[OSM-talk] Coastlines

[David Groom]

----- Original Message ----- 
From: "J.D. Schmidt" <jdsmobile at gmail.com>
To: "Andy Robinson" <Andy_J_Robinson at blueyonder.co.uk>
Cc: <talk at openstreetmap.org>; "'Steve Chilton'" <S.L.Chilton at mdx.ac.uk>
Sent: Monday, August 21, 2006 2:21 PM
Subject: Re: [OSM-talk] Coastlines


> Andy Robinson skrev:
>> That's not surprising as the Landsat data position is not that accurate.
>> There is a shift in the Landsat. In my Birmingham area I normally have to
>> slide items created off the Landsat imagery (railway lines and rivers 
>> etc)
>> by about 50m to the south west.
>>
>> Cheers
>>
>> Andy
>>
>> Andy Robinson
>> Andy_J_Robinson at blueyonder.co.uk
> After getting OJW to import PGS coastlines for my area here in Denmark, 
> the accuracy of the coastline is pretty good, even small marina quays 
> shows up.
> But it is evident there's a consistent shift to the south east. My 
> preliminary investigation shows that the coastline is about 30 meter south 
> and 18 meters east of where it should be. Square mentioned on the IRC 
> channel, that thediscrepancy of 30 meters S-N direction, and 18 meters E-W 
> direction is equivalent to about 1 arcsecond in both cases.
>
>
> I have so far only checked it at two places (a bit north of Copenhagen 
> near Hellerup, and at the end of the small island of Amager where 
> Copenhagen Airport is located.) I've checked it against the municipality 
> data at the danish KMS geo-portal site, as well as making gpx tracks and 
> plotted them on the high resolution Digital Globe 2006 sat images 
> available on gmaps for Copenhagen. In both cases they concur with the 30 
> meters south and 18 meters east shift. I'll post some screenshots on the 
> wiki later.
>
>
> The danish PGS coastline is not from the same set of the files where the 
> IoW data was imported. AFAIR the danish data comes from the CD21 data, 
> while the IoW data came from the CD19 data. But if it is the same 
> discrepancy of 1 arcsecond in both cases, the import script should be able 
> to change the uploaded coordinates accordingly.
>
> J.D. "Dutch" Schmidt
>

With the Isle of Wight and Solent data the only noticeable shift is towards 
to the south, and it seems to be about one second.

David