Free choice of projection center and map rotation?

LaskarisLaskaris Global Mapper UserPosts: 6
edited August 2013 in Projection Questions
I am thinking about buying Global Mapper. I need a program where I can freely choose the projection center of a map and rotate the projection around it, in the equirectangular projection. For instance, I would like to be able to choose a projection center at 44 N, 166 W and a rotation of -129 so that Australia is at the "north pole" of the map. I am currently using a program called Geocart for this, but it does not have the capability to use GIS data like Global Mapper, which I would like to have.

Can Global Mapper do this? I did not find any such functionality in the trial version.

Comments

  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited August 2013
    Yes, just load your data in the proper native projection, then go to the Projection tab of the Configuration dialog and choose a projection like Orthographic where you can enter a Central Meridian and Origin Latitude and a rotation angle to get the exact center and view that you need.

    Thanks,

    Mike
    Global Mapper Guru
    geohelp@bluemarblegeo.com
    Blue Marble Geographics for Coordinate Conversion, Image Reprojection and Vector Translation
  • LaskarisLaskaris Global Mapper User Posts: 6
    edited August 2013
    Thank you for your reply. The orthographic projection is not really suited for what I need to do, though. I would need something in the equirectangular projection, like this:

    tilted_earth.jpg

    Actually, is it possible to transform the coordinates in Global Mapper somehow, so that in the above example, Australia really is at the north pole (90N)?
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited August 2013
    Oh wow that is quite the interesting projection. That does look like you rotated the whole globe around so that Australia is at the north pole then did a Geographic (equirectangular) projection of that. I bet one of the projections in Global Mapper can be made to behave like that with the right parameters, I just don't know which one :)

    Thanks,

    Mike
    Global Mapper Guru
    geohelp@bluemarblegeo.com
    Blue Marble Geographics for Coordinate Conversion, Image Reprojection and Vector Translation
  • LaskarisLaskaris Global Mapper User Posts: 6
    edited August 2013
    Yes, that is exactly what I am looking for, basically: free choice of rotation angle in the Geographic (equirectangular) projection. When it comes to maps in image formats like .jpeg, I can do that with Geocart 3. But I would like to be able to do it with netcdf files (like the ETOPO .grd data from NASA), and to use the elevation data analysis tools of Global Mapper on these projections.

    The only projections I have found in Global Mapper that have a "rotation angle" option are Azimuthal Equidistant, Gnomonic, Orthographic, Polyconic and Transverse Mercator. Unfortunately, none of them are of use for what I am trying to do. Because I need to work with climate simulation software, I would really need the option to rotate a projection in the Geographic (equirectangular) format.
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited August 2013
    I don't think the rotation would be enough for Geographic. You also would need a way to re-base the pole at some other lat/lon location. Actually that might take care of the rotation itself since if you re-based some point in Australia to be the North Pole the rest would just happen automatically. I don't know that the math for that is quite as simple as just offsetting all lat/lon values to be relative to the new pole or not, I would have to think on it. If it was that simple you could even fake it in Excel with an XYZ file.

    Thanks,

    Mike
    Global Mapper Guru
    geohelp@bluemarblegeo.com
    Blue Marble Geographics for Coordinate Conversion, Image Reprojection and Vector Translation
  • LaskarisLaskaris Global Mapper User Posts: 6
    edited August 2013
    Well, the way it works in Geocart 3 is that one chooses a projection center (latitude and longitude) and the rotation around that center. The way I put Australia at the north pole in the example I showed you was by choosing a projection center of 44 degrees north and 166 west, and a rotation of -129 transversal.

    Anyway, thank you for thinking on it.
  • LaskarisLaskaris Global Mapper User Posts: 6
    edited August 2013
    I have found a solution for what I am trying to do. There is a Photoshop plugin called Flexify 2, developed by Flaming Pear. It can be used for map projections, including the rotation of maps in any of the available projections. I can load a TIFF file into Photoshop, do the rotation with the Flexify 2 plugin, and then load the modified TIFF into Global Mapper.
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