[postgis-users] ST_Transform troubles

[Mike Toews]

On 24 June 2011 01:19, Frans Knibbe <frans.knibbe at geodan.nl> wrote:
> POINT(6.86264236062518 53.3160795502069)
> There are two things wrong with this result:
> 1) The coordinates are in the wrong order (EPSG:4326 uses latitude,
> longitude).

They are in the correct order. Standards say "X, Y" which are "long,
lat". This convention is commonly confused, as "lat, long" is very
common.

> 2) There are too much significant numbers in the result (the implied
> accuracy was increased by ST_Transform).

It's "precision" (not "accuracy") that was increased. This is
generally a good thing, and is required to represent global positions
within fractions of a millimeter. The "significant digits" method of
determining precision does not work here as the actual re-projection
calculations are not simple.

> I would have expected a result like
> POINT(53.31608 6.86264)

You can format geometry any way you like, e.g. for reporting as
"53.31608N 6.86264E". But if you are passing data for applications,
keep to standard WKT and high precision if you can. The distance
between the high-precision and 5-decimal precision is about 16.5 cm,
which can be significant to many users.

-Mike