Objects are 'shaking' in space using big coordinates.

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1

Hello,

I have a problem in Panda3D application where I try to simulate gravity - a body going around another body.

“1.0” for me is considered one meter, and so body (a sphere) has a radius of “10.0” and is going around object (earth) with radius of “6371000.0”, having a mass of

EARTH_MASS = 5.98 * 1000000.0 * 1000000.0 * 1000000.0 * 1000000.0

So it’s big numbers, and the problem is that in the end of all calculations I get few HEAVILY SHAKING objects: space body, two (velocity and gravity visualizers) vectors are shaking, and looks like camera (which is a child of space body) itself shakes also! And they all do that rather asynchronously.

Well, I have some calculation uncertainty - for example, altitude (you can see that printed in console) is moving up and down for a “0.5” units, but as for that “shanking” I guess it’s not the case, since two vector nodepaths has the same “setPos()” as body, and camera is reparented to the body itself. So I could expect to see all of them in exact same place, right?

Please take a look:
vacuum_2010-11-07.zip

I’ve placed “time.sleep()” in every frame to slow down and see it more clearly.

Thank you.

P.S. I’m using Panda3D 1.6.2 in Ubuntu 10.10 32bit.

2

Graphics cards are not designed to handle the scales found in space which may be the issue you are having at the moment. What I did is separated the simulation and graphics. Simulation is 1 panda unit = 1 meter, but the graphics layer scales the object down instead when it gets over 10,000 units away. The camera can rotate but I move the planets instead of moving the camera. My code is a bit messy but I am more than happy to post it.

3

Thast’s great idea, croxis, but can “Point3(17725.2, 0, 6.73098e+06)” be already too big? :open_mouth: I mean, magnitude does not reach a million.

4

talkless. keep in mind we’r also dealing with rotations here. and, when rotations are messing aroudn you always have to translate coordinates with sin and cos on a low level (panda hides that from you). if you change an angle by a tiny little bit. a point rotated in 100thousand units distance would suffer from quite some noticeable error due to rounding.

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6.73098e+06 is not too big for computation, but that scale gets too big for graphics cards

6

Or this “shaking” is due to the fact that your float is getting “imprecise” for big number. Reason: en.wikipedia.org/wiki/Single_pre … int_format -> for big numbers the “lower” parts are cut of