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databaseintro(1grass) Grass User's Manual databaseintro(1grass)

Database management in GRASS GIS
Attribute management in general
GRASS can be linked to one or many database management systems (DBMS). The db.* set of commands provides basic SQL support for attribute
management, while the v.db.* set of commands operates on the vector map (see Vector introduction).

Available drivers
Available drivers are listed in SQL support in GRASS GIS.

Notes:
The default DBF driver provides only very limited SQL support (as DBF is not an SQL DB) while the other DBMS backends (such as PostgreSQL,
MySQL etc) provide full SQL support since the SQL commands are sent directly to the DBMS.

DB connection management
The current database management settings are shown or modified with db.connect for current mapset. Available DBMI drivers are listed with
db.drivers. Some DBMI backends require a user/password for driver/database to be set with db.login. In order to test a driver, run
db.test.

Attribute data import and export
Attribute data can be imported with db.in.ogr from various formats and exported with db.out.ogr. To internally copy a a full table or
selectively parts of it, use db.copy.

Further conversion tools:

MDB Tools: Convert MS-Access data to SQL, DBF, etc.

Openoffice.org with SQL Databases

SQL commands
GRASS supports to main SQL operations, execution of an SQL statement (db.execute) and selection of data from a table (db.select). See the
SQL help page for examples.

Managing the default DBMI settings
Per default vector map attributes are stored in DBF table files. This default definition can be modified with db.connect. If an external
DBMS is used, db.login may be required.

Creating a database
Specific commands are explained on the individual driver pages (these pages are only available if driver was compiled in this installa-
tion):

DBF: see DBF page

SQLite: SQLite page

mySQL: meSQL pages

ODBC: ODBC page (connect to Oracle, etc.)

PostgreSQL: PostgreSQL and PostGIS page

Metadata
All columns for a given table are listed with db.columns. The command db.describe describes a table in detail. To list all available
tables for a given database, run db.tables.

Table maintenance
To drop a column from a selected attribute table, use db.dropcol. With db.droptable an attribute table can be deleted.

Database Schema
Currently schema support only works for PostgreSQL connections. Default schema can be set with db.connect. Note that the default schema
will be used by all db.* modules.

db.tables returns 'schema.table' if schemas are available in the database.

Migrating to a different database engine
To migrate a GRASS database table (or a GRASS vector map) to a different DBMI engine, the best solution is to create a new MAPSET, define
the DBMI settings accordingly with db.login. Then the table of interest can be copied over with db.copy from the original MAPSET. Like-
wise, a vector map including its table(s) are copied from the original MAPSET to the current MAPSET with g.copy.

See also
Introduction to GRASS vector map processing

Introduction to GRASS raster map processing
Main index - database index - full index

GRASS 6.4.2 databaseintro(1grass)

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projectionintro(1grass) 					Grass User's Manual					   projectionintro(1grass)

NAME

       projectionintro - Projections and spatial transformations

       Projections and spatial transformations

Projections and spatial transformations in GRASS GIS
   Introduction
       A  GRASS  location is referenced with a single projection and coordinate system (or unreferenced as XY location). When creating a new loca-
       tion from an existing raster or vector map using the tools available from the startup screen or the map	import	commands,  projection  and
       coordinate  system  are defined.  To change the projection of maps, a new location has to be created and the desired maps have to be repro-
       jected into it from the source location as explained below.

   Raster map projections
       Raster maps are backward projected in GRASS. This means that the user has to run the raster projection command (r.proj) in the target loca-
       tion and "pull" the map from the source location.  Both locations need to have a projection defined.

   Raster map transformation
       To  transform  an  unprojected  map from a XY location into a projected location (or another XY location), a forward transformation is per-
       formed.	The unreferenced map is geocoded within the XY location by defining four corner points or by seeking several ground control points
       (i.target,  i.points)  and  then  transformed into the target location (i.rectify). Polynomial transformation of 1st, 2nd and 3rd order are
       supported.

       A graphical user interface is provided by gis.m.

       To simply translate a raster map (without stretching or rotation), the r.region command can be used.

   Vector map projections
       Vector maps are backward projected in GRASS. This means that the user has to run the vector projection command (v.proj) in the target loca-
       tion and "pull" the map from the source location.  Both locations need to have a projection defined.

   Vector map transformation
       To  transform  an unprojected map (e.g. CAD map) into projected coordinates, a forward transformation is performed. The unreferenced map is
       imported into the location with projection and geocoded within this location by defining  four corner points or by seeking  several  ground
       control points.	These points are stored into an ASCII file and then transformed within the same location (v.transform).

       A graphical user interface is provided by gis.m.

   References
		      ASPRS Grids and Datum

		      Projections Transform List (PROJ4)

		      MapRef - The Collection of Map Projections and Reference Systems for Europe

		      Information and Service System for European Coordinate Reference Systems - CRS

   See also
		     Introduction to GRASS raster map processing

		     Introduction to GRASS image processing

		     Introduction to GRASS vector map processing

       full index

       (C) 2008-2011 GRASS Development Team

GRASS 6.4.2														   projectionintro(1grass)

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