Cartesian vs Geographic Coordinates Accuracy RRS feed

  • Question

  • When it comes to accuracy, specific to surveying, would geographic coordinates be more accurate compared to cartesian? We're in the process of deciding if we should store our data in a geograhic coordinates spatial reference system (SRID), or still use cartesian.

    A prime example would be GDA94 vs MGA94 in Australia. Some state that cartesian might be more accurate. If cartesian, would it be Normal Mercator or Transverse Mercator?

    Any advice / direction would be appreciated.


    Thursday, May 19, 2011 6:54 PM


  • I'm not massively familiar with Australian coordinate systems but, from my understanding, MGA94 is simply a Transverse Mercator projection of GDA94. So it's not that either is "more accurate" than the other - they're both based on exactly the same datum (the geocentric datum of Australia), and the "accuracy" of those coordinates depends entirely on the accuracy of the system used to gather them. What's more, you can't ever increase the accuracy of coordinates from the accuracy in which they were originally supplied.

    So, if you have GDA94 coordinates, then they would be most accurately stored using the geography datatype. If you're given MGA94 then use the geometry datatype.

    This link seems to provide a good overview of concepts related to coordinate systems etc., with an Australian spin: http://www.cage.curtin.edu.au/~will/datum.html

    twitter: @alastaira blog: http://alastaira.wordpress.com/
    • Marked as answer by andrieso Friday, May 20, 2011 6:51 AM
    Thursday, May 19, 2011 7:25 PM