[OSM-talk] New "Highways" view in OSM Inspector

[Greg Troxel]

  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.


I think we are in state 6, but it would be good to have a formal
definition.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 194 bytes
Desc: not available
URL: <http://lists.openstreetmap.org/pipermail/talk/attachments/20100109/90d9fe99/attachment.pgp>