Converting UTMs to Lat/Long?

Alex Barker

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Jun 8, 1993, 9:50:22 AM6/8/93

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Is there a package available to convert FROM UTM to
latitude/longitude? We're trying to convert archaeological
site locations to a format required by the administrative
agency overseeing the work (not a U.S. agency).

Any help appreciated.

Alex Barker
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Museum of Anthropology INTERNET: Alex....@um.cc.umich.edu
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Dan Civco

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Jun 8, 1993, 2:28:08 PM6/8/93

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> Date: Tue, 8 Jun 1993 09:50:22 EDT
Alex Barker writes:
re: Converting UTMs to Lat/Long?

Alex et al.:

One solution might be to consider "The Geographic Calculator" from
Resolution Mapping, Inc., River Road, P.O. Box 718, Newcastle, ME
04553. (207) 563-2311. The GC is a Microsoft Windows application that
enables conversion to-from Lat/Long, State Plane, UTM, Landsat WRS,
user defined coordinate and other systems. It sells for $225. This is
a solution if you don't have somehting like Arc/Info, in which these
CONVERTsions are standard fare.

Scott Kutz

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Jun 10, 1993, 9:19:00 AM6/10/93

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One method for converting between UTM coordinates and
latitude/longitude values is to utilize the General Cartographic
Transformation Package (GCTP, Version 2), available from the
National Geodetic Survey, NOAA.

GCTP is a VS/FORTRAN callable set of entry points which can be used
to convert between any two of the following 20 map projections
(forward and inverse transformations). Note that projections
to/from latitude/longitude are also supported by GCTP.

1. Universal Transverse Mercator (UTM)
2. State Plane (where the state plane projections are supported for
either NAD27 or NAD83, but not between NAD27 and NAD83)
3. Albers conical equal-area
4. Lambert conformal conic
5. Mercator
6. Polar stereographic
7. Polyconic
8. Equidistant conic
9. Transverse Mercator
10. Stereographic
11. Lambert azimuthal equal-area
12. Azimuthal equidistant
13. Gnomonic
14. Orthographic
15. General vertical near-side perspective
16. Sinusoidal
17. Equirectangular
18. Miller cylindrical
19. Van der Grinten I
20. Oblique Mercator (Hotine)

Note: Projection parameters are available with the GCTP package for
the State Plane projections and UTM projections. For the
other projections, the user must provide the appropriate
projection parameters when calling GCTP.

GCTP is available for a nominal fee ($98.00 US) and can be ordered
from the following:

National Geodetic Information Center
N/CG174, Rockwall Building, Room 24
National Geodetic Survey, NOAA
Rockville, Maryland 20852-3019
Tel: 301/443-8631
Fax: 301/881-0390

The GCTP package contains three physical files: one with the
VS/FORTRAN source code and two data files containing the State Plane
Coordinate projection parameters for both NAD27 and NAD83.

The GCTP documentation (NOAA Technical Report NOS 124 CGS 9) is pro-
vided along with the package. This documentation is an essential
reference for using GCTP. It includes the encoding information for
the manner in which concepts such as projection method, zone, and
measurement unit are provided to GCTP via the main entry point
GTRNZ0.

Based on recommendations from the National Geodetic Survey, for any
transformations which are made involving either state plane coordi-
nates or the Universal Transverse Mercator (UTM) projection, the
application should perform the transformation in two steps:

1. From the source coordinate system into geographic coordinates
(latitude/longitude).

2. From geographic coordinates (latitude/longitude) into the target
coordinate system.

This approach avoids any possible problems which may arise in the
case where both the "source" and "target" coordinte system use the
same underlying projection. For example, some state plane zones use
Transverse Mercator as their underlying projection. The Transverse
Mercator is also the basis for generating UTM coordinates. The
internal structure of the GCTP is such that it only allocates
storage for a single use at a time of a given projection. There-
fore, if both the "source" and "target" coordinate systems attempted
to use, say, the Transverse Mercator projection, the results of the
GCTP computations will not be valid. By using geographic coordi-
nates (latitude/longitude) as intermediate values, the type of
problem described above is avoided.

-- Scott
--
Scott Kutz internet: sk...@vnet.ibm.com
GIS Development phone: (914) 385-3135
IBM Corporation, Dept 44D/575 fax: (914) 385-1841
Neighborhood Road Disclaimer: All opinions are my own
Kingston, New York 12401 and not those of IBM.