[GRASS-user] Alaska shapefile crosses 180th parallel
b.wood at niwa.co.nz
Wed Feb 21 16:36:39 EST 2007
Paul Van Deusen wrote:
> I'm trying to read in the state boundary shapefile from
> http://nationalatlas.gov. However, the Aleutian Islands
> cross the 180th parrallel, so longitude goes from +180 to -180 at that
> point. I end up with the end of the
> Aleutian Islands getting disconnected. What is the solution? I used
> v.in.ogr and set up a location using the information that came
> with the shapefile. See spatial information below.
Welcome to my world! (oceanic GIS around New Zealand :-)
Reproject to a non lat/long coordinate system, or convert the longitudes
to a 0-360 space instead.
If you use PostGIS, shp2pgsql the shapefile, then run a query to
translate all features with a component with long<0 by 360 on the X
axis, then add these back to your original dataset, then pgsql2shp this
to a new shapefile.
It works for me :-)
FYI, I'm submitting a request to EPSG to have 2 lat/long projections, so
as well as EPSG:4326 which defaults to +-180, we have an EPSG code for
the same projection with a 0-360 long space. I don't know how they'll
feel about it, but we'll see...
> Latitude_Resolution: 0.000278
> Longitude_Resolution: 0.000278
> Geographic_Coordinate_Units: Decimal degrees
> Horizontal_Datum_Name: North American Datum of 1983
> Ellipsoid_Name: GRS1980
> Semi-major_Axis: 6378137
> Denominator_of_Flattening_Ratio: 298.257222
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