On Sat, Mar 29, 2008 at 3:14 PM, MilesTogoe <[EMAIL PROTECTED]> wrote: > Frederik Ramm wrote: > > Hi, > >> I was thinking about adding nodes to long ways. This may sound a bit > >> ugly at first, but not if you consider the fact that the SRTM actually > >> provides real information about these points along long ways. It is > >> just that the latitude and longitude are not reliable, only the > >> altitude is. > >> > > > > Doesn't sound very good to me, adding nodes to existing ways just to > > import height... I'd rather have the height as a separate info. Much > > like a road that enters a forest; I don't put a node at that point > > just to say that this node represents the road entering the forest - I > > just model the forest as an extra entity and whoever needs to can > > compute the point. > > > > Also, having SRTM data as nodes in OSM touches on the often discussed > > topic of immutable data. Would it be ok for people to edit individual > > SRTM nodes? > > > > I'd also recommend to first do an analysis about the impact on OSM > > altogether, i.e. by how much would the planet file grow by importing > > SRTM data like you suggest? If renderers would start to use that > > information, then we'd suddenly have not a single "empty" tile > > anymore, every land tile on the planet would have information on it > > (right?), how would taht impact storage requirements for tile servers > > etc.? - Not saying that any of these could be a show-stopper, it's > > just that such an analysis should be part of the plan. > > > Actually the vertical inflection points (bottom, change, or top of > vertical curve) along a way are very useful points to have even if they > are along a tangent section. The inflection points are used for sight > distance, drainage issues, calculation of grade or steepness, > calculation of traveled distance, etc. Each node and inflection point > should have the lat, long, and elevation. A straight line but up and > down way will have a greater travel distance than a flat way. As a > civil engineer, I've always thought 2-D points are lacking and should > always be 3-D points. Is it more storage, processing/retrieval cost ? > Sure, but it's important data.
I agree with Frederik that the SRTM nodes might not be a good idea, because they should then be immutable. I tend to agree with Miles here on the need to have 3-D in stead of 2-D nodes. My current understanding of nodes is that they represent *where* something is, not *what* it is. In that case I would argue that the altitude is part of 'where' and whether it is a forest is part of *what*. In that case altitude should be part of the node and forest should be a tag. I am also thinking about cities here; you can have two subways, a road and a bridge at one lat & lon position. If altitude is not a seperate layer of information, but part of the nodes that make up these subways and roads, there is no problem here. I also agree with Frederik about analyzing the potential impact of different approaches. So I will include such an analysis in the proposal and somewhere during the project we will have this discussion again with some numbers and examples so support it. Kind regards, Sjors _______________________________________________ dev mailing list [email protected] http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/dev
