[postgis-users] Degrees to meters

[Barend Köbben]

You still do not understand apparently: your coordinates are ALWAYS in lat/lon as long as you use the SRID 4803, because that is an SRID that is defined as being a reference system on a sphere (or ellipsoid), indicating places on the surface of the sphere as  degrees from the centre of that globe (lat /long or lambda/phi). This is unlike a projected SRID using a Cartesian coordinate system: that is a projection of the spherical earth on a flat surface, , with the coordinates being X and Y (in meters of maybe feet or similar) from an origin.
 
As on of the first anwersers said: read a primer on map projections. A nice one is http://kartoweb.itc.nl/geometrics/
 
Good luck (and learning)!
 
-- 
Barend Köbben 
International Institute for Geo-information Sciences and  Earth Observation (ITC) 
PO Box 6, 7500AA Enschede (The Netherlands) 
ph: +31-(0)534874253; fax: +31-(0)534874335 

________________________________

From: postgis-users-bounces at postgis.refractions.net on behalf of Kevin martins
Sent: Wed 6/14/06 22:38
To: PostGIS Users Discussion
Subject: RE: Re: Re: Re: [postgis-users] Degrees to meters



Hi,
Let me see if i did understand.

I have the coordinates from GPS (WGS-84) that is :
  ->lat: 39.8263083333 N
 ->long: -7.43232906 E
And I want to convert first this coordinates to meters into Lisbon datum(4803).

I know the coordinates of the Lisbon datum reference point is:
  ->lat: 39.6666667 N
 ->long: -8.0116667 E

What I want to do is know the coordinates, in meters, of the point, in the two datum (lisbon datum and WGS-84 datum).

I have to create a new datum and then use the transform function?How can I use ellipsoid? the origin is the lonlat of the lisbon datum reference (my map is using the lisbon datum)??

Regards.
Kevin


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