v.projgrass - Online in the Cloud

PROGRAM:

NAME

v.proj - Re-projects a vector map from one location to the current location.

KEYWORDS

vector, projection, transformation

SYNOPSIS

v.proj
v.proj --help
v.proj [-lzw] location=name [mapset=name] [input=name] [dbase=path] [smax=float]
[output=name] [--overwrite] [--help] [--verbose] [--quiet] [--ui]

Flags:
-l
List vector maps in input mapset and exit

-z
Assume z coordinate is ellipsoidal height and transform if possible
3D vector maps only

-w
Disable wrapping to -180,180 for latlon output
Latlon output only, default is -180,180

--overwrite
Allow output files to overwrite existing files

--help
Print usage summary

--verbose
Verbose module output

--quiet
Quiet module output

--ui
Force launching GUI dialog

Parameters:
location=name [required]
Location containing input vector map
Location name (not location path)

mapset=name
Mapset containing input vector map
Default: name of current mapset

input=name
Name of input vector map to re-project

dbase=path
Path to GRASS database of input location
Default: path to the current GRASS GIS database

smax=float
Maximum segment length in meters in output vector map
Increases accuracy of reprojected shapes, disable with smax=0
Default: 10000

output=name
Name for output vector map (default: input)

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.

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, it is recommended to densify linear features with
v.split before reprojecting. Depending on the source and target CRS (Coordinate Reference
System), geometries can be substantially deformed (straight lines become curves, squares
become trapezoids, etc). In these cases densification of linear features can help to
avoid topological errors.

EXAMPLES

v.proj in=mymap location=latlong mapset=user1

REFERENCES

1 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).

2 Richards, John A. (1993), Remote Sensing Digital Image Analysis, Springer-Verlag,
Berlin, 2nd edition.

PROJ 4: Projection/datum support library.

Further reading

· ASPRS Grids and Datum

· Projections Transform List (PROJ.4)

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

· Information and Service System for European Coordinate Reference Systems - CRS

· Cartographical Map Projections by Carlos A. Furuti

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