1projectionintro(1)            Grass User's Manual           projectionintro(1)
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Projections and spatial transformations in GRASS GIS

6   Raster map projections
7       Raster  maps  are backward projected in GRASS. This means that the user
8       has to run the raster projection command (r.proj) in the  target  loca‐
9       tion  and "pull" the map from the source location.  Both locations need
10       to have a projection defined.
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12   Raster map transformation
13       To transform an unprojected map from a XY  location  into  a  projected
14       location  (or  another  XY  location), a forward transformation is per‐
15       formed.  The unreferenced map is geocoded within  the  XY  location  by
16       defining four corner points or by seeking several ground control points
17       (i.target, i.points) and then  transformed  into  the  target  location
18       (i.rectify).  Polynomial  transformation  of 1st, 2nd and 3rd order are
19       supported.
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21       To simply translate a raster map (without stretching or rotation),  the
22       r.region command can be used.
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24   Vector map projections
25       Vector  maps  are backward projected in GRASS. This means that the user
26       has to run the vector projection command (v.proj) in the  target  loca‐
27       tion  and "pull" the map from the source location.  Both locations need
28       to have a projection defined.
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30   Vector map transformation
31       To transform an unprojected map (e.g. CAD map) into  projected  coordi‐
32       nates,  a  forward transformation is performed. The unreferenced map is
33       imported into the location with projection  and  geocoded  within  this
34       location  by  defining  four corner points or by seeking several ground
35       control points.  These points are stored into an ASCII  file  and  then
36       transformed within the same location (v.transform).
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38   See also
39                     Introduction to GRASS raster map processing
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41                     Introduction to GRASS image processing
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43                     Introduction to GRASS vector map processing
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45       full index
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49GRASS 6.2.2                                                 projectionintro(1)
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