# [Proj] Zero level to air navigation

Clifford J Mugnier cjmce at lsu.edu
Wed Dec 3 13:27:58 EST 2008

```Janne,

They are not introducing new ellipsoids all the time.  The last one was 1980 with a trivial modification due to a different gravity term in 1984.

It was "all the time" in the 19th and 20th centuries.  They have figured it out by now ...

C. Mugnier
LSU

________________________________

From: proj-bounces at lists.maptools.org on behalf of support.mn at elisanet.fi
Sent: Wed 03-Dec-08 10:17
To: proj at lists.maptools.org
Subject: [Proj] Zero level to air navigation

Hello,

if sombody asked me so I would maybe set some simple sphere as the zero reference for the earth. Why? Because it is the most simple solution and you only need to remember it's radius. Now we have several ellipsoids and do they help anything... mostly not, since the earth is not even an ellipsoid. Earth has mountains and walleys, the real surface is complex, even the mean sea level is not any ellipsoid. So even the best ellipsoid is just an imagenary surface somewhere (nobody cares?).. except when they crash with the mountain.

To lessen the system complexity it would maybe be much more simple to take some well defined mean sphere surface as the reference! It would give larger distances to the actual surface, but who cares. It would just be a zero reference. All actual earth surfaces would have soething +/- to that. No we have thousends of ellipsoids and nobody knows exactly where the reference is and the possibility to make errors is much larger.

For example air navigation would benefit lot, since the absolute level is very important and the reference must be stable.

Maybe the WGS84 reference ellipsoid will be that  zero? The only problem with ellipsoids is that they are all the time introdusing new ones. If it was a sphere, then they probably would only change it's radius all the time? :)

Janne.

_______________________________________________
Proj mailing list
Proj at lists.maptools.org
http://lists.maptools.org/mailman/listinfo/proj

-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.maptools.org/pipermail/proj/attachments/20081203/b95183c5/attachment.html
```