DESCRIPTION
v.proj allows a user to convert a vector map in a specified mapset
of a specified location (different from current) with projection of input
location to the vector map in a current mapset of current location with
projection of current location (both projections are defined by
corresponding PROJ_INFO files). The projection information is taken from the
current PROJ_INFO files, as set and viewed with
g.proj.
NOTES
If output is not specified it is set to be the same as input map
name.
If mapset is not specified, its name is assumed to be the same
as the current mapset's name.
If dbase is not specified it is assumed to be the current
database. The user only has to specify dbase if the source
location is stored in another separate GRASS database.
If smax is set to 0 the automated vertex densification is
disabled (not recommended).
v.proj supports general datum transformations, making use of the
PROJ.4 co-ordinate system translation library.
When projecting into a latlon location, east coordinates are wrapped
by the proj4 library to fit into the range -180,180. This is in most cases
appropriate, but can cause errors the input vector crosses the datum line
at 180E/W. In this case wrapping of east coordinates to -180,180 needs
to be disabled with the -w flag.
In order to preserve spatial detail, v.proj performs automated
vertex densification (as an alternative, v.split
could be used before reprojecting. Without vertex densification, depending on
the source and target CRS (Coordinate Reference System), geometries can be
substantially deformed (straight lines become curves, squares become
trapezoids, etc). The densification of linear features can help to avoid
topological errors.
EXAMPLES
v.proj in=mymap location=latlong mapset=user1
REFERENCES
- Evenden, G.I. (1990) Cartographic
projection procedures for the UNIX environment - a user's manual.
USGS Open-File Report 90-284 (OF90-284.pdf)
See also there: Interim Report and 2nd Interim Report on Release 4, Evenden 1994).
- Richards, John A. (1993), Remote Sensing Digital Image Analysis,
Springer-Verlag, Berlin, 2nd edition.
PROJ 4: Projection/datum support library.
Further reading
SEE ALSO
g.proj,
m.proj,
r.proj,
i.rectify,
r.stats,
v.sample,
v.split,
v.surf.idw,
v.surf.rst
AUTHORS
Irina Kosinovsky, US ARMY CERL
M.L. Holko, USDA, SCS, NHQ-CGIS
R.L. Glenn, USDA, SCS, NHQ-CGIS
Last changed: $Date$