Frederik and all, Is there now a distinct description on the OSM Wiki, how polygons are defined in OSM? (e.g. self-intersections allowed? inner holes?)
And: Outer boundaries seem to be encoded simply by the fact that first and last point have the same coordinates(?). But how are inner boundaries 'officially' encoded? -- S. 2008/3/17 Andy Robinson (blackadder) <[EMAIL PROTECTED]>: > Andy Allan [mailto:[EMAIL PROTECTED] > >Sent: 17 March 2008 4:20 PM > >To: Andy Robinson (blackadder) > >Cc: Robert (Jamie) Munro; dev > >Subject: Re: [OSM-dev] Advice sought on polygon-with-hole drawing > > > >On Mon, Mar 17, 2008 at 2:28 PM, Andy Robinson (blackadder) > ><[EMAIL PROTECTED]> wrote: > > > >> >Direction is important for one-way roads but shoudn't be for areas. > >> >Coastline is an understandable exception. > >> > >> And even that's easy for a user to swap around without realising the > >affect. > > > >Indeed. > > > >> In reality though, since it's a wiki, when an error is spotted it gets > >> corrected, so we could take the same view with areas, if it renders > the > >> wrong way around its going to get fixed pretty quickly. > > > >Hmm. If there's a 50/50 chance of any car-park doing a planet-span, I > >don't think we'll ever see the map again :-) > > > > I see your concern. > > >> A new user is > >> probably going to find it a lot easier to understand that an area has > to > >> point in the clockwise direction than to have to add some complicated > >> tagging to non closing areas to render properly, so for this approach > I > >> don't feel its too much to ask. > > > >Perhaps more complicated things will require more complicated rules, > >but I really think we should avoid requiring direction for > >non-directional features as much as possible. Inner/outer sounds much > >easier to understand to me than alternating directions, since the > >former is an intrinsic feature of the real-world object where the > >latter is just a consequence of our data model. > > > >> For closed areas then it will always be > >> possible to overrule if the rendering engine so decides. > > > >Which it'll have to do to avoid planet-spans. So if all renders *must* > >ignore way orientation for 3-node areas, then there's no > >right-hand-rule for this case at all and any claims to the contrary > >are a waste of time and energy to the mappers. Unless we want to be > >strict on our inputs (no planet-spanning areas permitted, so no > >anti-clockwise 3-node areas) and therefore overcomplicate the API, or > >make every editor and bulk-uploader strictly follow the convention, we > >may as well let the renders ignore the direction for this case. > > > >Again, perhaps it'll need to be more complicated for the more complex > >situations, but I want to nip in the bud any idea that basic areas > >must have a clockwise orientation. > > > > Agreed. I was more concerned with opening the ability to render more > complex > and larger areas like we deal with coastlines, but you are right, they > should be special cases rather than the norm. > > Cheers Andy > > >Cheers, > >Andy > > > >> Cheers > >> > >> Andy > >> > >> > >> > >> > > >> >Cheers, > >> >Andy > >> > > >> >> It's simple, it's validatable (albeit the current JOSM validator > >get's > >> >> it wrong), it means that coastline is not an exception, it makes > the > >> >> maths simpler. It might even mean that you don't need > relationships > >to > >> >> associate inner and outer - Any system that gets 1 segment of an > >area > >> >> should be able to know which side of that segment the feature is > on. > >> >> > >> >> > >> >> | Also, my idea would allow a way to serve as an "inner" member of > >one > >> >> | multipoly at the same time as as an "outer" member of another; I > >think > >> >> | you couldn't get that with evenodd. > >> >> > >> >> That's really ugly. There should be 2 ways. They can share nodes > if > >that > >> >> ~ is wanted. If you really want to use only one way, then you > could > >put > >> >a > >> >> direction=-1 tag or something in the relationship that defines the > >> >> tagging for the inner area, but I still don't like that. I think > >that if > >> >> the edge of an area crosses through something you should know what > >is on > >> >> each side of it without having to consider special tags for > >exceptional > >> >> cases. > >> >> > >> >> > >> >> Robert (Jamie) Munro > >> >> -----BEGIN PGP SIGNATURE----- > >> >> Version: GnuPG v1.4.6 (Darwin) > >> >> Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org > >> >> > >> >> iD8DBQFH2lboz+aYVHdncI0RAgafAKCJBEW2LG9F6Rczm4gp+EU8/8Qt+gCgpMqE > >> >> M1p5oF0jvynuW31P8KNnu7o= > >> >> =c5+U > >> >> -----END PGP SIGNATURE----- > >> >> > >> >> > >> >> > >> >> _______________________________________________ > >> >> dev mailing list > >> >> [email protected] > >> >> http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/dev > >> >> > >> > > >> >_______________________________________________ > >> >dev mailing list > >> >[email protected] > >> >http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/dev > >> > >> > > > _______________________________________________ > dev mailing list > [email protected] > http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/dev >
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