 jittered samples/pixel:
220	.IP "" .2i
221	rxfluxmtx -vf v1.vf -x 512 -y 512 -c 9 -pj .8 -fc reinhart_M4.rad -i scene1.oct
222	.PP
223	To compute a workplane irradiance matrix for each window in a space:
224	.IP "" .2i
225	rxfluxmtx -faf - windows_kf.rad -i scene2.oct < workplane_pts.txt
226	.SH NOTES
227	The main differences between
228	.I rfluxmtx(1)
229	and
230	.I rxfluxmtx
231	is that the latter does not run a separate
232	.I rcontrib
233	process.
234	Instead, it relies on a unix-only C++ class definition that offers full
235	control over i/o.
236	This allows an unlimited number of receivers, a
237	.I \-r
238	recovery option, and streamlines operations.
239	.SH AUTHOR
240	Greg Ward
241	.SH "SEE ALSO"
242	genBSDF(1), getinfo(1), pvsum(1), rcalc(1), rcollate(1), rcomb(1), rcontrib(1),
243	rcrop(1), rfluxmtx(1), rmtxop(1), vwrays(1), wrapBSDF(1)