Hi Mike, Can you provide us with a grid ref(s) for a location where the OS data is wrong
Jason On 9 March 2011 13:33, Michael Collinson <[email protected]> wrote: > At 13:29 09/03/2011, Chris Hill wrote: > >> On 09/03/11 11:57, Michael Collinson wrote: >> >>> At 12:32 10/02/2011, Andy Robinson (blackadder-lists) wrote: >>> >>>> Henry Gomersall [mailto:[email protected]] wrote: >>>> >Sent: 10 February 2011 11:07 AM >>>> >To: Peter Miller >>>> >Cc: Talk GB >>>> >Subject: Re: [Talk-GB] Incorrect use of OS VectorMap District when >>>> mapping? >>>> > >>>> >On Thu, 2011-02-10 at 10:30 +0000, Peter Miller wrote: >>>> >> On reflection possibly we should use river-bank as that has more >>>> >> information in it, but recommend that anyone importing does a 'bridge >>>> >> cleanup' at the same time. >>>> > >>>> >This is an area I'm actually really interested in (for rural rivers) >>>> and >>>> keen to >>>> >contribute. So far I've been put off by exactly this problem. Is a >>>> reasonable >>>> >approach to use the OS data for river edges and then fill in the gaps >>>> (bridges >>>> >etc) with OSM data? >>>> >>>> +1 >>>> >>>> If the OS vector data is only assumed to be the banks and the additional >>>> data for flow direction, bridges and other features are added from >>>> survey/BING etc then we should end up with a very functional dataset. >>>> >>> >>> A late response to this thread, but a word of caution. Comparing Bing >>> imagery recently for several Yorkshire rivers with folk's riverbanks derived >>> from OS data indicates that very frequently the OS are not tracing the >>> riverbank as the dividing line between water (clear river channel) and land >>> (grass, scrub) but the top of the riverbank or where the rough "verge" meets >>> pasture land. >>> >> A further word of caution: Bing and all other imagery only shows a >> snapshot of the way things are, often many years ago, and in an >> indeterminate state of water level. Some rivers have tidal influences, some >> rivers have very different levels in flood or drought. Sometimes where the >> rough "verge" meets pasture land is the highest point the water reaches >> regularly, but still only occasionally. >> > > Certainly both Chris' and Phillip's cautions are certainly true but I've > paid particular attention to the River Wharfe mid-reaches, which I know very > well and flows in a well-defined channel with high banks and has not > shifted markedly in the last 40 years. In places, it is almost twice as wide > as it should be. Chris may be right in suggesting that the highest water > mark is being mapped, but why map the 10 - 25-year flood event level rather > than the natural bank line? I am tempted to think that automated software > has been used which like PGS coastlines occasionally gets confused by nearby > lineaments. I also recall comparing with digitised 25:000 maps (vintage 1900 > - 1960 surveying) and noticing that it correlates much more closely with > Bing than StreetView. Needs more analysis but be aware! > > Mike > > > > > _______________________________________________ > Talk-GB mailing list > [email protected] > http://lists.openstreetmap.org/listinfo/talk-gb >
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