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

[Anthony]

On Sat, Jan 9, 2010 at 10:50 AM, Patrick Kilian <osm at petschge.de> wrote:

> Hi all,
>
> > And, thinking about it a bit, I guess the proper rule is that (10,
> > 10) -> (30, 30) passes through (20, 20), since it's completely
> > unrealistic to assume that the basic renderers will do otherwise.
> And this is where you are wrong. On zoomlevel 0 (one tile for the whole
> earth) (10,10) ends up on (135.11, 135.15) and (30,30) ends up on
> (149.33, 150.38).
>

Thanks for this.  I'll have to look into it further.


> > And what that also means is that a straight line on earth which is
> > more than a certain length is not properly represented by a way with
> > two points.
> THAT depends on your definition of "straight line".
>

I suppose, but it'd have to be a pretty contrived definition of "straight
line" to be equivalent to Spherical Mercator, would it not?

> One thing I can't quite get my mind wrapped around is whether or not
> > a geodesic is what we'd call a straight line on the earth.  If we put
> >  a few million (?) rulers end-to-end as best we could, would that
> > form a geodesic, and if not, what would it form?  I'm fairly certain
> > it wouldn't pass (10, 10) -> (30, 30) through (20, 20), since 20
> > degrees of longitude does not (generally) equal 20 degrees of
> > latitude in length. But I'm not sure if it'd be a geodesic or not.
> > I'd love for someone to answer that question and provide a link or
> > source to back up their answer.
> Well. There isn't one single definition of "straight line" here.


Right.  My definition, for the purpose of the mind experiment, was the thing
I'd get if I placed a bunch of rulers end to end as best as I could.

The answer might be "what you end up with depends on which errors you make
when trying [and failing] at placing the rulers end to end".  I don't know.

Another mind experiment would be to question what I would get if I placed a
bunch of rulers end to end and connected them with hinges so that they could
bend vertically but not horizontally.  I think that's what's meant by
"straight" when we call a road "straight".  May or may not be equivalent to
"the shortest distance between two points using a path which lies on the
surface of the earth".  If I had to guess (and it'd be a fairly random guess
relying solely on what I remember from when I held a string up to a globe),
I'd say the two lines wouldn't coincide.

So don't stop assuming that is a
> simple topic, everybody was just a lazy bum or that you know it all (tm).
>

Never assumed any of that.  Just the opposite, in fact.  It's not a simple
topic, and I don't know it all - that's exactly why I'm posting on this
list.

And not everyone is a lazy bum.
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