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.\" RCSid "$Id$" |
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.TH RPIECE 1 5/25/05 RADIANCE |
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.TH RTCONTRIB 1 5/25/05 RADIANCE |
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.SH NAME |
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rtcontrib - compute contributions in a RADIANCE scene |
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rtcontrib - compute contribution coefficients in a RADIANCE scene |
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.SH SYNOPSIS |
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.B rtcontrib |
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[ |
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.B "\-n nprocs" |
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][ |
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.B \-V |
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][ |
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.B \-c |
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][ |
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.B \-fo |
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| |
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.B \-r |
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][ |
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.B "\-e expr" |
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][ |
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.B "\-f source" |
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][ |
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.B "\-o fspec" |
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.B "\-o ospec" |
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][ |
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.B "\-b binv" |
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][ |
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.B "\-bn nbins" |
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] |
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{ |
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.B "\-m mod | \-M file" |
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} |
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.. |
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[ |
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.B $EVAR |
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] |
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[ |
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rtrace options |
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] |
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– |
.B "\-m mod .." |
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.B octree |
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.br |
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.B "rtcontrib [ options ] \-defaults" |
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.SH DESCRIPTION |
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.I Rtcontrib |
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computes ray contributions (i.e., color coefficients) |
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computes ray coefficients |
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for objects whose modifiers are named in one or more |
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.I \-m |
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settings. |
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These modifiers are usually materials associated with specific |
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light sources, though they could correspond to intermediate objects as well. |
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The resulting contributions may then be used in linear combination to |
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These modifiers are usually materials associated with |
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light sources or sky domes, and must directly modify some geometric |
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primitives to be considered in the output. |
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A modifier list may also be read from a file using the |
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.I \-M |
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option. |
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The RAYPATH environment variable determines directories to search for |
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this file. |
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(No search takes place if a file name begins with a '.', '/' or '~' |
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character.)\0 |
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.PP |
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By setting the boolean |
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.I \-V |
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option, you may instruct |
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.I rtcontrib |
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to report the contribution from each material rather than the ray |
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coefficient. |
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This is particularly useful for light sources with directional output |
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distributions, whose value would otherwise be lost in the shuffle. |
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With the default |
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.I -V- |
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setting, the output of rtcontrib is a coefficient that must be multiplied |
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by the radiance of each material to arrive at a final contribution. |
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This is more convenient for computing daylight coefficeints, or cases |
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where the actual radiance is not desired. |
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Use the |
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.I -V+ |
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setting when you wish to simply sum together contributions |
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(with possible adjustment factors) to obtain a final radiance value. |
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Combined with the |
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.I \-i |
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or |
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.I \-I |
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option, irradiance contributions are reported by |
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.I \-V+ |
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rather than radiance, and |
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.I \-V- |
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coefficients contain an additonal factor of PI. |
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.PP |
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The output of |
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.I rtcontrib |
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has many potential uses. |
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Source contributions can be used as components in linear combination to |
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reproduce any desired variation, e.g., simulating lighting controls or |
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changing sky conditions via daylight coefficients. |
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More generally, |
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.I rtcontrib |
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can compute general input-output relationships in optical |
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systems, such as light pipes and shading devices. |
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can be used to compute arbitrary input-output relationships in optical |
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systems, such as luminaires, light pipes, and shading devices. |
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.PP |
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.I Rtrace(1) |
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is called to calculate the contributions for each input ray, |
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and the output tallies are sent to one or more files according to the |
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Setting the |
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.I \-c |
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option instructs |
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.I rtcontrib |
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to accumulate values rather than reporting one record per ray. |
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With this option, only a single record will be produced at the very |
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end, corresponding to the sum of all rays given on the input. |
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This is equivalent to passing all the output records through a program like |
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.I total(1) |
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to sum RGB values together, but is much more efficient. |
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Using this option, it is possible to reverse sampling, sending rays from |
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a parallel source such as the sun to a diffuse surface, for example. |
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Care must be taken to perform normalization based on the |
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radiation density and the number of rays sampled. |
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.PP |
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.I Rtcontrib |
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calls |
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.I rtrace(1) |
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with the \-oTW (or \-oTV) option to calculate the daughter ray |
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contributions for each input ray, and the output tallies |
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are sent to one or more destinations according to the given |
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.I \-o |
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specification. |
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If the output file specification contains a "%s" format, this will be |
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If a destination begins with an exclamation mark ('!'), then |
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a pipe is opened to a command and data is sent to its standard input. |
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Otherwise, the destination is treated as a file. |
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An existing file of the same name will not be clobbered, unless the |
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.I \-fo |
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option is given. |
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If instead the |
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.I \-r |
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option is specified, data recovery is attempted on existing files. |
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(If |
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.I \-c |
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is used together with the |
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.I \-r |
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option, existing files are read in and new ray evaluations are added |
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to the previous results, providing a convenient means for |
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progressive simulation.)\0 |
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If an output specification contains a "%s" format, this will be |
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replaced by the modifier name. |
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The |
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.I \-b |
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option may be used to further define |
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a "bin number" within each object if finer resolution is desired, and |
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will be applied to a "%d" format in the output file |
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a "bin number" within each object if finer resolution is needed, and |
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this will be applied to a "%d" format in the output file |
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specification if present. |
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(The actual bin number is computed at run time based on ray direction |
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and surface intersection, as described below.)\0 |
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The actual bin number is computed at run time based on ray direction |
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and surface intersection, as described below. |
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If the number of bins is known in advance, it should be specified with the |
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.I \-bn |
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option, and this is critical for output files containing multiple values |
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per record. |
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Since bin numbers start from 0, the bin count is always equal to |
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the last bin plus 1. |
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Set the this value to 0 if the bin count is unknown (the default). |
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The most recent |
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.I \-b |
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.I \-b, |
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.I \-bn |
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and |
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.I \-o |
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options (to the left) of each |
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options to the left of each |
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.I \-m |
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setting affect only that modifier, and the ordering |
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of other options is unimportant. |
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.PP |
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Input and output format defaults to plain text, where each ray's |
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origin and direction (6 real values) must appear together per |
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line of input, and one line of output is produced per output file |
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file per ray. |
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Alternative input and output formats may be specified using the |
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.I \-f[io] |
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option, which is explained in the |
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.I rtrace |
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man page along with the associated |
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setting affect only that modifier. |
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The ordering of other options is unimportant, except for |
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.I \-x |
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and |
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.I \-y |
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resolution settings. |
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In particular, the 'c' output setting |
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together with positive dimensions for |
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.I \-x |
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and |
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.I \-y |
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will produce an uncompressed RADIANCE picture, |
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suitable for manipulation with |
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.I pcomb(1) |
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and related tools. |
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if the |
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.I \-c |
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is present, when they control the resolution string |
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produced in the corresponding output. |
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.PP |
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If a |
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.I \-b |
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expression is defined for a particular modifier, |
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the bin number will be evaluated at run time for each |
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ray contribution from |
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.I rtrace. |
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Specifically, each ray's world intersection point will be assigned to |
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the variables Px, Py, and Pz, and the normalized ray direction |
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will be assigned to Dx, Dy, and Dz. |
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These parameters may be combined with definitions given in |
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.I \-e |
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arguments and files read using the |
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.I \-f |
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option. |
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The computed bin value will be |
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rounded to the nearest whole number. |
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This mechanism allows the user to define precise regions or directions |
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they wish to accumulate, such as the Tregenza sky discretization, |
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which would be otherwise impossible to specify |
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as a set of RADIANCE primitives. |
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The rules and predefined functions available for these expressions are |
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described in the |
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.I rcalc(1) |
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man page. |
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Unlike |
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.I rcalc, |
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.I rtcontrib |
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will search the RADIANCE library directories for each file given in a |
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.I \-f |
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option. |
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.PP |
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If no |
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.I \-o |
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specification is given, results are written on the standard output in order |
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of modifier (as given on the command line) then bin number. |
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The same format is used for a simple file name specification |
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without any embedded "%s" or "%d" formats. |
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Concatenated data is also sent to a single destination (i.e., an initial |
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.I \-o |
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specification without formatting strings). |
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If a "%s" format appears but no "%d" in the |
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.I \-o |
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specification, then each modifier will have its own output file, with |
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For binary output formats, there is no such delimiter to mark |
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the end of each record. |
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.PP |
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If a |
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.I \-b |
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expression is defined for a particular modifier, |
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the bin number will be evaluated at run time for each |
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ray contribution from |
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.I rtrace. |
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Specifically, each ray's world intersection point will be assigned to |
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the variables Px, Py, and Pz, and the normalized ray direction |
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will be assigned to Dx, Dy, and Dz. |
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These ray parameters may be combined with any definitions given in |
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.I \-e |
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options, or any files read in from |
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.I \-f |
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options, to compute the bin, which will be |
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rounded to the closest whole number. |
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This mechanism allows the user to define precise regions (or directions) |
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they wish to accumulate, such as the Tregenza sky grid, which would be |
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otherwise impossible to specify as a set of RADIANCE primitives. |
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Input and output format defaults to plain text, where each ray's |
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origin and direction (6 real values) are given on input, |
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and one line is produced per output file per ray. |
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Alternative data representations may be specified by the |
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.I \-f[io] |
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option, which is described in the |
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.I rtrace |
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man page along with the associated |
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.I \-x |
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and |
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.I \-y |
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resolution settings. |
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In particular, the color ('c') output data representation |
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together with positive dimensions for |
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.I \-x |
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and |
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.I \-y |
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will produce an uncompressed RADIANCE picture, |
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> |
suitable for manipulation with |
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.I pcomb(1) |
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and related tools. |
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.PP |
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If the |
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.I \-n |
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option is specified with a value greater than 1, multiple |
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.I rtrace(1) |
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.I rtrace |
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processes will be used to accelerate computation on a shared |
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memory machine. |
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Note that there is no benefit to using more processes |
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than there are local CPUs available to do the work. |
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than there are local CPUs available to do the work, and the |
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.I rtcontrib |
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process itself may use a considerable amount of CPU time. |
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.PP |
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Options may be given on the command line and/or read from the |
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environment and/or read from a file. |
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replaced by the contents of the given environment variable. |
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A command argument beginning with an at sign ('@') is immediately |
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replaced by the contents of the given file. |
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.SH EXAMPLE |
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First |
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.I rpiece |
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process is started on the machine "goober": |
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.SH EXAMPLES |
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To compute the proportional contributions from sources modified |
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by "light1" vs. "light2" on a set of illuminance values: |
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.IP "" .2i |
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goober% echo 1 8 > syncfile |
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.br |
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goober% echo -F syncfile -x 1024 -y 1024 -vf view -o picture octree > args |
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.br |
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goober% rpiece @args & |
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rtcontrib \-I+ @render.opt \-o c_%s.dat \-m light1 \-m light2 scene.oct < test.dat |
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.PP |
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Second |
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.I rpiece |
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processes is started on the machine "sucker": |
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To generate a pair of images corresponding to these two lights' |
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contributions: |
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.IP "" .2i |
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sucker% rpiece @args & |
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.SH NOTES |
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Due to NFS file buffering, the network lock manager is employed to |
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guarantee consistency in the output file even though non-overlapping |
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writes are used. |
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This would tend to slow the process down if |
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.I rpiece |
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were to wait for this I/O to complete before starting on the next |
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piece, so |
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.I rpiece |
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forks separate processes to hang around waiting for I/O completion. |
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The number of processes thus designated is set by the MAXFORK macro |
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in the program (compiled in the src/util directory). |
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If the fork call is slow on a system, it may actually be better to |
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set MAXFORK to zero. |
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In other cases, the network lock manager may be so slow that this |
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value should be increased to get the best utilization. |
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vwrays \-ff \-x 1024 \-y 1024 \-vf best.vf | |
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rtcontrib \-ffc `vwrays \-d \-x 1024 \-y 1024 \-vf best.vf` |
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@render.opt \-o c_%s.pic \-m light1 \-m light2 scene.oct |
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.PP |
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The output picture is not run-length encoded, and can be quite |
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large. |
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The approximate size (in kilobytes) can be computed by the simple |
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formula: |
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These images may then be recombined using the desired outputs |
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of light1 and light2: |
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.IP "" .2i |
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filesize = xres*yres/256 |
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pcomb \-c 100 90 75 c_light1.pic \-c 50 55 57 c_light2.pic > combined.pic |
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.PP |
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Make sure that there is enough space on the filesystem to hold the |
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entire picture before beginning. |
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Once the picture is finished, the |
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.I ra_rgbe(1) |
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program with the -r option may be used to convert to a run-length |
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encoded picture for more efficient storage, although |
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.I pfilt(1) |
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or any of the other Radiance picture filters will do the same |
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thing. |
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.PP |
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The ALRM signal may be used to gracefully terminate an |
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.I rpiece |
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process after it finishes the current piece. |
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This permits other currently running or subsequently started |
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.I rpiece |
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process(es) to continue rendering the picture without loss. |
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The |
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.I \-T |
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option will send the ALRM signal to |
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.I rpiece |
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after the specified number of (decimal) hours. |
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This is the best way to force a time limit on the computation, |
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since information will not be lost, though the process may continue |
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for some time afterwards to finish its current piece. |
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.SH BUGS |
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This program may not work on some systems whose NFS lock manager is |
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unreliable. |
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In particular, some System V derivative UNIX systems often have |
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problems with the network lock manager. |
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If the output is scrambled or rpict aborts with some ambient file |
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related problem, you should just remove the ambient file and go |
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back to normal rendering. |
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To compute an array of illuminance contributions according to a Tregenza sky: |
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.IP "" .2i |
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rtcontrib \-I+ \-b tbin \-o sky.dat \-m skyglow \-b 0 \-o ground.dat \-m groundglow |
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@render.opt \-f tregenza.cal scene.oct < test.dat |
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.SH ENVIRONMENT |
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RAYPATH path to search for \-f and \-M files |
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.SH AUTHOR |
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Greg Ward |
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.SH "SEE ALSO" |
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cnt(1), getinfo(1), pcomb(1), pfilt(1), ra_rgbe(1), |
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rcalc(1), rpict(1), rtrace(1), vwrays(1), ximage(1) |
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rcalc(1), rpict(1), rtrace(1), total(1), vwrays(1), ximage(1) |
