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

[John Smith]

2010/1/9 Frederik Ramm <frederik at remote.org>:
> * If your editor was using EPSG:4326 then the line you saw on the screen
> *will* go through that point.

Most imagery, if not all, used for this purpose will be EPSG:4326, ie
lat/lon, and the co-ords uploaded to OSM is lat/lon, and ways are a
collection of points, they don't have their own co-ords...

> ... simple two-dimensional line drawing algorithms. Unless you add extra
> tags to the way which tell the renderer how to interpolate between the two
> points, there is not enough information to know.

Why isn't there?

mapnik etc convert from lat/lon to x/y before drawing, so they could
easily add extra x/y points when the conversion process happens.

> Now either we provide that information, by making a rule and hoping everyone
> understands and adheres to it (unlikely), or else we just try and keep our
> nodes close enough to each other because that will then reduce the error
> introduced by the ambiguity discussed above, to something that we do not
> have to care about.

Except for the fact that OSM only accepts lat/lon, the x/y happens
during preprocessing before mapnik gets it, if extra points are needed
the preprocessor can generate them.

> Also, just in case that has not become clear enough already, our "map" API
> call does not catch lines that intersect the bounding box without nodes in
> between, so any editor/renderer relying on this API call will not even get a
> chance to "deal with it" because the software won't even know that there is
> a line to be drawn. This is another reason why keeping your node distances
> in the < 5km range makes a lot of sense.

No it isn't, the preprocessing software could do that if it needs it,
this isn't a reason to add extra nodes to the database.