Celestia Forums

Hello,


In english wikipedia page about Celestia, you can read that Celestia's Earth shape is not realistic : it's a sphere whereas it would be an ellipse or that Celestia's model for Earth has not its poles flattened. Is it still exact?

Thanks in advance.

Imy,

The Wikipedia entry needs to be reworded.

Here's a lengthier description of the problem.

The Earth is not a sphere, which is Celestia's default representation.
The Earth is not an oblate spheroid, which Celestia also can represent (it happens to be commented out right now), and to which you seem to be referring.
Some people describe the Earth as "pear shaped" which is closer, but even that isn't right.

At the precision required to be able to accurately display the direction from a viewpoint on the ground toward a satellite in low orbit, the Earth is extremely irregular. I am not referring only to the obvious height differences caused by mountainous terrain (which Celestia does not model.) Even the maps of every country have to be drawn with respect to "the local geoid" -- the shape of the Earth in their vicinity. Large countries (like the U.S.) use several different geoids for their maps.

Learning more about this topic is left as an exercise for the student.

What about modelising Earth not like a geometric object but like asteroids are today in Celestia (for instance Toutatis which uses a 3D model)? Using altimetric data, it could be a way to have the difficulte shape of Earth and it'd be a first step for Celestia to represente the surface relief? We can do so that only for our own planet (with which we have a lot information), can't we?

It could be interesting using such Earth's shape for having shots of the famous earth horizon from spatial orbit.

A add-on may exist?

That sounds like a reasonable project for some enterprising individual!

Why don't you give it a try?

Imy wrote:What about modelising Earth not like a geometric object but like asteroids are today in Celestia (for instance Toutatis which uses a 3D model)? Using altimetric data,............
A add-on may exist?

Possibly, I'm not sure how the model was built but.........
http://www.celestiamotherlode.net/catal ... system.php
Eath Model 1x cmod by Globe Maker
cartrite

Well, I think I'm not the best one to do such job... I don't know a lot in 3D modelising and specially for Celestia models. More, today I don't know where to find free data, anyone has an idea?

I doubt about this kind of modelising could be done on our computers today : we need a lot of polygons to draw the quasi elliptic shape of the Earth that's to say the cpu would go up quickly. So quickly that any other object would be able to be added like orbital objects. More, i'm not sure that 3D cards can draw it enough quickly for a fluently 3D movement, can't they?

thanks cartrite. I'm going to try that (i need some times to download such big files for me )

I might misuse these addons (i tried The Earth 1x and 2x). I don't feel exciting viewing 1x : either there is no altitudes or new Celestia can't now show them correctly...
What is more interesting: general 3D surface relief as i've suggested,a cluster of 3d local models like a famous Mars or Titan probe landing add-on, or specular light surface image?