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I am after the EPSG code or Well Known Text (WKT) of a projection that puts the centre of the earth a 0,0,0 and each point is a cartesian XYZ distance from that.

My existing data is in WGS84 lat/long.

Does such a projection already exist? If not, any advice on do this projection? (I am very new to GIS)

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The arrangement you are (probably) looking for is Earth Centred Earth Fixed (ECEF). However I don't know if any "projection" like that. After all, its not really a projection - its just a coordinate conversion. Is that what you want to do? –  BradHards Mar 13 '13 at 10:06
    
Yes, I just want to convert from one coordinate system to another. (Apologies for mangling GIS terms - as I said I am very new) Is there some reference software or code to do want I want? (eg. Can I use GDAL in some way?) –  Damian Trebilco Mar 14 '13 at 0:03
    
I think I have it sorted from the answer below - thanks! –  Damian Trebilco Mar 14 '13 at 1:03

2 Answers 2

up vote 4 down vote accepted

I think you are using the term projection as a synonym for coordinate reference system. (Curse you, early Esrilites, for using that terminology!) EPSG identifies these as "geocentric" coordinate reference systems. In the online registry you can search for them through the Type by selecting Coordinate Reference Systems, Geodetic CRS, Geocentric CRS. The WGS 84 one is 4978 (geocentric CRS defined earlier usually have a 49xx code).

I've also seen this type of coordinate reference system called a 3D Cartesian system.

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Thanks, 4978 seems to be from initial tests what I want. For reference, I found these links useful for understanding: en.wikipedia.org/wiki/Geodetic_system en.wikipedia.org/wiki/ECEF stackoverflow.com/questions/2510574/… gis.stackexchange.com/questions/23660/… –  Damian Trebilco Mar 14 '13 at 0:59

Melita is quite right above. I'd add that a WKT representation of EPSG:4978 might look like:

GEOCCS["WGS 84",
    DATUM["WGS_1984",
        SPHEROID["WGS 84",6378137,298.257223563,
            AUTHORITY["EPSG","7030"]],
        AUTHORITY["EPSG","6326"]],
    PRIMEM["Greenwich",0,
        AUTHORITY["EPSG","8901"]],
    UNIT["metre",1,
        AUTHORITY["EPSG","9001"]],
    AXIS["Geocentric X",OTHER],
    AXIS["Geocentric Y",OTHER],
    AXIS["Geocentric Z",NORTH],
    AUTHORITY["EPSG","4978"]]

At least this is how GDAL/OGR reports it given the command gdalsrsinfo EPSG:4978. A transformation from WGS84 to that with the gdaltransform tool looks like:

 gdaltransform -s_srs WGS84 -t_srs EPSG:4978

An input of:

 -117 33

gives an output of:

-2430880.68434096 -4770871.96871711 3453958.6411779

Note that geocentric coordinates systems are not really that commonly used in GIS and interoperability between systems may be poor for such coordinate systems.

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