[Proj] NAD27 to WGS84 ?

[Eric Miller]

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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