Commit ba2a3011 authored by Ludovic Courtès's avatar Ludovic Courtès

doc: Add "Data Formats" section.

parent 7fc3a00d
\page dataformats Data File Formats
ALTA usually takes as input material reflectance measurements. While
ALTA plug-ins can support arbitrary file formats, ALTA has built-in
support for two input file formats. The first one is a simple
human-readable textual format, and the second one is a compact binary
format. This section describes the actual data formats.
Files in either format must start with a header that provides the
necessary meta-data; lines preceding this header are discarded. The
header looks like this:
#DIM 1 1
Lines starting with <tt>#</tt> are considered comments, except for those
lines that start with <tt>#</tt> immediately followed by a letter: these
constitute the <em>file header</em>.
The header ends when either a non-comment line is read, or when the
following line is encountered:
The file header essentially defines key/value associations. For
example, ALTA expects <tt>DIM</tt> key to be associated with a pair of
integers representing the dimensions of the inputs; the value for
<tt>PARAM_IN</tt> must be a string denoting a valid input
parametrization, such as <tt>RUSIN_TH_TD_PD</tt>.
Textual Data Format
For a text data file with <em>n</em> data entries where the input domain
has <em>N</em> dimensions and a <em>input_param</em> parametrization and
the output domain has <em>P</em> dimensions and a <em>output_param</em>
parametrization, the textual file format is the following:
#PARAM_IN %input_param%
#PARAM_OUT %output_param%
#VS [0|1|2] (P times)
x_{1,1} ... x_{1,N} y_{1,1} ... y_{1,P}
x_{i,1} ... x_{i,N} y_{i,1} ... y_{i,P}
x_{n,1} ... x_{n,N} y_{n,1} ... y_{n,P}
Vertical segments are not defined if VS is 0. For a VS of 1, each
sample as a radius associated for the associated dimension. If VS is 2,
each sample has a min and max segment value for the associated
Binary Data Format
In addition to the default textual format described above, ALTA supports
a compact binary format for representing raw data. The binary format
starts with a similar header:
#DIM 1 1
#FORMAT binary
#PRECISION ieee754-double
#ENDIAN little
After <tt>#BEGIN_STREAM</tt> comes a byte sequence representing the
actual data. In this example, the byte sequence is an array of 151
little-endian IEEE-754 double precision numbers. The byte sequence is
followed by <tt>#END_STREAM</tt> on a line on its own.
The header represents a matrix of <tt>SAMPLE_COUNT</tt> rows and
<tt>DIM_X + DIM_Y</tt> columns of double-precision floating point
This simple binary format was designed with two goals in mind: providing
a compact way to store large input data, and allowing implementations to
directly map the file in memory, as opposed to having to allocate
storage and parse large sequences of numbers.
...@@ -17,6 +17,10 @@ ALTA permits to manipulate various type of files. Here, we detail: our internal ...@@ -17,6 +17,10 @@ ALTA permits to manipulate various type of files. Here, we detail: our internal
+ \ref format "Function file format" + \ref format "Function file format"
+ \ref format "XML scripting format" + \ref format "XML scripting format"
#### Data formats
The \ref data-formats "Data Formats" section describes the data formats
ALTA uses to store data.
#### BRDF Related Documents #### BRDF Related Documents
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