[Proj] Geo Transfoms and calculations

Till till at free.fr
Mon Dec 29 19:07:28 EST 2008

Hi all,

We're quite new to geographic fundamentals, but it sounds like PROJ.4 is a
pretty good base where to find proper 'geographic related' libraries.

We're currently working on graphic (2D/3D) tools for displaying accurate GPS
information and our goal is to rely on standard systems, avoiding to
'reinvent the wheel', feeling it should be much of a benefit if we could
share with the community.

By now, we were able to properly use the 'proj' API in order to match
different projection schemes into 'Cartesian' (3D space) coordinates, and
also mix 2D representations.

However, distance calculation seems to be another issue.

While we could find ways to implement a reasonable calculation

(for instance :

gpsDist(PointF P1, PointF P2)


return Acos( sin(P1.y)*sin(P2.y) + cos(P1.y)*cos(P2.y)*cos(P1.x-P2.x) ) *


our approach considers it could be concentrated on the same system, in order
to provide consistency (at least sharing 'earthRadius' values).

In that manner, we failed to use 'geod' or affiliate as API.

We have to say that we're developing on Windows platform (VS 2005), and
we're lacking sample/tutorial/help for such a use.

Any help in that manner would be welcome.


PS: Is there a proper (recommended) way to increase 'ellipsoid' definitions
(increasing or modifying  'pj_ellps' table, for instance changing "sphere"'s

-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.maptools.org/pipermail/proj/attachments/20081230/5f9db04f/attachment.htm 

More information about the Proj mailing list