apply change projection from lat long wgs84 greenwich to custom prime meridian
I am trying to convert a world shoreline file from wgs84 latlong prime meridian Greenwich to the same latlong geographical with prime meridian set to 179 degrees. In fact I need to centrally display and digitize features in the Pacific region without having the cutline. I have tried several times with the "Project command" choosing the output coordinate system a new projection saved from the wgs84.prj edited with the modified prime meridian set to 179 (please see prj zip file attached).
When I click thr OK button an error message appears telling me "undefined geographic projection"' and if I want to choose the geographic transformation (optional)I do not have a choice which is obvious since I only want the prime meridian to change not the datum or ellipsoid.
The only way that itseems to work is to have the shapefile transformed into a projected shapefile like world robinson after having changed the central meridian from Greenwich the meridian I want, i.e.the 179 degree. After that I have created a new mxd with a custom projection set to latlong geographic wgs84 prime meridian 179. However in this way is just a "virtual" projection because the shapefile is displayed on the fly as I wish but in reality the projection file did not change. I have seen it works also with the mxd projection set to standard geographic (wgs84 prime meridian Greenwich)but the terms do not changes because I cannot produce the new projection file to apply for example to a raster for raster projection.
I wonder if there is a way to produce a new world shapefile with geographical projection WGS84 prime meridian different from Greenwich and have it displayed centered on the new chosen prime meridian.
Mapping Center Answer:
There are a couple of ways to do this:
1. Create a new coordinate system and transformation method. Here are the steps:
A. Using ArcCatalog browse to the C:\Program Files\ArcGIS\Coordinate Systems\Geographic Coordinate Systems\World folder. Select and copy the WGS 1984.prj file; naming the copy WGS 1984 Dateline.prj
B. Double-click the new prj file to edit its properties and change the bottom-most property for central meridian to <custom> and then type over "<custom>" with "Date Line" and then set the value in the degrees box to -180. Click OK to save the changes
C. Run the Create Custom Geographic Transformation tool using the following parameters:
- Geographic Transformation Name: WGS84_to_WGS84_Dateline
- Input Geographic Coordinate System: Browse to WGS 1984.prj and select it.
- Output Geographic Coordinate System: Browse to your neew WGS 1984 Dateline.prj and select it.
- Custom Geographic Transformation Method: Longitude Rotation (it's the last one).
D. Run the Project tool on your data--select WGS 1984 Dateline.prj as the Output Coordinate System. The Geographic Transformation list should now show WGS84_to_WGS84_Dateline as the only option.
All this said, I got rather poor looking results and don't recommend proceeding with that method. However, if your data were fairly simple and perhaps not covering the entire world this method may work well enough. I would also test both methods and see the resulting coordinates.
2. Use Plate Carree Projected Coordinate System instead. Here is how:
A. Project your WGS 1984 data to Plate Carree.
B. Project your Plate Carree data to Plate Carree, but modify the output project and change the Central_Meridian parameter, changing it from 0 to -180.
This produced a much cleaner geometric result. Either way, it won't remove the seams in Antarctica or Russia--you'll need to use the Editor and merge those afterwards. I would also note that my editing experiences with Shapefiles around the dateline were not so great--I would definitely recommend editing data in Geodatabase format (file, personal, or SDE will work fine).
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