[Proj] Still trying to get SPCS Alaska Zone 1 working!

[Gerald I. Evenden]

Hey. its all gobblydegook to me too.  Omerc is the most messed up
projection alive and each CS has their own little "twist."  I tried to embrace
the plethora of variations with the several "switches" within omerc.

Blame Hotine.  ;-)

On Thursday 18 May 2006 11:02 pm, Anthony Dunk wrote:
> I found the answer to my own question - finally...
>
> I found that I needed to add the +no_uoff parameter to get the same
> results as Corpscon and Mapinfo.
>
> The new command string is:
>
> cs2cs +proj=latlong +a=6378137.0 +rf=298.257222 +to +proj=omerc
> +a=6378137.0 +rf=298.257222 +lat_0=57d00'00.000N +lonc=133d40'00.000W
> +alpha=-36.8698976458 +k_0=0.9999 +no_uoff +x_0=5000000 +y_0=-5000000
>
> If I enter lon=133d40'00.000"W and lat=57N, now I get Easting=818676.73
> and Northing=575097.69.
>
> According to one of Gerald Evenden's documents "In some cases, an
> offset in the pre-rotated axis may need to be suppressed with the
> +no_uoff option.". Its gobbledegook to me - but hey it works!
>
> Anthony.
>
> --- Anthony Dunk <AnthonyD at rocketmail.com> wrote:
> > Hi,
> >
> > Can anyone explain to me why the US Govt document on NAD83 State
> > Plane
> > Coordinate System (see link below) says that the origin for Alaska
> > Zone
> > 1 is lat=57N lon=133'40W or Easting=5,000,000, Northing=-5,000,000,
> > but
> > when I run the Corpscon program with the appropriate setup it
> > projects
> > this lat/lon to Easting=818676.713, Northing=575097.689 ? I also
> > found
> > that MapInfo projects it to exactly the same Easting/Northing as
> > Corpscon.
> >
> > If I use PROJ's cs2cs command (Rel 4.4.7 31 March 2003) to convert
> > these lat/lon coordinates using the following command:
> >
> > cs2cs +proj=latlong +a=6378137.0 +rf=298.257222 +to +proj=omerc
> > +lonc=-133.6666666667 +lat_0=57 +alpha=-36.8698976458 +k=0.9999
> > +x_0=5000000 +y_0=-5000000  +a=6378137 +rf=298.257222101
> >
> > Then I get Easting=4999999.80 Northing=-5000000.0.
> >
> > So, the PROJ command gives results which agree with the NAD83 SPCS
> > document, but both Corpscon and MapInfo give a consistent but
> > different
> > result. What is going on, and who is correct ??!
> >
> > Thanks,
> > Anthony.
> >
> > NAD83 SPCS document:
> > http://www.ngs.noaa.gov/PUBS_LIB/ManualNOSNGS5.pdf
> >
> >
> >
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