# Calculate Euler Angles between two points?

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Does anybody know how I would calculate the Euler Angles between two geocentric points in space? Thanks!!!

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Ahhhhhhh there's no such thing as an angle between two points! [grin]

But there is such a thing as the angle between two vectors. I'm assuming you want the angle between the vectors that that points make with the origin, so in that case what you want to do is use the identity:

A.x*B.x + A.y*B.y + A.z*B.z = |A||B|cos(Θ)

And then just solve for Θ. Just eliminate A.z*B.z in two dimensions. The angle will only in the range [0, PI], so what you'll have to do is also take the cross-product between the two vectors to determine the ordering. In 2D, the Z component on your cross-product vector will be positive if the first vector comes before the second vector, sweeping CCW from a lesser angle to a greater angle, and negative otherwise.

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just out of interest, would someone tell me what geocentric points are? (doesn't happen to be related to planets???)

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Description of Geocentric Coordinates:
Geocentric coordinates are Cartesian coordinates (X, Y, Z) that define the position of a point with respect to the center of mass of the earth. The origin of the coordinate system is at the center of the reference ellipsoid.
The coordinate system is a right-handed system, with the positive X axis emerging from the ellipsoid at the equator on the prime meridian, and the positive Z axis emerging from the ellipsoid at the north pole.

thanks.

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yeh sounds like u want the angle between the vectors...

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