Rendering will always be an imperfect representation of the real world. I still feel that there is an inconsistency with the way these two circumstances are handled, but understand that this is one of the non-open parts of Open Street Map. I'm done trying to swim upstream on this.
On Fri, Mar 2, 2018 at 7:17 AM, Volker Schmidt <vosc...@gmail.com> wrote: > The layers tag in OSM is only to enable the renderer to display/draw > crossing OSM elements correctly. The element with the higher layer value is > drown over the ones with lower layer values. > > In the case of the ford the waterway and the highway are on the same layer > and share a node, which represents the ford (assuming that highway and > waterway are line objects. If the waterway and/or the highway are drawn as > polygons, then the ford becomes a line or a polygon.) > > In case of a culvert the objects are not on the same layer. The highway is > above the waterway (which may be intermittent or a wadi). Hence a common > node is not correct. You could argue that the culvert becomes a node on the > lower way, that is not connected with the highway above. It would have to > be drawn exactly on the crossing point, without being part of the highway > above. A non-zero length culvert is most likely easier to draw, and also > closer to reality. > Again, when the waterway is drawn as a Polygon, the culvert becomes a > polygon. > > On 2 March 2018 at 15:41, Vao Matua <vaoma...@gmail.com> wrote: > >> Thank you Ralph, I understand your perspective, but have to disagree a >> bit (I'm not looking for a battle, however). >> >> A ford is a stack of layers that are directly adjacent vertically, with >> the road slightly below the stream/river. In the dry season a ford is only >> a road and only becomes a ford when a watercourse flows over the top of the >> road. >> >> A culvert is a part of of road construction, a culvert would not exist >> without the road, but the culvert is utilized by the stream. Personally I >> have physically installed culverts in road profiles where there is no >> watercourse. If I try to add a culvert in JOSM without an additional tag I >> get a validation warning. >> >> Wouldn't a road/stream crossing without a culvert or bridge be called a >> dam? >> >> Isn't a culvert similar in rendering to an embankment? An embankment is >> a tag applied to a road or railroad, but it is a level beneath the road or >> railroad. A culvert happens to be perpendicular or so to the road rather >> than adjacent to it. >> >> Part of this discussion also is a matter of scale. At some rendering of >> a map even a place like Paris would be displayed as a node. In the same >> way a culvert displayed as a node would be appropriate at certain zoom >> levels. >> >> I think an easy solution is to make the rendering rule for culverts be a >> layer below the road and allowed to be a node. >> >> I think this is an interesting discussion and is helping me understand >> different points of view, thanks. >> >> Emmor >> >> On Fri, Mar 2, 2018 at 12:39 AM, Ralph Aytoun <ralph.ayt...@ntlworld.com> >> wrote: >> >>> The real easy way to understand *culverts* and *fords* for >>> OpenStreetMap is about the layers they are on and this dictates the nodes >>> they use. >>> >>> >>> >>> For a *ford* the stream/river is at the same level as the road >>> (effectively *layer=0*) and therefore they are able to share a node. >>> >>> >>> >>> Because a culvert (*layer=-1*) is not on the same level as the road >>> but passes underneath so it cannot share a node with the road and therefore >>> the culvert is attributed to the river/stream with a node either side of >>> the road. >>> >>> >>> >>> With a *bridge* the road (*layer 1*) is not on the same level with the >>> stream/river so again cannot share a node and therefore the bridge is >>> attributed to the road with a node at each end of the bridge. >>> >>> >>> >>> Hope this will be of help in understanding the problem. >>> >>> >>> >>> >>> >>> Sent from Mail <https://go.microsoft.com/fwlink/?LinkId=550986> for >>> Windows 10 >>> >>> >>> >> >> >> _______________________________________________ >> Tagging mailing list >> Tagging@openstreetmap.org >> https://lists.openstreetmap.org/listinfo/tagging >> >> > > _______________________________________________ > Tagging mailing list > Tagging@openstreetmap.org > https://lists.openstreetmap.org/listinfo/tagging > >
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