[GIS] Reprojecting in postGIS from 900913 to 4326. Wrong coordinates

coordinate systemleafletpostgissrid

I'm working with postGIS 2.1
I have a table called 'xacementos' created with the srid: 900913. I took the points coordinates from google maps and I want to convert them to SRID:4326 to show the points in a map created over leaflet. (if a input the 900913 coordinates as geoJSON in the leaflet code the points show a little bit displaced)
I'm using the function ST_Transform:

SELECT ST_AsText(ST_Transform(geom,4326))
FROM xacementos
WHERE enderezo='Rua Franja 9-11';

but the coordinates that show up are not correct:

"POINT(-7.54315344075162e-005 0.000389606525237254)"

The input coordinates in the 900913 srid are "POINT(-8.397 43.3708)"

I'm newby in this postGIS stuff and I'm not sure if i'm following the right path.

Any suggestion??

Best Answer

I guess you are confused with what the different coordinates are.

EPSG:900913 (officially EPSG:3857) has an extent (worldwide) of

-20037508.34,-20037508.34,20037508.34,20037508.34

Your point (-8.397 43.3708) does not seem to be in this range (it's in portugal, right?)

This means that your point is in EPSG:4326 ("lat/lons") already.

You saying that "I took the points coordinates from google maps" confirms this to me, as google maps uses spherical mercator (EPSG:900913) internally, but it's api (and web pages) exposes all coordinates as EPSG:4326

Therefore, you should store your coordinates in PostGIS with EPSG:4326, and if this is what you need to get out there should be no need for transformations.

Related Solutions

[GIS] How to transform SRID 3035 to SRID 4326

At a guess, your point should be about 5.5km southeast of Bad Reichenhall right?

If so, the problem you have is you're interpreting your input coordinates incorrectly. The clue is in the source projection's name: LAEA which stands for Lambert Azimuthal Equal-Area, which is a projection that uses linear units (metres in this case) rather than angular units.

So your data of N2736 E4541 should be translated into metres - and here's the rub, they're in 1000's of metres, so your actual coordinate is 4541000, 2736000 (eastings are usually given before northings). If I use GDAL's gdaltransform:

$ gdaltransform -s_srs EPSG:3035 -t_SRS EPSG:4326

and type in the coordinates:

4541000, 2736000

I get:

12.9300691689392 47.6983999922817

Which puts me near the border between Bavaria and Austria.

In terms of PostGIS, you'd use:

SELECT ST_AsText(ST_Transform(ST_GeomFromText('POINT(4541000 2736000)',3035),4326));

Which returns me:

                st_astext
------------------------------------------
 POINT(12.9300691689392 47.6983999922817)
(1 row)

[GIS] KML from EPSG:4326 to EPSG:900913

i found a way to do it:

´format: new OpenLayers.Format.KML({
                extractStyles: true, 
                extractAttributes: true,
                maxDepth: 2,
                'internalProjection': options.projections.source, //EPSG:3785/900913
                'externalProjection': options.projections.display //EPSG:4326
            })´

Hope this helps anyone else :)

Best Answer

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[GIS] How to transform SRID 3035 to SRID 4326

[GIS] KML from EPSG:4326 to EPSG:900913

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