[Proj] cs2cs how to use

[Clifford J Mugnier]

David,

You cannot go directly from WGS84 Datum coordinates to a projection (tmerc)
on another Datum without FIRST performing a Datum Shift.

Presumably, you are in Portugal, and the transformation parameters FROM
WGS84 Datum TO "Datum 73" are: dX=+223.116m ±0.11m, dY=-106.825m ±0.15m,
and dZ=-36.871m ±0.11m.  You will have to first implement the Molodensky
transformation subroutine with the above parameters to change Datums before
you then transform with the tmerc.  Note that for the Central Meridian that
you propose to use, the False Easting and False Northings appear to be
incorrect.

See my column on the Grids and Datums of the Portuguese Republic in
"Photogrammetric Engineering and Remote Sensing," April 2002, pp. 305-306.
This may be downloaded (no charge) in a pdf file from:
www.ASPRS.org/resources/grids.

I suggest you also download and read my column entitled "The Basics of
Datums," April 2000.

Good luck,

Clifford J. Mugnier, C.P., C.M.S.
Chief of Geodesy
Center for GeoInformatics
Department of Civil Engineering
LOUISIANA STATE UNIVERSITY
Baton Rouge, LA  70803
Voice:      (225) 578-8536
            (225) 578-4474
Facsimile:  (225) 578-8652
==========================================
http://www.ASPRS.org/resources/GRIDS
http://www.cee.lsu.edu/facultyStaff/mugnier/index.html
=========================================


Hello,

I'm new to proj and I need to convert some coordinates from wsg84 to tmerc.

The source coordinates comes from a gps device which uses wsg84 and I
would like to convert them to:

PROJCS["Datum_73_Hayford_Gauss_IPCC",
GEOGCS["GCS_Datum_73",
DATUM["D_Datum_73",
SPHEROID["International_1924",6378388.0,297.0]],
PRIMEM["Greenwich",0.0],
UNIT["Degree",0.0174532925199433]],
PROJECTION["Transverse_Mercator"],
PARAMETER["False_Easting",180.598],
PARAMETER["False_Northing",-86.99],
PARAMETER["Central_Meridian",-8.131906111111112],
PARAMETER["Scale_Factor",1.0],
PARAMETER["Latitude_Of_Origin",39.66666666666666],
UNIT["Meter",1.0]]

This info was taken from a ESRI *.proj file and I believe that it
contains all the information needed, but I haven't found the right way
to use it.

Can anyone help?

Thanks

David Vaz

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