[Proj] NAD27 to WGS84 ?

[Clifford J Mugnier]

Octavio,

Note that using those published 3-parameter values will yield no better
than 12-meter accuracy.  What I earlier suggested with respect to the
National Geodetic Survey has the potential accuracy improvement of more
than ten times better - IF such a data file exists for their software.

If accuracy to no better than 12 meters is sufficient for your needs, then
there's no need to contact NGS.

C. Mugnier

--------------------------------

Thank you Eric and everybody that contributed to answer my questions. It
is a good thing that a list like this one with such nice people
posting exists.

Octavio

On Wed, 22 Feb 2006, Eric Miller wrote:

> There are published "3-parameter" datum transformation values for NAD27
(Mexico) at:
>
>
http://earth-info.nga.mil/GandG/coordsys/onlinedatum/CountryNorthAmericaTable.html#NASL
>
> You can use the DX,DY,DZ values via the +towgs84 parameter for the source
projection.  Then, use the pj_transform() function to convert from
LCC/NAD27 to GEO/WGS84.
>
> Something like:
>
> src = pj_init_plus("+proj=lcc <your parameters here>
+towgs84=-12,130,190");
> dst = pj_init_plus("+proj=latlong +datum=WGS84")
>
> There's a fair amount of error in those conversions, but they're okay for
small-scale mapping.
>
> >>> opo at hp.fciencias.unam.mx 2/22/2006 9:30 AM >>>
>
> Hello,
>
> I'm new to the list, and to proj, and to Geography. I'm working in some
> maps for GPS receivers (Garming). One of the tools (graphical
> interface) for map creation (visualization) assumes the data is in
> lat/long datum WGS84.
>
> All the vector data available for Mexico is in lcc NAD27. The data is
> available in shapefiles for which I implemented a C program that
> successfully extracts the coordinates and translate them to lat/long
> in the NAD27 datum using the proj library.
>
> The questions are: Is it possible to shift (?) the data to WGS84 using
> proj?
>
> Which command/parameters should I use to do it?
>
> Any help will be really appreciated,
>
> Thanks,
>
> Octavio
>
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