Geografic-Information-System/grasslib.dox

/*! \mainpage GRASS GIS 8 Programmer's Manual
<!-- * doxygenized from "GRASS 5 Programmer's Manual"
       by M. Neteler 2/2004
     * updated 8/2005, 2006-2008, 2010-2011, 2017-2022
  -->

<a href="https://grass.osgeo.org">GRASS GIS</a> (<b>Geographic
Resources Analysis Support System</b>) is an open source, free
software <em>Geographical Information System</em> (GIS) with raster,
topological %vector, image processing, and graphics production
functionality that operates on various platforms through a graphical
user interface (GUI) or command line interface (CLI). It is released
under <a href="http://www.fsf.org/copyleft/gpl.html">GNU General
Public License</a> (GPL).

This manual introduces the reader to the <i>Geographic Resources
Analysis Support System</i> from the programming perspective. Design
theory, system support libraries, system maintenance, and system
enhancement are all presented. This work is part of ongoing research
being performed by the <a
href="https://grasswiki.osgeo.org/wiki/Team">GRASS Development
Team</a>, an international team of programmers, GRASS module authors
are cited within their module's source code and the contributed manual
pages.

&copy; 2000-2022 by the GRASS Development Team

This manual is published under <a
href="http://www.fsf.org/copyleft/fdl.html">GNU Free Documentation
License</a> (GFDL), and comes with ABSOLUTELY NO WARRANTY. The
development of GRASS software and this manual is kindly supported by
the <a href="https://www.osgeo.org">Open Source Geospatial
Foundation</a>, who provides the GRASS main infrastructure.

Main web site: <a
href="https://grass.osgeo.org">https://grass.osgeo.org</a>

<i>Note: Missing entries below still need to be documented in Doxygen format.</i>

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  original:
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\image html "grass8_arch.png" "GRASS GIS 8 Architecture"

\section libsOverview Libraries

\section corelibs Core libraries

(the name refers to the directory name in <tt>lib/</tt> in the source code)

 - gis: \ref gislib
 - raster: \ref rasterlib
 - vector: \ref vectorlib
 - Temporal GIS API: See https://grass.osgeo.org/grass-devel/manuals/libpython/temporal_framework.html

\section libs Further libraries

(the name refers to the directory name in <tt>lib/</tt> in the source code)

\subsection displaylibs Display Libraries and Drivers

 - display:	\ref displaylib (general display library)
 - cairodriver: \ref cairodriver
 - %driver:     Graphics monitor driver
 - htmldriver:  \ref htmldriverlib (HTML graphics driver)
 - pngdriver:   \ref pngdriverlib
 - psdriver:    \ref psdriverlib

\subsection statslibs Math and Statistics Libraries

 - arraystats:  \ref arraystatslib (library of statistics for arrays of doubles)
 - cdhc:	\ref cdhclib
 - gmath: 	\ref gmathlib (generic mathematical functions and BLAS/LAPACK library wrapper)
 - gpde:        \ref gpdelib

\subsection rasteribs Raster Libraries

 - raster:	\ref rasterlib (2D raster library)
 - raster3d:	\ref raster3dlib (3D raster aka voxels or volumes)
 - rowio:	\ref rowiolib (library for reading/writing raster rows)
 - rst:	        \ref rstlib (library for interpolation with regularized splines with tension)
 - segment:	\ref segmentlib (segment library for segmented raster reading)
 - stats:       \ref statslib (statistics library)

\subsection imagerylibs Imagery Libraries (image processing)

 - cluster:     \ref clusterlib (library for k-means style of cluster analysis processing)
 - imagery:	\ref imagerylib (library for image processing)

\subsection vectoribs Vector Libraries

 - %vector: \ref vectorlib (architecture description)
  - dglib:  \ref dglib
  - vedit:  \ref veditlib (vector editing library)
  - neta:   \ref netalib
  - rtree:  \ref rtree.h (R search tree library)

\subsection treelibs Search tree libraries

 - btree: \ref btree.h
 - btree2: \ref btree2
 - rtree:  \ref rtree.h (R search tree library)

\subsection dblibs Database Management Libraries

 - db:		\ref dbmilib

\subsection ogsflibs OpenGL Libraries and friends

 - ogsf:	\ref ogsflib (OpenGL (R) ported gsurf library (required for NVIZ))
 - nviz:        \ref nvizlib (used by wxGUI Nviz extension and CLI-based Nviz module)

\subsection pythonlibs Python API

 - python:	See GRASS GIS Python library (https://grass.osgeo.org/grass-devel/manuals/libpython/)

\subsection projlibs Projection Libraries

 - proj:	\ref projlib (wrapper to PROJ4 projection library)

\subsection misclibs Miscellaneous Libraries

 - datetime:	\ref datetime (DateTime library) 
 - external:	\ref external (External libraries from other projects such as shapelib and \ref ccmathlib)
 - fonts:	\ref fonts (GRASS fonts library)
 - init:	\ref init (GRASS initialization code + scripts)
 - iostream:	\ref iostream (fast I/O library)
 - lidar:	\ref lidar.h (LiDAR data related library)
 - linkm:	\ref linkm (linked list memory manager)
 - manage:      \ref managelib
 - symbol:	\ref symbol (Drawing symbols for %point %vector data library)

\section location File structure of GRASS Location

A GRASS <b>raster map</b> consists of several files in several subdirectories in a mapset,
organized as follows:
<dl>
 <dt><b>cellhd/</b></dt>
 <dd>map header including projection code, coordinates representing
  the spatial extent of the raster map, number of rows and columns, resolution, 
  and information about map compression;</dd>
 <dt><b>cell/, fcell/ or grid3/</b></dt>
 <dd>generic matrix of values in a compressed, portable
  format which depends on the raster data type (integer, floating %point or 3D grid);</dd>
 <dt><b>hist/</b></dt>
 <dd>history file which contains metadata such as the data source,
  the command that was used to generate the raster map, or
  other information provided by the user;</dd>
 <dt><b>cats/</b></dt>
 <dd>optional category file which contains text or numeric labels assigned
  to the raster map categories;</dd>
 <dt><b>colr/</b></dt> 
 <dd>optional color table;</dd>
 <dt><b>cell_misc/</b></dt>
 <dd>optional timestamp, range of values, quantization rules (for floating %point maps)
  and null (no-data) files;</dd>
</dl>

A GRASS <b>%vector maps</b> are stored in several separate files in a
single directory (see \ref vectorlib). While the
attributes are stored in either a DBF file, a SQLite file or in an
external DBMS (PostgreSQL, MySQL, ODBC), the geometric data are saved
as follows:

<dl>
 <dt><b>head</b></dt>
 <dd>%vector map ASCII header with information about the map creation
  (date and name), its scale and threshold;</dd>
 <dt><b>coor</b></dt>
 <dd>binary geometry file which includes the coordinates of graphic
  elements (primitives) that define the %vector feature;</dd>
 <dt><b>topo</b></dt>
 <dd>binary topology file describes the spatial relationships between the
  map's graphic elements;</dd>
 <dt><b>hist</b></dt>
 <dd>history ASCII file with complete commands that were used to
  create the %vector map, as well as the name and date/time of the map
  creation;</dd>
 <dt><b>cidx</b></dt>
 <dd>binary category index file which is used to %link the %vector
  object IDs to the attribute table rows;</dd>
 <dt><b>dbln</b></dt>
 <dd>ASCII file which contains definition(s) of %link to attribute
  storage in database (DBMS).</dd>
</dl>

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\image html "loc_struct.png" "Diagram of GRASS file structure"

\section Compiling_and_Installing_GRASS_Modules Compiling and Installing GRASS Modules

GRASS modules are compiled and installed using the UNIX <tt>make</tt>
command, which reads a file named <tt>Makefile</tt> (see \ref
Multiple_Architecture_Conventions for more information) and then runs
the compiler. The GRASS compilation process allows for
multiple-architecture compilation from a single copy of the source
code (for instance, if the source code is NFS mounted to various
machines with differing architectures). This chapter assumes that the
programmer is familiar with <tt>make</tt> and its accompanying
Makefile.
<!--
\todo Explain ''auto-conf''

\todo Include contents of SUBMITTING and INSTALL files from source code
-->
To compile enter following:

\verbatim
./configure
make
make install
\endverbatim

Then the code will be compiled into "/usr/local/grass-7.x.y" directory. The start
script "grass7x" will be placed into "/usr/local/bin/".

Optionally other target directories can be specified while "configuring":

\verbatim
./configure --prefix=/opt/grass-7.x.y --with-bindir=/usr/bin
make
make install
\endverbatim

This will store the GRASS binaries into the directory
"/opt/grass-7.x.y" and the script mentioned above into "/usr/bin".

The script "make" is required to compile single modules. The
compilation process and requirements are discussed in more detail now.

\subsection Makefile_Variables Makefile Variables

\todo Update the list.

<b>GRASS Libraries</b>. The following variables name the various GRASS 
libraries:

 - <i>GISLIB</i> - This names the <b>GIS Library</b>, which is the
principal GRASS library. See \ref gislib for details about this
library, and \ref Loading_the_GIS_Library for a sample Makefile which
loads this library.

 - <i>SEGMENTLIB</i> - This names the <b>Segment Library</b>, which
manages large matrix data. See \ref segmentlib for details about this
library, and \ref Loading_the_Segment_Library for a sample
<i>Makefile</i> which loads this library.

 - <i>RASTERLIB</i> - This names the <b>Raster Library</b>, which is
the principal GRASS library for raster data access. See \ref rasterlib
for details about this library, and \ref Loading_the_Raster_Library
for a sample <i>Makefile</i> which loads this library.

 - <i>VECTORLIB</i> - This names the <b>Vector Library</b>, which is
the principal GRASS library for vector data access. See \ref vectorlib
for details about this library, and \ref Loading_the_Vector_Library
for a sample <i>Makefile</i> which loads this library.

 - <i>DISPLAYLIB</i> - This names the <b>Display Library</b>, which
communicates with GRASS graphics drivers. See \ref displaylib for
details about this library, and \ref
Loading_the_Display_Library for a sample <i>Makefile</i>
which loads this library.

<b>UNIX Libraries:</b> The following variables name some useful UNIX 
system libraries:

 - <i>MATHLIB</i> - This names the math library. It should be used
instead of the -lm loader option.

<b>Compiler and loader variables.</b> The following variables are
related to compiling and loading C programs:

 - <i>EXTRA\_CFLAGS</i> - This variable can be used to add additional
options to <tt>$CFLAGS</tt>. It has no predefined values. It is
usually used to specify additional -I include directories, or -D
preprocessor defines.

\subsection Constructing_a_Makefile Constructing a Makefile

The complete syntax for a <i>Makefile</i> is discussed in the UNIX
documentation for <tt>make</tt> and will not be repeated here. The
essential idea is that a target (e.g. a GRASS module) is to be built
from a list of dependencies (e.g. object files, libraries, etc.). The
relationship between the target, its dependencies, and the rules for
constructing the target is expressed according to the following
syntax:

\code
target: dependencies

actions

more actions
\endcode

If the target does not exist, or if any of the dependencies have a
newer date than the target (i.e., have changed), the actions will be
executed to build the target. The actions must be indented using a
TAB. <tt>make</tt> is picky about this. It does not like spaces in
place of the TAB.

\section Multiple_Architecture_Conventions Multiple-Architecture Conventions

The following conventions allow for multiple architecture compilation
on a machine that uses a common or networked GRASS source code
directory tree.

Object files and library archives are compiled into subdirectories
that represent the architecture that they were compiled on. These
subdirectories are created in the $SRC directory as OBJ.<tt>arch</tt>
and LIB.<tt>arch</tt>, where <tt>arch</tt> represents the architecture
of the compiling machine. Thus, for example, $SRC/OBJ.sun4 would
contain the object files for Sun/4 and SPARC architectures, and
<tt>$SRC/LIB.686-pc-linux-gnu</tt> would contain library archives for
Linux architectures. Likewise, <tt>$SRC/OBJ.686-pc-linux-gnu</tt>
would contain the object files for Linux architectures, and
<tt>$SRC/LIB.686-pc-linux-gnu</tt> would contain library archives for
Linux architectures.

Note that 'arch' is defined for a specific architecture during setup
and compilation of GRASS, it is not limited to sun4 or any specific
string.

\section vectmodules Vector modules and their parameters/flags

A module is a GRASS command invoked by the user.

\subsection vectmodules_oper Modules operation

Each module which modifies and writes data must read from <b>input</b>
and write to <b>output</b> so that data may not be lost. For example
<tt>v.spag</tt> works on <b>map</b> at in GRASS GIS 5.0 but if program
(system) crashes or threshold was specified incorrectly and vector was
not backuped, data were lost. In this case <b>map</b> option should
be replaced by <b>input</b> and <b>output</b>.

Topology is always built by default if the coor file was modified.

Dimensionality is generally kept. Input 2D vector is written as 2D, 3D
as 3D. There are a few modules which change the dimension on purpose.

\subsection vectmodulesopt Modules parameters/flags

Flags:

 - <b>-b</b> do not build topo file; by default topo file is written

 - <b>-t</b> create new table, default

 - <b>-u</b> don't create new table

 - <b>-z</b> write 3D vector map (if input was 2D)

Parameters:

 - <b>map</b> input vector map for modules without output

 - <b>input</b> input vector map

 - <b>output</b> output vector map

 - <b>type</b> type of elements: point,line,boundary,centroid,area

 - <b>cat</b> category or category list (example: 1,5,9-13,35)

 - <b>layer</b> layer number or name

 - <b>where</b> condition of SQL statement for selection of records

 - <b>column</b> column name (in external table)

*/