Carthage datum in GM

robbo31robbo31 Global Mapper UserPosts: 3
edited October 2012 in Projection Questions
Hi All,

A quick qestion about the Carthage datum in Global Mapper (& kingdom which i believe uses the same set of projection parameters). It looks like the version of Carthage in GM uses the Clarke 1880 spheroid as it's basis where as ESPG/ESRI seem to base theres on the Clarke 1880 IGN . I know I can setup a new datum by hand but as i'm about to do some mapping in Tunisia potentially I thought i would raise this. Which version do you consider correct?:confused:

regards


John Robson

Comments

  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited October 2012
    John,

    It looks like the correct ellipsoid is indeed Clarke 1880 (IGN) and I will fix that, but the difference between Clarke 1880 and Clarke 1880 (IGN) is so tiny (about 5 cm in one axis and 15 cm in another) that unless you are doing survey-grade mapping (which likely you wouldn't with such an old datum) you won't notice any difference.

    Thanks,

    Mike
    Global Mapper Guru
    gmsupport@bluemarblegeo.com
    http://www.globalmapper.com
  • robbo31robbo31 Global Mapper User Posts: 3
    edited October 2012
    OK Thanks Mike,

    I'll bear that in mind would it be better to stick to WGS84 as the basis for maps in Tunisia rather than Carthage?

    regards

    John R
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited October 2012
    John,

    If you are creating new maps I would use a modern global datum like WGS84 just to simplify things. If you have any existing maps that you are working with that use the Carthage datum you can always convert to WGS84.

    I have placed a new build at http://www.globalmapper.com/global_mapper14.zip with the ellipsoid fixed for Carthage for you to try. Simply download that file and extract the contents into your existing v14.xx installation folder to give it a try. If you are using the 64-bit v14 version there is a new build at http://www.globalmapper.com/global_mapper14_64bit.zip .

    Thanks,

    Mike
    Global Mapper Guru
    gmsupport@bluemarblegeo.com
    http://www.globalmapper.com
  • robbo31robbo31 Global Mapper User Posts: 3
    edited October 2012
    Hi Mike,

    Using a mixture, probably alot of point locations data ie wells locations and blocks, grids etc some will be in Carthage, I'm expecting a whole host of different datums, projections etc and i'll have to try to make a project which minimises as many differences in CRS as possible. I usually use GM for this, quite alot of the data will end up in kingdom but i prefer to try and straighten out these problems before importing data in there. Then we will start to try making some new interpretations. Thanks for the new version i'm only on V13.2 though at the moment. I'll modify the datum i have in there it's not the end of the world i just wanted to be sure this was the case and i was going to be adding another error into the mix.

    regards

    John R
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