[postgis-users] ST_Transform troubles

[Ralf Suhr]

Hello Mike,

there are 2 standards PostGIS and most other software use the 
http://en.wikipedia.org/wiki/Right_hand_rule.

In surveying only the "left hand rule" is the truth.

Gr
Ralf

Am Donnerstag 23 Juni 2011, 16:05:18 schrieb 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
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