An other practical alternative: Leave the exact definition of line segments undefined (as Frederik suggests). Then tag "straight" ways as "straight"="great circle" or "straight"="lattitude" or what ever. And then tag the redundant nodes as "redundant"="yes".
Egil Egil Hjelmeland wrote: > Egil Hjelmeland wrote: > Sorry, I forgot to change the subject line. >> I think it does not hurt to define the exact meaning of a >> line-segment in OSM. And I think that great circle (in wgs84) is the >> natural choice, in stead of defining line to be straight relative to >> some arbitrary projection. >> >> Since the API (for performance reasons) can not return line segments >> with endpoint outside the bounding box, we (at least for some time) >> have to live with adding redundant nodes for every x km for >> great-circle lines. Then I suggest that the purists may add a tag >> "redundant"="y" to the redundant nodes. >> >> To Frederik's concern about mappers getting confused about what a >> straight line is: I guess that there is only a tiny fraction of the >> mappers that ever will come across very long line segments. I suppose >> more than half of them can do it right in the first place if it is >> properly described on the Wiki. (Particulary state that a line of >> lattitude is not a Great circle, except for equator). And the other >> cases can be corrected by others who understands the concept of a >> great circle. That is the beauty of wiki-style mapping. >> >> Best regards >> Egil >> >> >>> Message: 6 >>> Date: Sat, 09 Jan 2010 09:58:20 -0500 >>> From: Greg Troxel <g...@ir.bbn.com> >>> Subject: Re: [OSM-talk] New "Highways" view in OSM Inspector >>> To: Frederik Ramm <frede...@remote.org> >>> Cc: OSM Talk <talk@openstreetmap.org> >>> Message-ID: <rmiskafl3zn....@fnord.ir.bbn.com> >>> Content-Type: text/plain; charset="us-ascii" >>> >>> >>> We were discussing what exactly a straight line was. There is no >>> such thing as a "straight line in the database", because, as you >>> correctly state, the database only stores the end points of a >>> line. If you draw a line from point lat=10;lon=10 to >>> lat=30;lon=30, then it is unclear whether that line visits point >>> lat=20;lon=20. Some might think yes, some might think no. >>> >>> I think this is exactly the key question. >>> >>> When there is a line segment in the database, in WGS84 lat/lon, with >>> points (lon1,lat1) and (lon2,lat2), then we need to have a >>> definition of >>> what that representation means. Obvious candidates are: >>> >>> 1) linear in lon,lat space >>> >>> 2) great circle in wgs84 >>> >>> 3) linear in google spherical mercator >>> >>> 4) linear in WGS84 UTM >>> >>> 5) linear in your own country's local grid, or US state plane >>> coordinate >>> system >>> >>> 6) we don't define it, and if any of the above are different in any >>> discernible way, you need more points. In the 10,10 30,30 example >>> above, we are clearly in this state. >>> >>> >>> >> >> > > _______________________________________________ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk
