Re: [OSM-talk] area topology
On Thu, 15 May 2008 08:28:13 +0200 (CEST) "Karl Eichwalder" <[EMAIL PROTECTED]> wrote: > > this is what you say. I say "sharing nodes of the forest and the > > road is actually the correct way to do it." > > In the beginning, I thought the same. Now I keep the node separate. > It is just too cumbersome if you have to separate them later on. I find it more cumbersome to have to search around for all kinds off stuff when I move a road a bit whether there are other things that should be moved too. But I do see your point and understand it. All I am saying is that we need to accept that sometimes there might not be the one universally accepted way to do something *correctly*. Sometimes correctly will have to mean different things to different factions. An neither of these approaches is inferior or superior per se. spaetz ___ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/talk
Re: [OSM-talk] area topology
Sebastian Spaeth schrieb: > this is what you say. I say "sharing nodes of the forest and the road > is actually the correct way to do it." In the beginning, I thought the same. Now I keep the node separate. It is just too cumbersome if you have to separate them later on. And you often have too. At least in Germany, trees more and more are taken apart from the road too minimize all these accidents... -- Karl Eichwalder ___ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/talk
Re: [OSM-talk] area topology
On Tue, 13 May 2008 23:25:39 +0200 Raphaël Jacquot <[EMAIL PROTECTED]> wrote: > the "boundary of the forrest run in parallel to the road" is actually > the correct way to do it. this is what you say. I say "sharing nodes of the forest and the road is actually the correct way to do it." Why can't people accept that sometimes there is simply no agreed correct way of doing things. spaetz ___ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/talk
Re: [OSM-talk] area topology
Stephen Gower wrote: > On Tue, May 13, 2008 at 02:31:32PM +0100, Andrew Chadwick (email lists) wrote: > > A road is represented by a single way. Although the way has zero > width in the database, it represents the whole width of the > carriageway (pavement) and well as the pavement (sidewalk). If a > minor road meets a more important way at a T-junction, we do not > put the last node where the minor road ends, instead we extend it > to the centre of the more important one. The Way in the database is the centre of the real-world carriageway, plus any short extensions necessary to make the routing graph work. Not the same thing as a centreline ;) Representing shape accurately is important to areas. Rendering reachability is more important than shape for roads. There are two classes of object here, each with differing requirements and allowable compromises. > In the same way, if an > area comes right up to the edge of a road (including its pavement, > etc), we should extend the area to use the same defining nodes. I disagree! But you knew that. Let me try to explain more clearly why I think this is wrong. You _don't know_ where the edge of the rendered road will be but that it'll lie within a certain zone. Thus you infect the edge of the abutted area with that uncertainty, and for most buildings, fields, residential areas, or any other Area that doesn't make sense. It's abusing the fact that the renderer will render the road on top of a conjoined area at whatever width the view dictates. It is better to get shape and coverage down correctly for areas, especially buildings. With a system like OSM where one can ignore or disregard some types of object when rendering in favour of others, it's important to map each sort of object accurately *in and of itself*, *in its own terms*, without undue reliance on adjacent objects and the way they get rendered. Contrived example: say you're an arty type or a town planner rendering _just_ the buildings and building-like zones within a city and considering the negative spaces between them for either aesthetic[1] or civil engineering reasons. Abut two buildings to a single road, render without the road "defining" the edge, and suddenly your negative space is zero, buildings are touching, and the rendered map is All Wrong. It is wrong because the data was wrong for the buildings. To think of it all another way, road widths are always scaled to whatever is appropriate for the viewer. Take a look at some other street maps, and you'll see roads seemingly painted with yard brushes because for their readership it's street names and road routes that matters. [1] Yes, it matters *pats his copy of _A Pattern Language_*. -- Andrew Chadwick ___ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/talk
Re: [OSM-talk] area topology
Jannis Achstetter wrote: >Sent: 14 May 2008 8:05 AM >To: talk@openstreetmap.org >Subject: Re: [OSM-talk] area topology > >Stephen Gower schrieb: >> On Tue, May 13, 2008 at 02:31:32PM +0100, Andrew Chadwick (email lists) >wrote: >>> I subscribe to the view that areas should correspond to the real area on >>> the ground and mostly be kept clear of roadways. Placing an Area's Nodes >>> near the adjacent Way's nodes helps make the map easier to maintain. I >>> will often abut adjacent areas that are separated only by something thin >>> and make their nodes share, however. >> >> Putting the other side of the argument, as Andrew I'm sure knew I >> would: >> [...] > >How about buildings that really are at the edge of a road? (No fence, no >space). I'm afraid I can't show you a photo yet. >Do they share nodes since the "buildings are the border of the road" or >don't they share them since "you can't enter the building from any point >of the road"? >(The area I talk about is this one: >http://informationfreeway.org/?lat=49.971764870557124&lon=9.161737364989326 >&zoom=17&layers=B000F000F In this case if highway means the whole of the roadway width including any sidewalk/pavement if applicable (as it generally does in an OSM context) and the house abuts the highway then the two physical objects share the same boundary and hence can be mapped in OSM using common nodes. Where some other physical feature exists between the two objects then they should be separated, unless it's a regular linear feature, in which case the same nodes can also be used for that; a fence for instance. If they are separated by an area, grass for instance, then the highway and building ought not to share nodes. The fact that you cannot enter the building from the highway should be immaterial as we only normally make common paths between common features, although there are one or two logical exceptions to this rule. A slipway into a body of water might be an example. > >and I know the buildings' shapes aren't correct but there are no >Yahoo-Images for the city and I just did a quick run over the campus to >get it mapped basically.) And that is the way it should be. >In this case I didn't share nodes to be able to edit the buildings >without having to change the road every time (and to make the road have >less nodes sind it really is 100% straight). Acceptable. If someone thinks it should be done differently then they are entitled to change to better reflect the physical. Cheers Andy ___ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/talk
Re: [OSM-talk] area topology
Stephen Gower schrieb: On Tue, May 13, 2008 at 02:31:32PM +0100, Andrew Chadwick (email lists) wrote: I subscribe to the view that areas should correspond to the real area on the ground and mostly be kept clear of roadways. Placing an Area's Nodes near the adjacent Way's nodes helps make the map easier to maintain. I will often abut adjacent areas that are separated only by something thin and make their nodes share, however. Putting the other side of the argument, as Andrew I'm sure knew I would: [...] How about buildings that really are at the edge of a road? (No fence, no space). I'm afraid I can't show you a photo yet. Do they share nodes since the "buildings are the border of the road" or don't they share them since "you can't enter the building from any point of the road"? (The area I talk about is this one: http://informationfreeway.org/?lat=49.971764870557124&lon=9.161737364989326&zoom=17&layers=B000F000F and I know the buildings' shapes aren't correct but there are no Yahoo-Images for the city and I just did a quick run over the campus to get it mapped basically.) In this case I didn't share nodes to be able to edit the buildings without having to change the road every time (and to make the road have less nodes sind it really is 100% straight). Jannis smime.p7s Description: S/MIME Cryptographic Signature ___ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/talk
Re: [OSM-talk] area topology
Stephen Hope wrote: > Says who? The boundary of the forest IS the road. :) > > This is one of religious discussions - both sides KNOW they are right, > and no amount of discussion is going to change things. Unless we have > a central decision making force of some sort lay down the law, (in OSM > - hah!) you'll continue to see things mapped both ways. >> the "boundary of the forrest run in parallel to the road" is actually >> the correct way to do it. Yep - BOTH statements are right - but it depends on your context. UNTIL roads actually have width, then the "boundary of the forest runs in parallel to the road" is correct since the road has width beyond it's way, and since around here woodland areas have differing widths of grass verge between the dry stone wall or other boundary and the road surface, then the woodland boundary needs to be a different way to the 'nominal' centre of the road provided by the route way. So even the nodes are not common? With the increasing use of the data FOR micro-mapping - and I include the cycleway maps in that - some means of identifying the real geometry of the road surface is becoming more essential. Forest is going to be in a different position adjacent to a 6 line motorway as against a two lane one, and when laying out pathways inside the forest, a 20 foot wide bridal way/fire break is different to an 18 inch wide footpath. And for orienteering maps THAT detail can be critical - and OSM may be the only way of producing up to date maps for those types of sport? -- Lester Caine - G8HFL - Contact - http://home.lsces.co.uk/lsces/wiki/?page=contact L.S.Caine Electronic Services - http://home.lsces.co.uk EnquirySolve - http://enquirysolve.com/ Model Engineers Digital Workshop - http://medw.co.uk// Firebird - http://www.firebirdsql.org/index.php ___ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/talk
Re: [OSM-talk] area topology
Says who? The boundary of the forest IS the road. :) This is one of religious discussions - both sides KNOW they are right, and no amount of discussion is going to change things. Unless we have a central decision making force of some sort lay down the law, (in OSM - hah!) you'll continue to see things mapped both ways. Stephen 2008/5/14 Raphaël Jacquot <[EMAIL PROTECTED]>: > > the "boundary of the forrest run in parallel to the road" is actually > the correct way to do it. > ___ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/talk
Re: [OSM-talk] area topology
Christoph Eckert wrote: > Hi, > >> The issue is especially contended when it comes to linear features >> straddling areas, like a road that forms the forest boundary for a >> bit. I would re-use the same nodes here, but there are people who say >> that this would indicate the forest stretching up to the road >> centreline which of course isn't true, and they would rather have the >> road and the forest boundary run in parallel and use their own nodes. > > the main issue might be that it's very difficult to maintain/edit such roads. > > Best regards, > the "boundary of the forrest run in parallel to the road" is actually the correct way to do it. ___ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/talk
Re: [OSM-talk] area topology
Hi, > The issue is especially contended when it comes to linear features > straddling areas, like a road that forms the forest boundary for a > bit. I would re-use the same nodes here, but there are people who say > that this would indicate the forest stretching up to the road > centreline which of course isn't true, and they would rather have the > road and the forest boundary run in parallel and use their own nodes. the main issue might be that it's very difficult to maintain/edit such roads. Best regards, ce ___ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/talk
Re: [OSM-talk] area topology
On Tue, May 13, 2008 at 02:31:32PM +0100, Andrew Chadwick (email lists) wrote: > > I subscribe to the view that areas should correspond to the real area on > the ground and mostly be kept clear of roadways. Placing an Area's Nodes > near the adjacent Way's nodes helps make the map easier to maintain. I > will often abut adjacent areas that are separated only by something thin > and make their nodes share, however. Putting the other side of the argument, as Andrew I'm sure knew I would: A road is represented by a single way. Although the way has zero width in the database, it represents the whole width of the carriageway (pavement) and well as the pavement (sidewalk). If a minor road meets a more important way at a T-junction, we do not put the last node where the minor road ends, instead we extend it to the centre of the more important one. In the same way, if an area comes right up to the edge of a road (including its pavement, etc), we should extend the area to use the same defining nodes. If we do not do this, we have an undefined space between the area and the road. This undefined space is of variable width and, without knowing how every renderer is going to treat the highway, there is no way of knowing if it will appear or not, unless it is arterially small (aka 0!). There is some merit to the argument that seperation would help with routing. We could have a convention that if an area is accessible from any point on the highway they should share segments, but if that's not the case (there's a fence between, for example) they should be seperated. While I can see how this would work, it feels like an ugly hack. It's not my itch, but there's got to be a better way of expressing the boundary between highway and area - I guess with a relation. > Rectilinear buildings in particular should be kept rectilinear: there's > no excuse for trapezoidal buildings with the new extrusion stuff now in > JOSM :) I agree with that as a potential stumbling block, and was concerned about this until I actually started mapping buildings. In practice, the resolution of accuracy in OSM is such that you can make a fair representation of the shape of the building and still share nodes with the highway it abuts. > However, rivers are Interesting: quite often an Area whose edge is > defined by a river may change over time as the river meanders... In that > case, it probably does make sense to abut a Way to an Area. It should be noted that roads also change position sometimes, affecting the areas that are defined by them!. s ___ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/talk
Re: [OSM-talk] area topology
Shaun McDonald wrote: > If you have a road and stream running parallel they would be entered > as 2 ways that are parallel. The same happens for the carriageways of > a motorway that are separated by a barrier. Well, let's say that this is also controversial and we had that discussion before. Personally I use sharing nodes when I have a forest that borders on a motorway, for example. So, there might not be the one solution for all. Either parallel ways that are next to each other or share nodes... spaetz ___ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/talk
Re: [OSM-talk] area topology
Hi, > Am I right in assuming that OSM ways always belong > to one single area? Yes and no. Normally we don't map the borders between areas - we map tha areas themselves. So you would have one way that encloses the forest, and one way that encloses the adjacent farmland, and they would "meet" somewhere. There are exceptions to this rule when it comes to very large entities like counties or countries; in these cases we tend to actually map the border line and tag it with something like "left: France, right: Germany", and there will be no single polygon named "France" or "Germany". Coastline is another exception. > If this is so, do I have to duplicate ways along the > common border? JOSM informs about double ways when it validates > data so > I had the slight impression that they are not really wanted. There is no 100% consensus on how to deal with these things but most people, including me, suggest to duplicate ways (not nodes) along the common border, i.e. you will have two ways sharing the same nodes. The issue is especially contended when it comes to linear features straddling areas, like a road that forms the forest boundary for a bit. I would re-use the same nodes here, but there are people who say that this would indicate the forest stretching up to the road centreline which of course isn't true, and they would rather have the road and the forest boundary run in parallel and use their own nodes. Bye Frederik -- Frederik Ramm ## eMail [EMAIL PROTECTED] ## N49°00'09" E008°23'33" ___ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/talk
Re: [OSM-talk] area topology
On 13 May 2008, at 14:06, Ulf Mehlig wrote: > Please excuse me if this is a FAQ, I just didn't find an answer in the > wiki (possibly because it is obvious) ... > > In topological GISses like grass, borders are shared between adjacent > (vector) areas. However, I wonder how adjacent areas should be > digitized > in OSM (let's say, forests and farmland, or riverbanks and the > associated wetlands). Am I right in assuming that OSM ways always > belong > to one single area? If this is so, do I have to duplicate ways along > the > common border? JOSM informs about double ways when it validates data > so > I had the slight impression that they are not really wanted. > > I see a similar problem with line data (e.g. roads, streams) which may > happen to be an area border. From reading > > http://wiki.openstreetmap.org/index.php/Editing_Standards_and_Conventions#Tagging_Areas > > I think that using a street as a border of a plaza (or a block of > buildings) is not wanted. Does one digitize double ways, leading along > the same nodes, or does one make a separate area in a small distance > to > the existing line (street/stream), which might be topologically > incorrect and is more difficult to maintain? > If you have a road and stream running parallel they would be entered as 2 ways that are parallel. The same happens for the carriageways of a motorway that are separated by a barrier. The way that I look at it, is if there is a barrier, such as a fence of wall, then the node in the way should not be shared. Otherwise the sharing of nodes isn't a problem, and can produce better results, especially for routing. Shaun ___ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/talk
Re: [OSM-talk] area topology
Ulf Mehlig wrote: > I think that using a street as a border of a plaza (or a block of > buildings) is not wanted. Does one digitize double ways, leading along > the same nodes, or does one make a separate area in a small distance to > the existing line (street/stream), which might be topologically > incorrect and is more difficult to maintain? There are arguments both ways, and it's come up in discussion locally: http://wiki.openstreetmap.org/index.php/Talk:Oxford#How_much_separation_is_right.3F I subscribe to the view that areas should correspond to the real area on the ground and mostly be kept clear of roadways. Placing an Area's Nodes near the adjacent Way's nodes helps make the map easier to maintain. I will often abut adjacent areas that are separated only by something thin and make their nodes share, however. Rectilinear buildings in particular should be kept rectilinear: there's no excuse for trapezoidal buildings with the new extrusion stuff now in JOSM :) However, rivers are Interesting: quite often an Area whose edge is defined by a river may change over time as the river meanders... In that case, it probably does make sense to abut a Way to an Area. -- Andrew Chadwick ___ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/talk
