[Talk-ca] Canvec import issues

Wed Aug 22 16:59:41 BST 2012

Hi Daniel, Pierre,

It is possible to reuse ways in the OSM datamodel, as you know. It is 
also possible to do this, while having to make extracts later. For 
example, when you only want to select lakes, you should do the following 
in JOSM:
* Select natural=water, replace selection
* Select child selected, add to selection
This way you have all lakes, including multipolygon ones with islands. 
Note that the islands could have tags applied on them as well. You can 
deal with them after you've copied the data to another layer.

Anyways, unfortunately it is not possible to have ways being reused 
easily with JOSM. At least not with standard JOSM or the Validator tool. 
Perhaps there is a plug-in. I haven't looked into that. However, if this 
functionality were to be implemented, it could easily open a new can of 
worms. Sometimes it also happens that functionality is revised (wholly 
or partially). For example, that is the case with "unclosed ways". Now 
it isn't possible to merge duplicate nodes with the Validator tool. With 
all the crossing address interpolation ways and streams, I need to merge 
them manually tens of times per sheet, sometimes even up to a hundred 
times. (Probably not much more, because sheets are being split up 
farther in crowded, residential areas.)

History also shows that everyone has his own standards, even amongst all 
the people who have imported Canvec data. However, that is an entirely 
different discussion...

Frank

On 21-8-2012 22:49, Daniel Begin wrote:
>
> Bonjour Pierre,
>
> The Canvec Geometric Model is explained in the following OSM wiki page ...
>
> http://wiki.openstreetmap.org/wiki/CanVec:_Geometric_Model
>
> The model was adopted after discussions with the community. The model 
> was designed to simplify the import of a selection of features by the  
> contributors, instead of imposing import the entire contents by them.
>
> However, history now shows that the community usually imports the 
> entire content.
>
> Compromises always bring pros and cons.!-)
>
> Best regards,
>
> Daniel
>
> ------------------------------------------------------------------------
>
> *From:*Pierre Béland [mailto:infosbelas-gps at yahoo.fr]
> *Sent:* August-21-12 16:04
> *To:* talk-ca at openstreetmap.org
> *Subject:* Re: [Talk-ca] Canvec import issues
>
> I didn't do Canvec imports too much. Looking at various lakes in 
> wooded areas,  I now realize that Canvec imports are often (always?) 
> duplicating lakes. I do'nt know what was the reason to create these 
> duplicate ways in the Canvec import file.  Should we duplicate the 
> lakes to apply a inner role in the relation? Is this a reason for 
> that? Or could we instead simply use the existing lake with a inner 
> role in the wooded area polygon relation?
>
> */Pierre/**//*
>
> ------------------------------------------------------------------------
>
> *De :*Frank Steggink <steggink at steggink.org>
> *À :* talk-ca at openstreetmap.org
> *Envoyé le :* Mardi 21 août 2012 13h32
> *Objet :* [Talk-ca] Canvec import issues
>
>
> Hi,
>
> Today I was contacted by someone inquiring (with a somewhat hostile 
> tone) after the Canvec import I've done over the weekend northwest of 
> Montréal. He was not really happy with the way how the import has 
> handled. The way the Canvec data is currently provided, leaves some 
> room for improvement. I'm not sure if all his issues have been 
> discussed in the past (since I haven't followed all Canvec 
> discussions, especially in the beginning), but I could see some merit 
> in some of the point.
>
> Some examples he provided come from the Mt. Tremblant area [1]. Note 
> that the lakes (and most of the streams) were imported previously by 
> someone else, based on NHN data, but the same issue plays with the 
> Canvec data itself. (This left me to the task to leave the Canvec 
> lakes out of the upload, as well as most streams.)
>
> On the left you see Lac Ouimet. He mentioned that a large part of the 
> ways are duplicated. The outer boundary of the wooded area is a 
> separate polygon from the lake itself.  However, Lac Gauthier on the 
> right is a different case. This lake has been "cut out" from the 
> woods, and I left the inner boundary intact. JOSM is not complaining 
> about this. Since dealing with multipolygons remains a sticky issue, I 
> have not done that. I think it would be better to take care of these 
> issues with some tool. Although using a tool is considered 
> "dangerously" (and rightfully so!), dealing with multipolygons is 
> prone to errors as well.
>
> Another issue is that some lakes do not have names, but contain a 
> separate node (not part of any of the ways) with natural=water and 
> name=* tags. I can only assume that this comes from the source data. 
> In many cases it is hard to determine the extent of the lake, since it 
> can gradually taper into a river. This was not mentioned directly by 
> the user, but I thought he was referring to this.
>
> His issue turned out to be somewhat different. There is a place node 
> near Lac Gauthier, with the same name. I explained to this that this 
> must be the name of a hamlet. The non-official tag "place=locality" is 
> probably due to this confusion. This name is also visible on the 
> original topo map [2].
>
> Furthermore he noticed that I have duplicated his address nodes and 
> ways. This was an omission, so I have corrected this. I scan the 
> existing data in order not to duplicate existing features. Of course 
> this is prone to errors as well, especially in a large area which is 
> void of address nodes and ways, except for two ways around a lake...
>
> I'm not asking anyone for "solutions". I can easily think about them 
> as well, but that doesn't make the problem go away. Thinking about the 
> solution is the easiest part, but working it out and implementing it 
> is much more difficult. It is more than simply typing in some code and 
> then run it over the data. Instead of doing that, I have tried to 
> explain him something about the hybrid data model OSM is using (not 
> purely geographical, but also not purely topological). And of course 
> there is also the gap between idealists and realists. I see the 
> current state of OSM as the status quo, so I take it for granted. I 
> think that Canvec falls within that status quo situation as well, 
> otherwise the OSM data offered by NRCan would have looked differently, 
> after all those years of discussions and reviews.
>
> I have invited this user to discuss the issues he found on talk-ca. I 
> think that would be much more constructive than having him directing 
> all those issues to me, since they occur far beyond his own backyard 
> as well...
>
> Regards,
>
> Frank
>
>
> [1] 
> http://www.openstreetmap.org/?lat=46.1749&lon=-74.5535&zoom=14&layers=M
> [2] 
> ftp://ftp2.cits.rncan.gc.ca/pub/canmatrix2/50k_tif/031/j/canmatrix2_031j02_tif.zip
>
>
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