[OSM-talk] Datums again?

[Andrew Rowbottom]

in response to

>Can anyone explain why a simple spheric model is not sufficient?
>Does it result in cracks somewhere on the planet?
>Are lat and lon coordinates incorrect for someone's street somewhere?
>Is the distance between two points distorted in some way?

Q1 I'm not answering this one (cop out!)
Q2 It's be a bit clearer if it did.
Q3 look at http://gps.ordnancesurvey.co.uk/guide1.asp it surprised me
    also the image at
http://www.colorado.edu/geography/gcraft/notes/datum/gif/shift.gif
   show how the "datum" aka non spherical earths can affect positioning.
Q4 The distance is indeed distorted... because the earth isn't
spherical the on the ground distance isn't the same (even if the world
was all water with no moon)

On the other hand there are so many possibilities I think we should
pick one, pragmatically WGS84 seems to be a de-facto standard.

Andrew Rowbottom