[Proj] proj4 definition for transverse mercator projection from RegCM3 model for North America

[support.mn at elisanet.fi]

Hello,

You have different lon_0 ??!!

fwd: +lon_0=-97.0
inv: +lon_0=263

Are you sure your parameters are correct??

Regards: Janne.

=====================================

Hailey Eckstrand [haileyeckstrand at gmail.com] kirjoitti: 
> Hello all,
> I am trying to create the proj4 string for a netcdf file with the following
> coordinate information:
> 
> variables:
>         char Transverse_Mercator ;
>                 Transverse_Mercator:grid_mapping_name =
> "transverse_mercator" ;
>                 Transverse_Mercator:longitude_of_central_meridian = -97. ;
>                 Transverse_Mercator:latitude_of_projection_origin = 47.5 ;
>                 Transverse_Mercator:scale_factor_at_central_meridian = 1. ;
>                 Transverse_Mercator:false_easting = 3925000. ;
>                 Transverse_Mercator:false_northing = 3175000. ;
>         double lat(yc, xc) ;
>                 lat:units = "degrees_north" ;
>                 lat:long_name = "latitude" ;
>                 lat:standard_name = "latitude" ;
>                 lat:axis = "Y" ;
>         double lon(yc, xc) ;
>                 lon:units = "degrees_east" ;
>                 lon:long_name = "longitude" ;
>                 lon:standard_name = "longitude" ;
>                 lon:axis = "X" ;
>         double xc(xc) ;
>                 xc:long_name = "x-coordinate in Cartesian system" ;
>                 xc:standard_name = "projection_x_coordinate" ;
>                 xc:units = "m" ;
>                 xc:axis = "X" ;
>         double yc(yc) ;
>                 yc:long_name = "y-coordinate in Cartesian system" ;
>                 yc:standard_name = "projection_y_coordinate" ;
>                 yc:units = "m" ;
>                 yc:axis = "Y" ;
> 
> 
> The file gives the coordinates in their native projected coordinates as well
> as the lat & lon coordinates.
> 
> From this information, I created the following proj4 string:
> +proj=tmerc +lat_0=47.5 +y_0=3175000.0 +x_0=3925000.0 +lon_0=-97.0 +k_0=1.0
> +units=m +ellps=sphere
> 
> (The sphere ellipsoid is a guess as they didn't provide the geographic
> coordinate system.)
> So when I test out this proj4 string, these are the results I get:
> 
> proj -f "%f" +proj=tmerc +lat_0=47.5 +y_0=3175000.0 +x_0=3925000.0
> +lon_0=-97.0 +k_0=1.0 +units=m +ellps=sphere
> in> -126.0869 19.61229
> in> -125.6792 19.77242
> in> -125.2703 19.93048
> 
> out> 773317.154904   359897.643377
> out> 824089.485710   370794.986195
> out> 874706.342446   381466.440468
> 
> the projection coordinates should be:
> 600000   600000
> 650000   600000
> 700000   600000
> 
> and then the opposite transformation:
> 
> invproj -f "%f" +proj=tmerc +lat_0=47.5 +y_0=3175000.0 +x_0=3925000.0
> +lon_0=263 +k_0=1.0 +ellps=sphere
> in>  600000 600000
> in>  650000 600000
> in>  700000 600000
> 
> out>  -127.929260     -21.210147
> out>  -127.514502     -21.293413
> out>  -127.097731     -21.375966
> 
> and the coordinates should be:
> -126.0869 19.61229
> -125.6792 19.77242
> -125.2703 19.93048
> 
> The longitude are at least in the ballpark, but the latitudes are completely
> off.
> 
> If it helps, this data has been downloaded from NARCCAP, and it is the
> RegCM3 model.
> Any help would really be appreciated.
> Thanks in advance,
> Hailey
> 
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