I'm trying to compute Mean Anomoly. Mean Anomoly is an angle that describes where in an orbit an object is relative to its periapsis. The formula according to Wikipedia is(adsbygoogle = window.adsbygoogle || []).push({});

[tex]

M = E - e \cdot \sin E

[/tex]

where e is eccentricity (which I know), and E is Eccentric Anomoly.

According to Wikipedia, Eccentric Anomoly is

[tex]

E = \arccos \frac{{1 - \left| r \right|/a}}{e}

[/tex]

where a is Semi-Major Axis (which I know), e is eccentricity (which I know), and r is an orbiting body's position vector. If I solve for r, I'm home free.

According to Wikipedia, The orbital position vector r is a cartesian vector describing the position of the orbiting body. Wouldn't that mean that r would be express as something like 1.0i + 2.0j+3.0k? But I can't plug something like that into the formula for Eccentric Anomoly. I could use Pothagorean Theorum to solve for distance and use this number. But that turns the vector into a scalar, and I doubt that's the right way to do it. Direction is pretty important here.

I know the object's x, y, and z position wrt the reference frame. How do I turn r into something I can use in these formulas?

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# Vector confusion

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