[GRASS-user] Alaska shapefile crosses 180th parallel

[Gary Sherman]

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If you are only interested in Alaska an perhaps part of Canada and  
Russia, you could always project the data to Alaska Albers:
- -PROJ_INFO-------------------------------------------------
name       : Albers Equal Area
proj       : aea
datum      : nad83
a          : 6378206.4
es         : 0.006768657997291279
lat_1      : 55
lat_2      : 65
lat_0      : 50
lon_0      : -154
x_0        : 0
y_0        : 0
no_defs    : defined
- -PROJ_UNITS------------------------------------------------
unit       : meter
units      : meters
meters     : 1


On Mar 15, 2007, at 1:43 PM, Brent Wood wrote:

> 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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>
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Gary Sherman
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