New projection for french online maps (www.geoportail.fr)

I found in this document
the RRAF1991 is the same than the WGS84 (a = 6378137m and RF = 298.2572221010000)
The projection is described as geocentric for both of them.

And for those who would be interested in more specific details about gps and lambert93, i found this document very accurate.

With these new data, I presume I have to choose WGS84 for datum but which type of projection should I use (lat/long ?) ?

Thanks in advance for your precious help.

Bzh972 wrote:

Hi;

try with:

http://www.eye4software.com/resources/grid/2989/

Transverse Mercator

orux

in plain text so: first doc is http lambert93.ign.fr fileadmin files IGNF (you'll have to replace spaces by slashes)
and second doc is http rev pdf 68_91.pdf

Bzh972 wrote:in plain text so: first doc is http lambert93.ign.fr fileadmin files IGNF (you'll have to replace spaces by slashes)
and second doc is http rev pdf 68_91.pdf

No links if no register;

try with:

http://www.eye4software.com/resources/grid/2989/

Transverse Mercator

orux

Thanks for your link, it seems very accurate too.

Sorry for the multiple post but I encountered some troubles inserting URL in my posts (maybe because writing as a guest?)
you can remove them and/or edit them to insert the links (the latest one is incomplete the server address is www geomag fr)

first doc
second doc

I'll try with your suggestion and keep you advised of the success.

Thanks

Gael

As far as I tried til now, the best projection to use with geoportail tiles for martinique is Mercator.
It gives me only a slight deviation, moreover maybe due to the approximative coordinate values given to the desktop.
For example, on a 12km track, the max deviation is between 5 and 10 meters, always to the south (which leads me to think that the problem comes from my given coordinates)

I tried with the Transverse mercator you suggested using parameters given by your linked website but it shows me about 300 meters south to my supposed position on the map.

I keep looking for the most efficient projection and coordinates conversion system.

Since the tiniest the map is, the most accurate the position is, maybe it would be more efficient to have a lot of little maps instead of a only big one.
What's your point of view? If yes, is there a way to calibrate each tile separately then to make the all of them works as if it were a only one (for example being able to select a map which would load all the little ones in a raw)?

Thanks for your help

Gael

Bzh972 wrote:As far as I tried til now, the best projection to use with geoportail tiles for martinique is Mercator.
It gives me only a slight deviation, moreover maybe due to the approximative coordinate values given to the desktop.
For example, on a 12km track, the max deviation is between 5 and 10 meters, always to the south (which leads me to think that the problem comes from my given coordinates)

I tried with the Transverse mercator you suggested using parameters given by your linked website but it shows me about 300 meters south to my supposed position on the map.

I keep looking for the most efficient projection and coordinates conversion system.

Since the tiniest the map is, the most accurate the position is, maybe it would be more efficient to have a lot of little maps instead of a only big one.
What's your point of view? If yes, is there a way to calibrate each tile separately then to make the all of them works as if it were a only one (for example being able to select a map which would load all the little ones in a raw)?

Thanks for your help

Gael

Hi;

Send me one of your maps (original, the image)--> oruxuro@gmail.com

You can join maps using globalmapper.

orux

Here you can download IGN maps of France and Belgium.

Enjoy....