[GRASS5] projection-transformation

[Morten Hulden]

Hi All, 

Since r.proj changed (beta9) I have had the general (totally subjective)
impression that projections of globe dem maps fit somewhat better than
those done with the old r.proj, but are shifted 0.5-1 resolution units to
the north and 0-0.5 resolution units to the east compared to gs coastline.
This happens in many different projections I have tried (laea, sweden-rt,
finland-ykj, norway-utm33). Your URL and the numbers below support those
observations.

I wonder where this smallish mismatch comes from; could be datum, could be
bug in r.proj or both.

But if this is a bug it's probably unrelated to the much larger mismatch
between the two vector maps. 

Morten


On Fri, 22 Dec 2000, Markus Neteler wrote:

> maybe it's a bug... (but where?). I made some further tests with my
> dataset by analysing a point:
> 
> The west corner of the "norderney" island (one of those islands in the
> picture I have sent the URL) has following points in the map (d.where):
> 
> UTM:
>  377261 5953152 (GSHHS dataset from v.in.gshhs [new, to be submitted soon])
>  377946 5953426 (GLOBE DEM 1km, generally matching to GSHHS quite well)
> 
>  379592 5952535 (Students vector data from ARC/INFO)
> 
> 
> I took a 1:100000 map of that area and got the coordinates in Gauss-Krüger
> system (tmerc, bessel):
>  2575400   5953800 GK
> 
> These I transformed with m.proj to UTM to compare them with d.where results:
>  377375 5953157 UTM
> 
> It seems that the ARC/INFO vector data are shifted:
>  > 2km to east
>  > 500m to south


---------------------------------------- 
If you want to unsubscribe from GRASS Development Team mailing list write to:
minordomo at geog.uni-hannover.de with
subject 'unsubscribe grass5'