I've got a POINTS PostGIS table in the 23030 (ED50 UTM 30N) SRID.
I'm having a lot of problems trying to reproject those points from ED50 UTM coordinate system to ETRS89 Geographic (lat/long) coordinate system. The aim is to convert the points for Google Maps.
I take an example point for my tests:
x: 499462.1 y: 4799340.56
1.- If i just transform the point from UTM (23030) to Geographic lat/long (4230) using the
ST_TRANSFORM("GEOMETRY",4230) PostGIS function. I get the following coordinates:
long: -3.00663639334493 lat: 43.3461345057409
You can see in the picture where it is located in Google Maps. It has sense to be located in a different place to the original point, because although being in Geographic projection system it is not in ETRS89/WGS84.
2.- So I reproject the original point first to ETRS89 (nearly the same as Google's WGS84) using
ST_TRANSFORM("GEOMETRY",25830) and I get the following point:
Ok, if I load that point in a GIS, I can see there is a difference between the previous point which is ok as I have changed the SRID.
3.-I thought that if I reprojected the ETRS89 UTM point to ETRS89 lat/long it would be enough for getting the coords valid for Google Maps. The surprise came when I got the same point of the step1!!! (just doing the 4230 transformation)
I used a
ST_TRANSFORM(ST_TRANSFORM("GEOMETRY",25830),4258) UPDATE query applied to the original point.
I don't really know how to solve this mess, I'm really confused.