[postgis-users] transform() does not do work for NGO1948 zone III -> WGS84 longlat (epsg:27393->epsg:4326)

[Mark Cave-Ayland]

> -----Original Message-----
> From: postgis-users-bounces at postgis.refractions.net [mailto:postgis-users-
> bounces at postgis.refractions.net] On Behalf Of Havard Tveite
> Sent: 20 December 2005 15:12
> To: postgis-users at postgis.refractions.net
> Subject: [postgis-users] transform() does not do work for NGO1948 zone III
> -> WGS84 longlat (epsg:27393->epsg:4326)

(cut)

> When using transform() in postgis, however, the longitude of origin
> (+lon_0=-10.72291666666667) seems to be ignored, and there seems to
> be no datum shift performed
> (+towgs84=278.3,93,474.5,7.889,0.05,-6.61,6.21).
> Longitude of origin (+lat_0=58) seems to be used correctly.


Hi Havard,

Actually, looking through the source lwgeom_transform.c I see the following
comment around line 500:

//this is *exactly* the same as PROJ.4's pj_transform(), but it doesn't
//do the datum shift.

So does this mean that the PostGIS transform() function won't do datum
shifts? Can anyone with a bit more PROJ4 knowledge say if this is correct,
and if so, why PostGIS can't support it?


Kind regards,

Mark.

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