xyzv trajectory file's velocity

[Joe]

Hi, Celestia users

Anyone would shed some light on the effect of the velocity elements in a xyzv trajectory file. The records in an xyzv file have three velocity values appended after each position, what are they for in Celestia 1.6.0? Do they have any effect on the orientation of the spacecraft in orbit at each position. Certainly its existence in a xyzv file does not have anything to do with how fast the spacecraft orbiting in space. What is the velocity for in Celestia 1.6.0 anyhow?

[duds26]

One reason they are useful is for interpolation.
In Celestia you can slow the time and accelerate it.
With a bunch of dots, celestia doesn't know where it has to draw the spaceship between those dots.
There are some nice interpolation algorithms, however it's induces errors.
Adding velocities makes interpolation much easier and more accurate for Celestia.

Hope this was a good answer to your question.
It could be that there are other advantages.

[Joe]

That helps a lot, duds26. Thanks .

I am having difficulties in figuring out the true effects of velocity (also angular velocity) coded in Celestia 1.6.0. I am not sure whether or not it controls the orientation of a spacecraft while the spaceship is in the trajectory. For instance, if the spaceship is flying in space along a xyzv trajectory, how we control its antenna to face the earth? Or how can we keep the spaceship's one axis (maybe Z-axis) always in tangent to the trajectory? Does the xyzv data help in achieving this or should I set it somehow in SCC file?

[selden]

xyzv files only provide position information. They have no affect on orientation. "SampledOrientation" files of quaternions can be used to provide comparable orientation information. However, one also can use a BodyFrame specification to cause one object to always face some other object.

See http://en.wikibooks.org/wiki/Celestia/R ... Sun_Locked

[Joe]

Thanks, Selden. A big helper as always you are.

[selden]

You're very welcome.

[Joe]

Hi

Anyone has experience in using "SampledOrientation" files to control the orientation of an object in orbit? There are a lot of examples/cases for using "SampledTrajectory" files (.xyz or xyzv) but I have come cross little reference in this forum about using SampledOrientation.

I am trying to fix a spaceship's orientation always in alignment with the direction of its velocity (or the tangency of its trajectory), anyone would help with the knowhow or point me to the right direction?

[selden]

To use a SampledOrientation file, you have to understand quaternions. Sorry: I can't help there.

However, you don't have to use a quaternion file in order to keep an object's orientation fixed relative to its motion. You can specify an TwoVector RelativeVelocity reference Frame which orients its axes dynamically.

See http://en.wikibooks.org/wiki/Celestia/R ... r_property