Coordinate System – How to Convert Longitude 0-360 to -180 to 180

coordinate systemfortranlatitude longitude

I have a netCDF file that contains climate data in a Gaussian grid. The longitudes are given from 0 to 360. I need to convert this to -180 to 180.

Is this the correct formula –

If longitude is greater than 180 subtract 360

I am looking to do this in Fortran.

Best Answer

Here is an example for fortran:

Variables in explanation:
long1 is the longitude varying from -180 to 180 or 180W-180E
long3 is the longitude variable from 0 to 360 (all positive)
To convert longitude from (0-360) to (-180 to 180)
 Matlab and fortran long1=mod((long3+180),360)-180

 Matlab long1=rem((long3+180),360)-180

 Fortran long1=modulo((long3+180),360)-180
To convert longitude from (-180 to 180) to (0-360)
 Matlab lon3=mod(lon1,360)

 Fortran lon3=modulo(lon1,360)
The “mod” function is Fortran is equivalent to “rem” function in Matlab.

The “modulo” function in Fortran is equivalent to “mod” function in Matlab.

http://vikas-ke-funde.blogspot.com/2010/06/convert-longitude-0-360-to-180-to-180.html

Related Solutions

GDALWarp – Reprojecting Raster and Cutting 180 Meridian

You could explicitly set the output coordinate range using the target extent option to gdalwarp (ie. "-te -180 -90 180 90") but you can also use the CENTER_LONG configuration option to force rewrapping around a new central longitude. Something like this:

  gdalwarp -s_srs "+proj=longlat +ellps=WGS84" -t_srs WGS84 ~/0_360.tif 180.tif  -wo SOURCE_EXTRA=1000 \
           --config CENTER_LONG 0

Note also the "SOURCE_EXTRA=1000" warp option. When doing rewrapping the source rectangle computation will get confused around the longitude interruption and lose some imagery. This option says pull in some extra. Without it you will see a data gap near the prime meridian.

I think that setting a prime meridian of 180dW as you did is not a good idea.

Shapefile – Changing Longitude Range from -180-180 to 0-360

Using GDAL >= 1.10.0 compiled with SQLite and SpatiaLite:

ogr2ogr world_shifted.shp world.shp -dialect sqlite -sql "SELECT ShiftCoords(geometry,180,0) FROM world"

or:

ogr2ogr -s_srs EPSG:4326 -t_srs "+proj=longlat +ellps=WGS84 +pm=-180 +datum=WGS84 +no_defs" world_shifted.shp world.shp

Both commands produce a longitude offset of 180°, i.e. a prime meridian of -180° is considered. In fact:

>ogrinfo world_shifted.shp world_shifted | grep Extent
Extent: (0.000000, -90.000000) - (360.000000, 83.623596)

The difference between the two commands is that with a longitude offset (2nd try) data are simply reprojected using -180° as prime meridian, while shifting the coordinates geometries (1st try) are altered, even if the result is apparently the same.

EDIT
If there are parts in 0-180 that should not move, it's possible to adapt this working solution: https://gis.stackexchange.com/a/73164/22405

Clip the two parts:

ogr2ogr world_part1.shp world.shp -clipsrc -180 -90 0 90
ogr2ogr world_part2.shp world.shp -clipsrc 0 -90 180 90

Shift only the first part:

ogr2ogr world_part1_shifted.shp world_part1.shp -dialect sqlite -sql "SELECT ShiftCoords(geometry,360,0), CNTRY_NAME FROM world_part1"

Then, merge the second part and the first shifted:

ogr2ogr world_0_360_raw.shp world_part2.shp
ogr2ogr -update -append world_0_360_raw.shp world_part1_shifted.shp -nln world_0_360_raw

Finally, dissolve countries boundaries of world_0_360_raw.shp obtaining world_0_360.shp by country names. For instance:

ogr2ogr world_0_360.shp world_0_360_raw.shp -dialect sqlite -sql "SELECT ST_Union(Geometry), CNTRY_NAME FROM world_0_360_raw GROUP BY CNTRY_NAME"

Best Answer

Related Solutions

GDALWarp – Reprojecting Raster and Cutting 180 Meridian

Shapefile – Changing Longitude Range from -180-180 to 0-360

Related Question