Converting to WGS84

From OpenStreetMap

Every country tends to have their own representation of geographical coordinates, this is usually to be able to have "flat maps" where you can draw a line and calculate the number of meters.

See http://www.geocities.com/mapref/dat/dat.html for some numbers.

Contents 1 Great Britain 2 Sweden 3 Austria 4 France

Great Britain

Converting to and from OS Grid (OSGB), using the proj tool:

PROJECTION
  "proj=tmerc"
  "lat_0=49.000000000"
  "lon_0=-2.000000000"
  "k=0.999601"
  "x_0=400000.000"
  "y_0=-100000.000"
  "ellps=airy"
  "towgs84=375,-111,431,0,0,0,0"
END

See gps.gov.uk for the calculations behind this.

Sweden

Converting to and from RT90, Using the proj tool.

# from GPS (15.806283 == 15d48.377)
$ proj -r +ellps=WGS84 +proj=tmerc +lat_0=0 +lon_0=015d48.377m +k=1.0000056 +x_0=1500064.1 +y_0=-668.0
# from RT 90
$ invproj -r +ellps=WGS84 +proj=tmerc +lat_0=0 +lon_0=015d48.377m +k=1.0000056 +x_0=1500064.1 +y_0=-668.0

Austria

Converting to and from BMN using proj.4 on meridian strips

M34: +proj=tmerc +lon_0=16d20 +x_0=750000 +ellps=bessel
M31: +proj=tmerc +lon_0=13d20 +x_0=450000 +ellps=bessel
M28: +proj=tmerc +lon_0=10d20 +x_0=150000 +ellps=bessel

In order to convert between WGS84 and MGI add

+ellps=bessel +towgs84=577.326,90.129,463.919,5.137,1.474,5.297,2.4232

You cannot use "proj" directly but have to use "cs2cs" instead. Only this "allows translation between any pair of definable coordinate systems, including support for datum translation" (from the man-page of proj).

An example for M28 looks like this:

 cs2cs +proj=tmerc +lon_0=10d20 +x_0=150000 +ellps=bessel \
          +towgs84=577.326,90.129,463.919,5.137,1.474,5.297,2.4232 \
       +to \
       +proj=latlong +datum=WGS84

France

There are several projection used in France, depending on the use (just an area/the whole land) and the current standards (yes, it's a mess...). The IGN detailled it

Here are the esri codes :

• Lambert Zone I = (ESPG:"Lambert Nord") code 27561
• Lambert Zone II = (ESPG:"Lambert Centre") = code 27562
• Lambert Zone III = (ESPG:"Lambert Sud") = code 27563
• Lambert Zone IV = (ESPG:"Lambert Corse") = code 27564
• Lambert I Carto = (ESPG:"Lambert zone I") = code 27571
• Lambert II Carto/étendu = (ESPG:"Lambert zone II etendu") code 27572
• Lambert III Carto = (ESPG:"Lambert zone III") code 27573
• Lambert IV Carto = (ESPG:"Lambert zone IV") code 27574