[OSRS-PROJ] Pb with conversion betwenn WGS84 and Lambert
Frank Warmerdam
warmerdam at pobox.com
Thu Nov 20 14:08:47 EST 2003
Aurélie Lebreton wrote:
> Hello
>
> I want to transform a pair of angular coordinates in datum WGS84 to NTF
> Lambert 2. I have written this line :
>
> ./cs2cs +proj=latlong +datum=WGS84 +ellps=GRS80 +to +proj=lcc +lat_0=46.8000
> +lat_1=46.8000 +lon_0=2.3372291 +k_0=0.99987742 +x_0=600000 +y_0=200000
> +a=6378249.2 +b=6356515 +ellps=clrk80
>
> The input coordinates are :
>
> 2d39'48882"E 48d32'8575"N
>
> But the coordinates transformed come out wrong and i don't understand why :
>
> 1575621.19 743408.43 0.00
>
> (the coordinates should turn around these values :
>
> 600000 2400000
> )
>
> Does any one have the solution to this, or at least some in depth
> documentation on how to use proj ?
>
> Aurelie
Aurelie,
The main problem is your DMS specification: 2d39'48882"E. I imagine
you mean 2d39'48.882"E (that is 48.882 seconds, not 48882 seconds).
You may also find you need to include +towgs84=0,0,0 in the NTF coordinate
system to ensure that the ellipsoid conversion is done, even though no datum
shift info is available.
With the DMS specs fixed I get:
warmerda at gdal2200[265]% cs2cs +proj=latlong +datum=WGS84 +ellps=GRS80 +to +proj=lcc +lat_0=46.8000 +lat_1=46.8000
+lon_0=2.3372291 +k_0=0.99987742 +x_0=600000 +y_0=200000 +a=6378249.2 +b=6356515 +ellps=clrk80 +towgs84=0,0,0
2d39'48.882"E 48d32'85.72"N
624110.53 395817.08 83.91
This value looks reasonable. I am not sure why you were thinking the
northing should be in the range of 2400000m. 48d32' is less than 2 degrees
north of the reference point (46.8) and a degree is roughly 100000m. So
the value I got (395817m N) is roughly 2 degrees north of the reference point
which makes sense.
Note that without good datum shift information the precision of the
conversion will not be great.
Good luck,
--
---------------------------------------+--------------------------------------
I set the clouds in motion - turn up | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush | Geospatial Programmer for Rent
----------------------------------------
PROJ.4 Discussion List
See http://www.remotesensing.org/proj for subscription, unsubscription
and other information.
More information about the Proj
mailing list