[Proj] Convert X and Y to Lat and Lon

[don_nell]

Hello, 

I'm very new to mapping and I'm trying to use cs2cs.exe from Proj4 to
convert the X and Y values from an ESRI shape file (roads from the state of
Georgia) into Lat and Lon coordinates.  However, I'm not sure what
parameters I need  to accomplish this. 

I've gotten pretty close using the parameters below (plus or minus a city
block), but I'm sure I could do better.

+proj=tmerc +units=us-ft +datum=NAD83 +lat_0=-1.77517 +lon_0=-83.5 +k=0.9999
+x_0=0.0 

The "+lat_0" parameter was derived by trial and error. 

Can anyone tell me the correct parameters to use to make this work? 

The contents of the associated .prj file are as follows. 

Thanks in advance. 

Don 

PROJCS["NAD_1983_Georgia_Statewide_Lambert",GEOGCS["GCS_North_American_1983",DATUM["D_North_American_1983",SPHEROID["GRS_1980",6378137.0,298.257222101]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]],PROJECTION["Lambert_Conformal_Conic"],PARAMETER["False_Easting",0.0],PARAMETER["False_Northing",0.0],PARAMETER["Central_Meridian",-83.5],PARAMETER["Standard_Parallel_1",31.41666666666667],PARAMETER["Standard_Parallel_2",34.28333333333333],PARAMETER["Latitude_Of_Origin",0.0],UNIT["Foot_US",0.3048006096012192]] 

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