[GRASS-user] Alaska shapefile crosses 180th parallel

[Brent Wood]

Paul Van Deusen wrote:

Welcome to my world :-)

Working in the maritime area around New Zealand, 180 is an issue I deal 
with regularly :-(

I suggest you add 360 to every longitude < 0. This moves the break to 
zero degrees instead of 180.

You can also use a variety of local projections to avoid the issue.

 There is a parameter in the CVS version of proj4 to set the central 
meridian, defaults to zero, but a reprojection to WGS84 (EPSG:4326) with 
explicit parameters, & the central meridian of 18- works well....

Brent Wood

> 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..
>
> Spatial_Reference_Information:
>  Horizontal_Coordinate_System_Definition:
>    Geographic:
>      Latitude_Resolution: 0.000278
>      Longitude_Resolution: 0.000278
>      Geographic_Coordinate_Units: Decimal degrees
>    Geodetic_Model:
>      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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