[GIS] Convert from EPSG:4326 to UTM in PostGIS

convertpostgisutm

I would like to convert from EPSG:4326 to UTM (30N/EPSG:32630 or 29N/EPSG:32629) in PostGIS. I do the following query but I get wrong results:

SELECT ST_AsText(ST_Transform(ST_GeomFromText('POINT(36.5277099609375 -5.86424016952515)',4326),32630)) As check;

I get "POINT(5262418.33128724 -839958.963432011)" when it should be something approximate to 243625.00,4046330.00 in UTM 30N. If I do the conversion from 4326 to UTM I get the right result but not from UTM to 4326.

What's wrong with the query?
And are there anyway to get the UTM timezone from the coordinates in
EPSG:4326 because I don't know if they belong to 30N or 29N?

Best Answer

There is something wrong with your data. POINT(36.5277099609375 -5.86424016952515) is on the southern Hemisphere at 36°E and 5° South.

I guess you rather want POINT(-5.86424016952515 36.5277099609375) which is close to the border of 29N and 30N.

The borders between the UTM zones are 6 degrees apart, starting from -180° in the West. But there are some exceptions around Norway.

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

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.

Best Answer

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[GIS] How to transform SRID 3035 to SRID 4326

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

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