Postgis / proj 900913 to 4326 projection questions with Y coordinate

Question

It is old, but I can not find a solution.

When I want to do st_transform at coordinate 900913 for system 4326, the y coordinate will shift.

Example:

SELECT AsText (Transform (Transform (GeomFromText ('POINT (449760.25168159 6790560.4594059)', 900913), 4326), 900913))

here the starting point of destination is 900913 st_stransformed to 4326 and back to 900913. the result is not the starting point, y is different. (I will insert the result later, I do not have it).

I tried changing proj4text for 4326 by adding + nadgrids = @null as I read somewhere

proj4text for srid 4326 currently:

"select proj4text from space_ref_sys file, where srid = 4326" + proj = longlat + ellps = WGS84 + datum = WGS84 + no_defs

proj4text for srid 900913 currently:

 msgstr "select proj4text from spatial_ref_sys file, where srid = 900913" + proj = merc + a = 6378137 + b = 6378137 + lat_ts = 0.0 + lon_0 = 0.0 + x_0 = 0.0 + y_0 = 0 + k = 1.0 + units = m + nadgrids = @null + no_defs

I also tried to make a forecast from 900913 to another forecast to 4326, but I get the same point as the direct conversion from 900913 to 4326.

any ideas?

E.Yu.

Answer 1

What version of PostGIS are you using? I tried a request with this configuration: POSTGIS="1.5.2" GEOS="3.2.2-CAPI-1.6.2" PROJ="Rel. 4.7.1, 23 September 2009"and it works fine.

Despite this, I have some problems with coordinates 900913.

Answer 2

EPSG: 900913 - . EPSG: 3857, Mercator, .

- . , ​​.