Alaska state plane zone 1 problems

geostotle

I'm running GM v10.02.
Coordinate conversions are working correctly when I convert grid coordinates from UTM, or a custom LDP to AK zone 1. But the lat/lon values are incorrect.

Can anyone confirm this?

1. Under projection, set to Alaska Zone 1 (FIPS 5001), Datum = NAD83, Planar Units = Feet (US Survey)
2. Import the attached point file (format is P,N,E,Z,D), or make your own file from:
26,2393134.5947,2488985.6424,26.3941,GPS_BC2"_FCF-26
27,2395945.6147,2498397.7916,146.1614,GPS_BC2"_FCF-27
3. Click the inquiry tool and choose either point. The lat/lon value displayed should agree with Corpscon, but does not.
26 should be N58°22'54.4753" W134°41'34.0137"
27 should be N58°23'23.5286" W134°38'38.2371"

GM misses Corpscon by about 15 feet in lat & about 30 feet in lon.

global_mapper

I took a look and discovered that the State Plane definition for Alaska Zone 1 provided by the USGS in their GCTPC library (which GM uses for many projections) was based on Hotine Oblique Mercator B and was slightly different than the more common modern definition using the Hotine Oblique Mercator Azimuth Natural Origin projection (which doesn't existing in v10). I was getting the same results as you in v13.1, but I changed the definition of that zone (the only one in the entire country based on Oblique Mercator) to the one using the Azimuth Natural Origin flavor of Oblique Mercator and now I get the exact same results as Corpscon.

I can provide a new v13 build with this change, but there isn't any way to back-port it to a v10 build as the base projection that is needed to get the exact same results doesn't even exist in v10. I have placed a new build at http://www.globalmapper.com/global_mapper13.zip with the latest changes for you to try. Simply download that file and extract the contents into your existing v13.xx installation folder to give it a try. If you are using the 64-bit v13 version there is a new build at http://www.globalmapper.com/global_mapper13_64bit.zip .

Let me know if I can be of further assistance.

Thanks,

Mike
Global Mapper Guru
gmsupport@bluemarblegeo.com
http://www.globalmapper.com