man/man1/bsdf2ttree.1

.\" RCSid $Id: bsdf2ttree.1,v 1.9 2020/11/13 19:21:11 greg Exp $
.TH BSDF2TTREE 1 4/24/2013 RADIANCE
.SH NAME
bsdf2ttree - generate XML tensor tree description of a BSDF
.SH SYNOPSIS
.B bsdf2ttree
[
.B "\-pC"
][
.B "{+|-}a"
][
.B "\-g Nlog2"
][
.B "\-t pctcull"
][
.B "\-n nss"
][
.B "\-s thresh"
][
.B "\-l maxlobes"
][
.B "bsdf.sir .."
]
.br
or
.br
.B bsdf2ttree
.B "\-t{3|4}"
[
.B "\-pC"
][
.B "{+|-}a"
][
.B "\-g Nlog2"
][
.B "\-t pctcull"
][
.B "\-n nss"
][
.B "\-s thresh"
][
.B "{+|-}forward"
][
.B "{+|-}backward"
][
.B "\-e expr"
][
.B "\-f file"
]
.B bsdf_func
.SH DESCRIPTION
.I Bsdf2ttree
produces a tensor tree representation of a
bidirectional scattering distribution function (BSDF)
based on an intermediate representation (in the first form) or
a functional description (in the second form).
A complete XML description is written to the standard output,
which is normally redirected to a file.
.PP
The
.I \-p
option by itself turns off the progress bar, whose length may be set
by an immediately following integer argument.
(The default progress bar length is 79 characters.)\0
.PP
The
.I \-a
option turns off reciprocity averaging for isotropic scattering or anisotropic reflection.
Normally on (+a), this ensures that the tensor BRDF obeys Helmholtz reciprocity.
However, in certain rare cases, reciprocity averaging can cause unwanted noise in the output.
.PP
The maximum resolution of the tensor tree may be controlled by the
.I \-g
option, which defaults to a value of 6.
This corresponds to a peak resolution of 2^6 (64) in each dimension.
Due to memory and time constraints, it is not recommended to set
.I \-g
higher than 7, which corresponds to a 128x128x128x128 initial sampling,
or 268 million values.
.PP
The initial sampling is pared down by the percentage specified with the
.I \-t
option, which defaults to 90.
Setting this parameter to -1 turns culling off entirely, which may be
useful for comparisons.
.PP
The
.I \-n
option controls the number of super-samples to send in patches whose
difference to its neighbors exceeds some threshold.
The default number of super-samples is 256.
The difference threshold for super-sampling is controlled by the
.I \-s
option, and defaults to 0.35.
.PP
The first invocation form takes a intermediate scattering representation
as produced by
.I pabopto2bsdf(1)
or similar, and produces a tensor tree representation with as many
components as there are independent input distributions.
Each intermediate scattering file contains one of
the four components, and if the first component
is isotropic, all components must be isotropic.
A similar rule holds for anisotropic inputs.
The
.I \-l
option may be used to specify the maximum number of lobes in any
interpolated radial basis function.
The default value is 15000, which generally keeps the interpolation tractable.
Setting the value to 0 turns off this limit.
Parameter options may be altered between input files, in case a different
resolution or culling percentage is indicated for transmission versus
reflection for example.
.PP
In the second invocation form,
.I bsdf2ttree
takes a functional specification of a BSDF.
The named function should accept 6 parameters corresponding to the
normalized incident and exiting vectors, respectively.
By convention, these vectors point away from the surface, and a positive
Z-component corresponds to the front side.
The Y-component corresponds to the "up" orientation of the surface,
as specified in the eventual scene description that references the XML
output.
If the function only takes 3 parameters, then the variables "Dx", "Dy",
and "Dz" will be assigned to the reverse of the outgoing direction at
each evaluation.
(I.e., the vector will point into the surface and
Dz will be negative on the front side.)\0
This simplifies conversion of functional BSDF specifications using the
legacy material primitives "plasfunc", "metfunc", and "transfunc".
.PP
The function is defined by one or more
.I \-e
and
.I \-f
options, and should obey both Helmholtz reciprocity and
integrate to less than 1 over each projected incident hemisphere
for energy conservation.
The variable and function definitions in each
.I \-f source
file are read and compiled from the RADIANCE library where it is found.
If the
.I \-t3
option is specified, the defined function is assumed to be isotropic.
If the
.I \-t4
option is given, the function is assumed to be anisotropic.
.PP
Similar to the
.I genBSDF(1)
command,
the
.I \+backward
option (default) specifies that rays arriving from the front side of
the surface will be tested for reflection and transmission.
If both forward and backward (front and back) distributions are needed, the
.I \+forward
option may be given.
To turn off the backward components, use the
.I \-backward
option.
Computing both incident hemispheres takes about twice as long as one, but
is recommended when rays will be impinging from either side.
.SH EXAMPLE
To take two components of an intermediate BSDF representation and create
a high-resolution tensor tree with 85% culling on transmission and 95%
culling on reflection:
.IP "" .2i
bsdf2ttree -g 7 -t 85 transmitted.sir -t 95 reflected.sir > combined.xml
.PP
To create a low-res BSDF corresponding to a one-sided,
isotropic Phong distribution:
.IP "" .2i
bsdf2ttree -g 5 -t3 -e 'phong(ix,iy,iz,ox,oy,oz) = if(iz, .1+((iz+oz)/sqrt((ix+ox)^2+(iy+oy)^2+(iz+oz)^2))^50, 0)' phong > phong.xml
.SH ENVIRONMENT
RAYPATH         the directories to check for auxiliary files.
.SH AUTHOR
Greg Ward
.SH "SEE ALSO"
bsdf2klems(1), icalc(1), genBSDF(1), pabopto2bsdf(1), pabopto2xyz(1),
pkgBSDF(1), rcontrib(1), rfluxmtx(1), wrapBSDF(1)
Revision:	1.10
Committed:	Thu Feb 25 04:48:19 2021 UTC (4 years, 2 months ago) by greg
Branch:	MAIN
Changes since 1.9:	+3 -3 lines
Log Message:	docs: added man page for pabopto2bsdf
#	User	Rev	Content
1	greg	1.10	.\" RCSid $Id: bsdf2ttree.1,v 1.9 2020/11/13 19:21:11 greg Exp $
2	greg	1.1	.TH BSDF2TTREE 1 4/24/2013 RADIANCE
3			.SH NAME
4			bsdf2ttree - generate XML tensor tree description of a BSDF
5			.SH SYNOPSIS
6			.B bsdf2ttree
7			[
8	greg	1.4	.B "\-pC"
9			][
10	greg	1.6	.B "{+\|-}a"
11			][
12	greg	1.1	.B "\-g Nlog2"
13			][
14	greg	1.3	.B "\-t pctcull"
15			][
16	greg	1.8	.B "\-n nss"
17			][
18			.B "\-s thresh"
19			][
20	greg	1.3	.B "\-l maxlobes"
21	greg	1.9	][
22	greg	1.1	.B "bsdf.sir .."
23			]
24			.br
25			or
26			.br
27			.B bsdf2ttree
28			.B "\-t{3\|4}"
29			[
30	greg	1.4	.B "\-pC"
31			][
32	greg	1.6	.B "{+\|-}a"
33			][
34	greg	1.1	.B "\-g Nlog2"
35			][
36	greg	1.3	.B "\-t pctcull"
37	greg	1.1	][
38	greg	1.8	.B "\-n nss"
39			][
40			.B "\-s thresh"
41			][
42	greg	1.1	.B "{+\|-}forward"
43			][
44			.B "{+\|-}backward"
45			][
46	greg	1.3	.B "\-e expr"
47	greg	1.1	][
48	greg	1.3	.B "\-f file"
49	greg	1.1	]
50			.B bsdf_func
51			.SH DESCRIPTION
52			.I Bsdf2ttree
53			produces a tensor tree representation of a
54			bidirectional scattering distribution function (BSDF)
55			based on an intermediate representation (in the first form) or
56			a functional description (in the second form).
57			A complete XML description is written to the standard output,
58			which is normally redirected to a file.
59			.PP
60	greg	1.4	The
61			.I \-p
62			option by itself turns off the progress bar, whose length may be set
63			by an immediately following integer argument.
64			(The default progress bar length is 79 characters.)\0
65			.PP
66	greg	1.6	The
67			.I \-a
68			option turns off reciprocity averaging for isotropic scattering or anisotropic reflection.
69			Normally on (+a), this ensures that the tensor BRDF obeys Helmholtz reciprocity.
70			However, in certain rare cases, reciprocity averaging can cause unwanted noise in the output.
71			.PP
72	greg	1.1	The maximum resolution of the tensor tree may be controlled by the
73			.I \-g
74			option, which defaults to a value of 6.
75			This corresponds to a peak resolution of 2^6 (64) in each dimension.
76			Due to memory and time constraints, it is not recommended to set
77			.I \-g
78			higher than 7, which corresponds to a 128x128x128x128 initial sampling,
79			or 268 million values.
80			.PP
81			The initial sampling is pared down by the percentage specified with the
82			.I \-t
83			option, which defaults to 90.
84			Setting this parameter to -1 turns culling off entirely, which may be
85			useful for comparisons.
86			.PP
87	greg	1.8	The
88			.I \-n
89			option controls the number of super-samples to send in patches whose
90			difference to its neighbors exceeds some threshold.
91			The default number of super-samples is 256.
92			The difference threshold for super-sampling is controlled by the
93			.I \-s
94			option, and defaults to 0.35.
95			.PP
96	greg	1.1	The first invocation form takes a intermediate scattering representation
97			as produced by
98			.I pabopto2bsdf(1)
99			or similar, and produces a tensor tree representation with as many
100			components as there are independent input distributions.
101			Each intermediate scattering file contains one of
102			the four components, and if the first component
103			is isotropic, all components must be isotropic.
104			A similar rule holds for anisotropic inputs.
105	greg	1.3	The
106			.I \-l
107			option may be used to specify the maximum number of lobes in any
108			interpolated radial basis function.
109			The default value is 15000, which generally keeps the interpolation tractable.
110			Setting the value to 0 turns off this limit.
111	greg	1.9	Parameter options may be altered between input files, in case a different
112			resolution or culling percentage is indicated for transmission versus
113			reflection for example.
114	greg	1.1	.PP
115			In the second invocation form,
116			.I bsdf2ttree
117			takes a functional specification of a BSDF.
118	greg	1.2	The named function should accept 6 parameters corresponding to the
119	greg	1.1	normalized incident and exiting vectors, respectively.
120			By convention, these vectors point away from the surface, and a positive
121			Z-component corresponds to the front side.
122			The Y-component corresponds to the "up" orientation of the surface,
123			as specified in the eventual scene description that references the XML
124			output.
125	greg	1.2	If the function only takes 3 parameters, then the variables "Dx", "Dy",
126			and "Dz" will be assigned to the reverse of the outgoing direction at
127			each evaluation.
128			(I.e., the vector will point into the surface and
129			Dz will be negative on the front side.)\0
130			This simplifies conversion of functional BSDF specifications using the
131			legacy material primitives "plasfunc", "metfunc", and "transfunc".
132	greg	1.1	.PP
133			The function is defined by one or more
134			.I \-e
135			and
136			.I \-f
137			options, and should obey both Helmholtz reciprocity and
138			integrate to less than 1 over each projected incident hemisphere
139			for energy conservation.
140	greg	1.7	The variable and function definitions in each
141			.I \-f source
142			file are read and compiled from the RADIANCE library where it is found.
143	greg	1.1	If the
144			.I \-t3
145			option is specified, the defined function is assumed to be isotropic.
146			If the
147			.I \-t4
148			option is given, the function is assumed to be anisotropic.
149			.PP
150			Similar to the
151			.I genBSDF(1)
152			command,
153			the
154			.I \+backward
155			option (default) specifies that rays arriving from the front side of
156			the surface will be tested for reflection and transmission.
157			If both forward and backward (front and back) distributions are needed, the
158			.I \+forward
159			option may be given.
160			To turn off the backward components, use the
161			.I \-backward
162			option.
163			Computing both incident hemispheres takes about twice as long as one, but
164			is recommended when rays will be impinging from either side.
165			.SH EXAMPLE
166			To take two components of an intermediate BSDF representation and create
167	greg	1.9	a high-resolution tensor tree with 85% culling on transmission and 95%
168			culling on reflection:
169	greg	1.1	.IP "" .2i
170	greg	1.9	bsdf2ttree -g 7 -t 85 transmitted.sir -t 95 reflected.sir > combined.xml
171	greg	1.1	.PP
172			To create a low-res BSDF corresponding to a one-sided,
173			isotropic Phong distribution:
174			.IP "" .2i
175			bsdf2ttree -g 5 -t3 -e 'phong(ix,iy,iz,ox,oy,oz) = if(iz, .1+((iz+oz)/sqrt((ix+ox)^2+(iy+oy)^2+(iz+oz)^2))^50, 0)' phong > phong.xml
176	greg	1.7	.SH ENVIRONMENT
177			RAYPATH the directories to check for auxiliary files.
178	greg	1.1	.SH AUTHOR
179			Greg Ward
180			.SH "SEE ALSO"
181	greg	1.10	bsdf2klems(1), icalc(1), genBSDF(1), pabopto2bsdf(1), pabopto2xyz(1),
182			pkgBSDF(1), rcontrib(1), rfluxmtx(1), wrapBSDF(1)