man/man1/bsdf2ttree.1

.\" RCSid $Id: bsdf2ttree.1,v 1.2 2013/08/02 20:56:19 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 "\-g Nlog2"
][
.B "\-t pctcull"
][
.B "\-l maxlobes"
]
[
.B "bsdf.sir .."
]
.br
or
.br
.B bsdf2ttree
.B "\-t{3|4}"
[
.B "\-g Nlog2"
][
.B "\-t pctcull"
][
.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 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 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.
.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.
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:
.IP "" .2i
bsdf2ttree -g 7 -t 85 transmitted.sir 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 AUTHOR
Greg Ward
.SH "SEE ALSO"
bsdf2klems(1), icalc(1), genBSDF(1), pkgBSDF(1)
Revision:	1.3
Committed:	Thu Sep 26 17:05:00 2013 UTC (11 years, 7 months ago) by greg
Branch:	MAIN
Changes since 1.2:	+13 -5 lines
Log Message:	Added -l option to limit maximum number of RBF lobes for interpolation
#	User	Rev	Content
1	greg	1.3	.\" RCSid $Id: bsdf2ttree.1,v 1.2 2013/08/02 20:56:19 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			.B "\-g Nlog2"
9			][
10	greg	1.3	.B "\-t pctcull"
11			][
12			.B "\-l maxlobes"
13	greg	1.1	]
14			[
15			.B "bsdf.sir .."
16			]
17			.br
18			or
19			.br
20			.B bsdf2ttree
21			.B "\-t{3\|4}"
22			[
23			.B "\-g Nlog2"
24			][
25	greg	1.3	.B "\-t pctcull"
26	greg	1.1	][
27			.B "{+\|-}forward"
28			][
29			.B "{+\|-}backward"
30			][
31	greg	1.3	.B "\-e expr"
32	greg	1.1	][
33	greg	1.3	.B "\-f file"
34	greg	1.1	]
35			.B bsdf_func
36			.SH DESCRIPTION
37			.I Bsdf2ttree
38			produces a tensor tree representation of a
39			bidirectional scattering distribution function (BSDF)
40			based on an intermediate representation (in the first form) or
41			a functional description (in the second form).
42			A complete XML description is written to the standard output,
43			which is normally redirected to a file.
44			.PP
45			The maximum resolution of the tensor tree may be controlled by the
46			.I \-g
47			option, which defaults to a value of 6.
48			This corresponds to a peak resolution of 2^6 (64) in each dimension.
49			Due to memory and time constraints, it is not recommended to set
50			.I \-g
51			higher than 7, which corresponds to a 128x128x128x128 initial sampling,
52			or 268 million values.
53			.PP
54			The initial sampling is pared down by the percentage specified with the
55			.I \-t
56			option, which defaults to 90.
57			Setting this parameter to -1 turns culling off entirely, which may be
58			useful for comparisons.
59			.PP
60			The first invocation form takes a intermediate scattering representation
61			as produced by
62			.I pabopto2bsdf(1)
63			or similar, and produces a tensor tree representation with as many
64			components as there are independent input distributions.
65			Each intermediate scattering file contains one of
66			the four components, and if the first component
67			is isotropic, all components must be isotropic.
68			A similar rule holds for anisotropic inputs.
69	greg	1.3	The
70			.I \-l
71			option may be used to specify the maximum number of lobes in any
72			interpolated radial basis function.
73			The default value is 15000, which generally keeps the interpolation tractable.
74			Setting the value to 0 turns off this limit.
75	greg	1.1	.PP
76			In the second invocation form,
77			.I bsdf2ttree
78			takes a functional specification of a BSDF.
79	greg	1.2	The named function should accept 6 parameters corresponding to the
80	greg	1.1	normalized incident and exiting vectors, respectively.
81			By convention, these vectors point away from the surface, and a positive
82			Z-component corresponds to the front side.
83			The Y-component corresponds to the "up" orientation of the surface,
84			as specified in the eventual scene description that references the XML
85			output.
86	greg	1.2	If the function only takes 3 parameters, then the variables "Dx", "Dy",
87			and "Dz" will be assigned to the reverse of the outgoing direction at
88			each evaluation.
89			(I.e., the vector will point into the surface and
90			Dz will be negative on the front side.)\0
91			This simplifies conversion of functional BSDF specifications using the
92			legacy material primitives "plasfunc", "metfunc", and "transfunc".
93	greg	1.1	.PP
94			The function is defined by one or more
95			.I \-e
96			and
97			.I \-f
98			options, and should obey both Helmholtz reciprocity and
99			integrate to less than 1 over each projected incident hemisphere
100			for energy conservation.
101			If the
102			.I \-t3
103			option is specified, the defined function is assumed to be isotropic.
104			If the
105			.I \-t4
106			option is given, the function is assumed to be anisotropic.
107			.PP
108			Similar to the
109			.I genBSDF(1)
110			command,
111			the
112			.I \+backward
113			option (default) specifies that rays arriving from the front side of
114			the surface will be tested for reflection and transmission.
115			If both forward and backward (front and back) distributions are needed, the
116			.I \+forward
117			option may be given.
118			To turn off the backward components, use the
119			.I \-backward
120			option.
121			Computing both incident hemispheres takes about twice as long as one, but
122			is recommended when rays will be impinging from either side.
123			.SH EXAMPLE
124			To take two components of an intermediate BSDF representation and create
125			a high-resolution tensor tree with 85% culling:
126			.IP "" .2i
127			bsdf2ttree -g 7 -t 85 transmitted.sir reflected.sir > combined.xml
128			.PP
129			To create a low-res BSDF corresponding to a one-sided,
130			isotropic Phong distribution:
131			.IP "" .2i
132			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
133			.SH AUTHOR
134			Greg Ward
135			.SH "SEE ALSO"
136			bsdf2klems(1), icalc(1), genBSDF(1), pkgBSDF(1)