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

[Martin Siegel]

Am 09.01.2010 01:27, schrieb Dave F.:
> Martin Koppenhoefer wrote:
>    
>> still you are ignoring projection and earth form, or are you talking
>> about a tunnel (you will have to dig into the earth to get a straight
>> line or decent length)?
>>      
> I'm aware of the concept that the earth is not flat.
>
> But... This is a two dimensional map. IFAIK there is no 3d data. The PoV
> of viewing the OSM data via the likes of Mapnik is always through the
> surface of the earth to the centre of the earth. Therefore a line such
> as this Oz highway is, when viewed in a map, going to be straight.
>    
AFAIK this is not correct. First of all the PoV of Mercator projection 
is not going through the center of the earth. It's a somehow stretched 
cylindrical projection and it goes through the north-south-axis.
The way it is stretched causes that angles on the earth are the same as 
on the map. I'm not completely sure, but I believe the only straight 
lines that correlate between earth's surface and Mercator projected maps 
are the equator and all great circles parallel to the meridians.

Greatings: Martin Siegel