double precision function kutl_2vertex_err(z1, Vz1, z2, Vz2)
*
* begin_doc
*
*  Returns the error along line connecting two vertices.
*
*  Input Parameters:
*  z1(3)          double precision array
*                 Vertex 1
*
*  Vz1(3,3)       double precision array
*                 3x3 covariance matrix for z1
*
*  z2(3)          double precision array
*                 Vertex 2
*
*  Vz2(3,3)       double precision array
*                 3x3 covariance matrix for z2
*
*  Output Parameters:
*
*  Return value:
*                Sigma of the distance between the two vertices along
*                line connecting them.
*
*  Other routines:
*
*  Notes:
*
*  Author:   Paul Avery      Created:  Tue Sep 23 23:10:11 EDT 1997
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*  Major revisions:
*
*
* end_doc