debian man page for projectionintro

Query: projectionintro

OS: debian

Section: 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)
Related Man Pages
imageryintro(1grass) - debian
projectionintro(1grass) - debian
rasterintro(1grass) - debian
vector(1grass) - redhat
vector(1grass) - mojave
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