topic SDE ST_Transform gives wrong geometries from 3857 to 4326 in Data Management Questions

SDE ST_Transform gives wrong geometries from 3857 to 4326

GianniContino — Fri, 09 Oct 2015 07:47:15 GMT

Hi All,

I made a transformation of a circle with radius of 1000 mt. from 3857 (Web-Mercator) to 4326 (WGS84).

I issued a strange situation: the projected circle has a radius of around 0.7 meters.

What happens?

Thanx in advance

Re: SDE ST_Transform gives wrong geometries from 3857 to 4326

NeilAyres — Fri, 09 Oct 2015 07:49:20 GMT

4326 WGS84 is a geographic coordinate system based in degrees not metres.

Re: SDE ST_Transform gives wrong geometries from 3857 to 4326

GianniContino — Fri, 09 Oct 2015 09:33:28 GMT

I know.
But my problem is different:
I insert a circle (radius = 1000 meters in EPSG:3857 Web Mercator, in Meters);

after I transform it in WGS84 (in degrees);

In ArcMap by a tool I measure the radius (the tool returns length in Meters, etc...) and radius is 700 meters, not 1000 m.

I think it's an issue of SDE.ST_Transform

Re: SDE ST_Transform gives wrong geometries from 3857 to 4326

NeilAyres — Fri, 09 Oct 2015 11:02:21 GMT

I very much doubt that the projection is being handled incorrectly.

But what is your purpose for this?

And I ma surprised that your output is still a circle with a particular radius.

Depending on where it has been placed (high latitudes vs an equatorial location), I would expect that the Web Mercator version gets quished into some sort of ellipse in degrees.

Re: SDE ST_Transform gives wrong geometries from 3857 to 4326

VinceAngelo — Sat, 10 Oct 2015 02:28:12 GMT

You'll need to provide exact details of the version of ArcGIS, the database product, the database product version, the geodatabase version (if not the same as ArcGIS), the exact SQL you are using, and the coordinate values associated with at least one feature. You'll also need to provide how you determined that the radius was sub-meter in WGS84.

- V

Re: SDE ST_Transform gives wrong geometries from 3857 to 4326

GianniContino — Tue, 13 Oct 2015 18:18:01 GMT

Thanx I think I solved.

I was measuring distance in Planar instead of Geodesic distance.

the tool is the one of arcgis atcmap 10.2.2

@neil i know that the shape is such an ellipse, but all the axis where wrong