How do I convert State Plane coordinates to latitude-longitude?

Question

Given a specific state plane coordinate system (whether NAD27 or NAD83), are there any resources to convert to latitude-longitude?

Answer 1

You'll need to reproject them to handle this conversion.

Proj.4 is a very standard library, used by a lot of software for reprojections.

One means of using this would be to use a utility like gdaltransform to do the transformation for you.

Answer 2

If you know the relevant EPSG codes or proj.4 parameters, both gdaltransform and proj.4's cs2cs (man page) are a good route, as Reed mentioned.

However, if you find yourself without this information, try spatialreference.org: it provides the parameters, and a web map for doing a lat/long to coordinate system transformation (example with IL state plane). As many of the state plane projections lack an EPSG code, use sr.org to find the proj.4 string, which gdaltransform understands. Here's an example converting from California State Plane Zone V to WGS84 lat/long pairs:

gdaltransform -s_srs '+proj=lcc +lat_1=34.03333333333333 \ 
+lat_2=35.46666666666667 +lat_0=33.5 +lon_0=-118 +x_0=2000000 +y_0=500000 \ 
+ellps=GRS80 +units=m +no_defs' -t_srs epsg:4326

After which, typing 1815241.25377291 557301.336190851 should return -120 33.9999999999996.

Answer 3

Client or server? Language specific? One-off or bulk?

E.g. - for client side - with JavaScript - use OpenLayers + Proj4js.

0) Import all the appropriate libs

1) create your point

var lonlat = new OpenLayers.LonLat( ....)

2) convert it

lonlat.transform( new OpenLayers.Projection("epsg:XXXX"), new OpenLayers.Projection("epsg:4326"));

now lonlat.lon and lonlat.lat are in WGS84 lon/lat values.

Answer 4

One free and extremely easy program is CorpsCon which will convert single points, batches of points in text files, and has a DLL that can be used from within programing environments like python.

Answer 5

If you want to build it yourself, here's a document from the National Geodetic Survey that describes the transformations:

http://www.ngs.noaa.gov/PUBS_LIB/ManualNOSNGS5.pdf

You'll still need to know the specific parameters for the projection of interest.

Answer 6

Another option (but just for NAD83) is SPCS83 at http://www.ngs.noaa.gov/PC_PROD/SPCS83 . It runs in a command line window on a PC and converts either interactively or from a text file input. It includes source code if you really just want the algorithm. Source is Fortran, which may be a pain to use but is easy enough to decipher to get the algorithms out. Also see www.metzgerwillard.us/spcge/spcge.html which is a front end for SPCS83 in Google Earth.

Answer 7

Check out the free translation service. Upload your data and then specify the desired output coordinate system. By selecting the same format for output as the input you are effectively doing a reprojection.

The service is found at http://fmeserver.com/userweb/sharper/Portal/EasyTranslator/index.html

and is based on the FME product. There is also a free 14 day trial of this as well. www.safe.com