[Proj] NAD27 to WGS84 ?

[Octavio Paez Osuna]

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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