Using State Plane Coordinate Systems in Garmin Receivers
(Rev. 26 Apr. 2003, Add Garmin User Grid Instructions -by Jack Yeazel)

During the 1930s, the U.S. Coast and Geodetic Survey (USC&GS), now NGS developed the State Plane Coordinate System which have been very popular at the local level. Many users find State Plane maps more adaptable than UTMs because the zone boundaries fall along political lines (e.g., State and County) as opposed to geometric lines. In addition, there is less "scale reduction" with State Planes when compared to UTMs, and distances are some four times as accurate.  Standards for The State Plane Coordinate System of 1983 can be found at:

The following procedure allows a Garmin Position Format "User UTM Grid" to display UTM State Plane coordinates directly:

State Plane point-of-origin data is difficult to find and takes considerable searching of the internet!   However, Peter Dana pointed me to and the file: tblspc.for -which has comma-separated-values data for all the State Planes in the US.  I have used about 20% of this file to create a spread sheet:  For a summary of the spread sheet, see this TEXT.

NOTE: This Excel file is required to obtain the data to enter into the GPS unit; however, it requires that you know which zone and whether the data you need is in the NAD-27 or NAD-83 datum beforehand.  State Plane zones can be determined from:

Example from the Georgia data:
                         Georgia West Zone 1002 (Includes Atlanta)
                                Latitude of Origin = 30° 00' 00"
                  Longitude of Origin and Central Meridian = 84° 10' 00"
                                 Datum = NAD-83
                                Scale = 0.9999
                    False Northing at Origin = 0 meters
                     False Easting at Origin = 700,000 meters

Settings for Garmin "User UTM Grid":
                       (Set Datum to the above state plane datum)
                              Longitude Origin = 84°  10.000'
                            Scale = +0.9999000 (1-1/10,000)
                             False Easting = +700,000m
                             False Northing = -3319781.0m*

*Tricking Garmin and Other “UTM-Like” User Grids into State Plane, Transverse Mercator Conversion

REMEMBER: The GPS will read out coordinates in meters which will have to be converted to the Survey Foot (see below).  OR if creating waypoints from State Plane coordinates, the feet must be converted to meters.  But once activated, the unit will display all data in State Plane coordinates.
   IMPORTANT NOTE: The "Foot" specified for NAD 27 and NAD-83 are what are commonly called "U.S. Survey Foot," which is related to the meter by 1 m = 3.280833333333.... ft. This is important, as you will often find the conversion listed in many sources as 1 m = 3.280839895 ft, which is referred to as the International Foot, adopted by the U.S. Bureau of Standards in 1959. Ignorance of these differences can easily distort your conversions by 10-15 ft!

 This Garmin procedure does NOT work for Lambert Conformal projections.
Magellan units display State Plane coordinates directly (even in survey feet) without a need for a "trick".  A procedure for these units is in progress, including display of Lambert Conformal Conic projections.  See (HERE) for review.

  When working with State Plane maps, watch the horizontal datums carefully. It is common to find current State Plane maps in NAD27 as well as NAD83. NGS/NOAA reports that there are significant positional differences between these reference systems.

State Plane,Transverse Mercator Conversion
Peter H. Dana - Department of Geography - University of Texas at Austin
July 1, 1999

The Garmin 12 XL User Grid (SW Ver 4.54) and other Transverse Mercator (TM) converters that have only a “UTM-like” user grid with a fixed Equator origin latitude can be "tricked" into emulating a complete TM grid with a non-zero latitude origin by computing the necessary false northing value to compensate for the incorrect latitude origin at 0.0 degrees. This is not too hard and is an exact "fix." This technique is useful when either using a true TM grid (about half of the NAD83 United States State Plane Coordinate Systems – usually those zones whose north-south extent exceeds their east-west extent) or emulating one (to approximate a Lambert Conformal Conic grid - most of the other half of the SPC zones). It is not useful for oblique projections such as the Alaska Zone 1 SPC (an Oblique TM projection) or grids that cover large areas over which the TM approximation of the correct projection will simply have too large an error.

The “normal” TM formulas (Snyder, John P. 1987. Map Projections: A Working Manual. USGS Professional Paper 1395. Washington, DC: US Government Printing Office) compute the northing value from a number of terms including two values of “true distance along the central meridian;” one for the position latitude (M) , and the other for the origin latitude (M0). This is the only place in the ellipsoidal TM formulas where the origin latitude is used. The northing value computed using a zero origin latitude (the Equator) is missing only a value of the TM scale (k0) multiplied by M0. If one knew the correct value for k0 * M0 we could just add that to the northing computed for the zero origin case. This k0*M0 value is a constant everywhere the projection is used.

 We can compute this k0*m0 value using the incomplete TM conversion in the Garmin 12XL:
 The “normal” TM parameters contain the following values (Here we will use Vermont's single NAD83 SPC zone (4400) as a good example of a TM grid).
 Origin Latitude 42:30:00N
 Origin Latitude 72:30:00W
 Scale Factor (1:28,000)
Scale (1-SF) 0.99996429
 False Easting  500,000 meters
 False Northing  0.0 meters

 To define the same grid in a “UTM-like” Garmin 12XL grid:

 Make sure the unit is set to the NAD83 geodetic datum (or the practically equivalent WGS-84)
 Set the position format to hddd°mm’ss.s”

 Define a waypoint in latitude and longitude at the desired TM origin latitude and longitude.
  NAME (A1 or any other name)
  N  42°30’00”

 Change the position format to User Grid
  User Grid
  W072°30.000 (note the need for decimal minutes here)
  00500000.0 mt
  00000000.0 mt*
*Even though an origin has a northing value, place zero here

 Return to the WAYPOINT LIST
  Locate the origin waypoint (A1)
  Find the Easting and Northing
             05000000 Easting
  USR      4707008 Northing
  Record the northing value (4707008)

 Compute the “trick” false northing by negating this origin false northing and add the true false northing (0.0 meters for this VT SPC zone).
  +         0.0

  Edit the User Grid to set the False Northing to this “trick” value.
  -4707008.0 mt

 Check the procedure by returning to the waypoint list. Note that now the origin of the TM system has its correct value of:
           0500000 Easting
  USR  0000000 Northing

  The program CORPSCON will allow you to transform very easily between NAD 27 and NAD 83 in any of the coordinate values you would like to use (e.g., State Plane, UTM or Lat/Long). To get a better understanding of some of the geodetic principles involved, see "Geodesy for the Layman"

  For individual points and tracks, public domain software that will perform conversions is available from the National Geodetic Survey/N.O.A.A. web site:
State Plane to/from Latitude & Longitude --SPCS83
UTM to/from Latitude & Longitude -- UTMS
Both of these programs have been compiled into a very user-friendly package, CORPSCON, by the U.S. Army Corps of Engineers. CORPSCON can be downloaded from:

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