[Talk-ca] Using Canvec data to recreate or modify coastline features

James A. Treacy treacy at debian.org
Tue Sep 13 04:14:00 BST 2011


Thanks for the confirmation Daniel. Now I've got to go back over a
rather large area to make sure it is all correct.

On Mon, Sep 12, 2011 at 10:13:50PM -0400, Daniel Begin wrote:
> Bonjour James, sorry for the delay.
> 
> About your example, I couldn't have shown it better!
> 
> The procedure I use ...
> - All features having a natural=water tag are dissolved together before
> creating a coastline feature.
> 
> - The features having natural=water and water=intermittent tags are copied
> into another layer before being reintegrated after the creation of the
> coastline feature. 
> 
> Daniel
> 
> -----Original Message-----
> From: James A. Treacy [mailto:treacy at debian.org] 
> Sent: September-08-11 13:59
> To: Daniel Begin
> Cc: talk-ca at openstreetmap.org
> Subject: Re: [Talk-ca] Using Canvec data to recreate or modify coastline
> features
> 
> Daniel,
> I'd like to make this more concrete with an example. If you have canvec data
> that shows:
>       llllllllllll      this area is land
>     -i-i-i-i-i-i-i-i    way which is natural=water;water=intermittent
>       iiiiiiiiiiii      area with intermittent water
>     -w-i-w-i-w-i-w-i    boundary with 2 ways. One is natural=water and
>                             the other is natural=water;water=intermittent
>       wwwwwwwwwwww      this area is water
> 
> is this what OSM should have?
>       llllllllllll      this area is land
>     -c-i-c-i-c-i-c-i    boundary with 2 ways. One is natural=coastline and
>                             the other is natural=water;water=intermittent
>       iiiiiiiiiiii      area with intermittent water
>     -i-i-i-i-i-i-i-i    way which is natural=water;water=intermittent
>       wwwwwwwwwwww      this area is water
> 
> Obviously, the ways would be closed but I think this gives the idea.
> 
> On Mon, Sep 05, 2011 at 09:37:11PM -0400, Daniel Begin wrote:
> > Hi all,
> > 
> > Earlier today I was looking at coastline features modified to fit Canvec
> > data and I found a problem with the "conversion". I think all of those who
> > are converting coastline using Canvec data should be aware of the Canvec
> > water data model...
> > 
> > In Canvec data you will find two types of water polygons
> (natural=water)...
> > 
> > One type defines permanent water - an area that is always covered by the
> > water. 
> > 
> > - It is tagged natural=water
> > 
> > One type defines intermittent water - an area that is occasionally, but
> not
> > always covered with water.
> > 
> > - It has two tags. One is the standard natural=water tag, the other is
> > water=intermittent tag(1).
> > 
> >  
> > 
> > The problem is that the coastline seems to be defined as the mean high
> water
> > level (MHWL) position(2). To create a coastline that meet the MHWL
> position
> > using Canvec, you must merge all natural=water polygon type before
> > converting it to coastline.
> > 
> >  
> > 
> > JOSM provides a good tool to merge those polygons - join overlapping area
> > (Shift-J)
> > 
> >  
> > 
> >  
> > 
> > Daniel
> > 
> >  
> > 
> >  
> > 
> >  
> > 
> > 1 - http://wiki.openstreetmap.org/wiki/Proposed_features/Water_cover
> > 
> > 2 - http://wiki.openstreetmap.org/wiki/Tag:natural%3Dcoastline and other
> > wiki discussions
> > 
> 
> > _______________________________________________
> > Talk-ca mailing list
> > Talk-ca at openstreetmap.org
> > http://lists.openstreetmap.org/listinfo/talk-ca
> 
> 
> -- 
> James (Jay) Treacy
> treacy at debian.org

-- 
James (Jay) Treacy
treacy at debian.org



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