Issue with USGS Decade of North American Geology projection

[clementbataille]

Hi,

I have been using USGS grids (e.g. http://mrdata.usgs.gov/radiometric/). You can download a geosoft plu in for arcGIS to read this binary raster format. The problem I have is that those grids have a very peculiar projection (user defined datum and ellipsoid):
Here is the metadata:
 
            Map_Projection:

                Map_Projection_Name: Transverse Mercator
                Transverse_Mercator:

                    Scale_Factor_at_Central_Meridian: 0.926000
                    Longitude_of_Central_Meridian: -100.000000
                    Latitude_of_Projection_Origin: 0.000000
                    False_Easting: 0.000000
                    False_Northing: 0.000000

            Planar_Coordinate_Information:

                Planar_Coordinate_Encoding_Method: coordinate pair
                Coordinate_Representation:

                    Abscissa_Resolution: 0.000100
                    Ordinate_Resolution: 0.000100

                Planar_Distance_Units: meters

        Geodetic_Model:

            Horizontal_Datum_Name: D_User_Defined
            Ellipsoid_Name: User_Defined_Spheroid
            Semi-major_Axis: 6371204.000000
            Denominator_of_Flattening_Ratio: infinity

    Vertical_Coordinate_System_Definition:

        Altitude_System_Definition:

            Altitude_Resolution: 0.000100
            Altitude_Encoding_Method: 

I tried to define this projection for my grid but ArcGIS10 does not want to define it. It comes back to undefined everytime I try to apply it.
Second problem I will run into if I manage to define the projection for this grid is that I will not be able to re-project  such a weird projection system in a more common projection? There are no transformation existing in ArcGIS.
This is a pretty commonly used projection in USGS, they actually use it for many of their geological data (Geological Map of North America, radiometric, gamma ray...etc...) but those datasets are all useless if you can not work with them in an other projection.
If somebody know what to do with this that would be great.

Clement

[MelitaKennedy]

Ah, yes, the DNAG coordinate system. See link for two different ways of assigning the coordinate system.

If you're going to use the well-known text version by using it in a .prj file at 10.1, you can use the "import" option and browse to the file to select it.

There aren't any geographic/datum transformations. One way to deal with it is to unproject the data to STM1987 and then try redefining (not reprojecting) it as NAD 1983.

Melita

[HollieClavering]

Hi,

How do you unproject data?

I downloaded Geosoft Grid files, was unable to maintain a defined projection (using the .prj method), so I converted it to an ESRI grid.  The grid looks fine in this projection, but I want to project it to WGS84.  This does not work well; resolution is lost. 

I tried to change the file DNAG projection by defining the projection to NAD83 but got an error.  Any
suggestions?


Thank you,
Hollie

[MelitaKennedy]

Hi Hollie,

Unprojecting data is converting it from a projected coordinate system to a geographic coordinate system, so using the Project Raster tool. If the Project Raster tool is losing precision, the default calculations it uses to pick an output cell size may be getting confused. Try setting some of the tool's or geoprocessing environment parameters.

Melita