Finding the relative coordinates of the NoteHead/NoteColumn grob to which a glissando is going

[Mike Solomon]

Hey lilypond users,
    I am using my own stencil for a glissando object and would like to feed
it the exact X and Y extent it must traverse from its parent note grob to
the grob at which it ends.  ly:grob-property grob X-extent and
ly:grob-object grob X-extent give me the Boolean #f on both accounts, so
it's tough for me to grab the distance between two noteheads without
resorting to a kludge - right now, I am attaching a markup to the NoteHead
to which the glissando is going as a text identifier of sorts, searching for
this markup in the VerticalAxisGroup, and grabbing the relative position of
the NoteColumn to which said markup is attached.  There must be a better way
to go about this, and I am relative new to lilypond so I have yet to find it
- any help would be much appreciated!

Thanks thanks,
~Mike