[Talk-GB] Ordnance Survey 7th series available

Andy Robinson (blackadder-lists) ajrlists at googlemail.com
Wed Oct 7 12:28:07 BST 2009


Which NPE WMS are you using. Is it by any change the "nick" version on dev?
I get a much better alignment for that area with the re-rectified NPE tiles
from TimSC's space at http://dev.openstreetmap.org/~timsc/wms2/map.php?



>-----Original Message-----
>From: David Earl [mailto:david at frankieandshadow.com]
>Sent: 07 October 2009 11:23 AM
>To: Andy Robinson (blackadder-lists)
>Cc: 'Steve Chilton'; 'Shaun McDonald'; 'Frankie Roberto'; talk-
>gb at openstreetmap.org
>Subject: Re: [Talk-GB] Ordnance Survey 7th series available
>NPE maps have always had major alignment problems which have seemed to
>me to be worse in the eastern side of the country. There's also a new
>problem, but I don't know whether it is in the JOSM WMS plugin, the tile
>server or what.
>Consider three JOSM screenshots:
>The first is Landsat, obviously. It defaults with an offset of about
>100m vertically and horizontally in my part of the world (52N 0E) as can
>be seen from the obvious course of the road on the satellite images at
>the orange arrows. But once the layer is aligned on known points, it
>tends to be aligned across the whole working area.
>NPE maps in contrast, in the second one, firstly has a relative
>displacement of tiles (about 150m) in JOSM which is obvious in this
>unadjusted download. (We also have to add to that that the map sheet
>boundaries don't line up anywhere near accurately)
>The third one though shows that even within a single tile, the alignment
>drifts extremely rapidly. I aligned the third one with the junction at
>point 1 near the top left of a tile, and you can see that at the bottom
>right of the tile, the bend I've marked is off by about 150m
>horizontally and 115m vertically over a distance of about 1500m - 10%.
>All the roads in this area are GPS surveyed (I did them).
>I mentioned this when NPE maps first arrived, but it's never been
>addressed. Is it a rectification problem, or a problem of how JOSM or
>the WMS plugin scales or displays the tiles?
>The tile displacement problem is recent and I'm sure that will easily be
>fixed. The variation across a tile is more awkward I think.

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