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   Convert from the ECI frame to the NEH frame. This is the
   frame with x pointing north, y pointing east and U up from
   the earth's surface. This is not a right handed frame.
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   Form:
   rNEH  = RNEH( r, units )
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   ------
   Inputs
   ------
   r           (3,1) Position vector (m)
   units       (1,:) Units

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   Outputs
   -------
   rNEH        (3,1) [N;E;H]

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