[Proj] Re: Still trying to get SPCS Alaska Zone 1 working!
Oscar van Vlijmen
ovv at hetnet.nl
Mon May 22 00:50:02 EDT 2006
I found another amusing tidbit about the Alaska Zone 1 SPCS projection.
A test point not on the central line:
lat = 58.5; lon = -135; (decimal degrees, longitude is west)
The 'official' NGS calculator
produced an easting, northing of:
740933.648, 742902.522 meters
The formulae and data mentioned in:
NOAA Manual NOS NGS 5, State Plane coordinate system of 1983
gave me an easting, northing of:
The NGS 5 manual specifies a false easting, northing of:
x0 = 5e6; y0 = -5e6; (meters)
My omerc version at first gave the wrong answer, but the correct answer
emerged when I set the no_ofs flag, as was mentioned earlier:
Now a surprise.
The PROJ.4 file "nad83" has for the false easting, northing of this region:
With these I can use omerc in the regular manner, without specifying a
The resulting easting, northing I got were:
These 'offset' values of x0, y0 can also be found in the file "nad1983." in
the USGS GCTP Fortran distribution. How they are derived, I don't know.
The numbers have something to do with the 1e7 m shifted easting, northing of
the lat0, lon0 on the aposphere. I can reproduce the numbers, but don't ask
me about the theory...
It's nonetheless interesting to know that in this case (Alaska 5001) still
the regular omerc can be used!
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