Eye Line 1.0
------------

REQUIREMENTS: VMD Version 1.1 or greater, use in orthographic mode

DESCRIPTION:
	After an atom has been picked, call "eye_line".  It generates a
	cylinder along the line joining the picked atom and the present
	eye position, assuming VMD is using an orthographic projection.  It 
	also prints the endpoints of the cylinder. eye_line takes no
	arguments.  In the past this procedure has been useful for steering
	portions of proteins through surface holes.

HOW IT WORKS:
        This example of a trace on the picked atom draws a line from the
        picked atom to the user's eye.  It is a good example of how to use
        matrices in \VMD.  The limitation to the following procedure is that
        it doesn't understand perspective viewing, so to make it work, use the
        orthographic mode.

        This was used to find the direction to pull a ligand from its bound
        position out of the protein.  The molecule was rotated until the user
        could look straight down to the ligand.  The user then picked an atom
        on the ligand, causing a line (actually, a cylinder)
        to be drawn from the atom past the eye location,
        and the start and end points of the cylinder were printed for
        later use.


PROCEDURES:
	eye_line - be sure to pick an atom before calling this

EXAMPLE OUTPUT
	Sample of eye_line being used to guide the retinal
	center of bacteriorhodopsin out through the membrane helices. This
	image has been rotated by 90 degrees to make the outward cylinder
	visible.



DOWNLOAD THE FILE:
	eye_line.tcl


AUTHOR:
	Andrew Dalke (dalke@ks.uiuc.edu)