[OSM-dev] Units in the PostGIS database - what are they?

Dirk-Lüder Kreie osm-list at deelkar.net
Sat Mar 17 23:14:00 GMT 2007

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Nick Whitelegg schrieb:
> I'm getting unexpected results with the units used in the PostGIS database - 
> namely they don't seem to be metres. I would expect metres out of a Mercator 
> projection.

UTM easting should be metres, yes.

> Using Nick Burch's Where Am I? script, the distance between the villages of 
> Fernhurst, West Sussex and Cheriton, Hampshire is 31km - they are on the same 
> latitude. From my knowledge of the area, 31km or about 20 miles seems about 
> right.
> However, the difference between the eastings is greater than 31000 metres.

However, UTM easting is never negative AFAIK.

> Cheriton has an easting of approximately -130000. Fernhurst has an easting of 
> approximately -80000, giving a distance of 50km if the units were metres.... 
> so clearly they are not. 

According to Google Earth Cheriton has an approximate easting of 628000
while Fernhurst has an approximate easting of 660000 giving a distance
of 32 km or approximately 20 miles

> Also, Fernhurst is less than 80km west of the Greenwich Meridian - more like 
> about 50-60km.
> So... what units are the PostGIS coordinates in?

Apparently not UTM

Dirk-Lüder "Deelkar" Kreie

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