Hi Andy, You could define a 3D arrow in the BILD format (a simple text format). Reading in the file will create the object in the Chimera scene. I guess the trickiest part is using geometry to figure out the xyz coordinates of the end that extends past the second atom or centroid. See the BILD format description and linked example files: <http://www.rbvi.ucsf.edu/chimera/docs/UsersGuide/bild.html> ChimeraX and Chimera both read this format. I hope this helps, Elaine ----- Elaine C. Meng, Ph.D. UCSF Chimera(X) team Department of Pharmaceutical Chemistry University of California, San Francisco

On Nov 20, 2019, at 2:58 PM, Byrd, Robert A. (NIH/NCI) [E] <byrdra@mail.nih.gov> wrote:

I would like to draw a vector that would extend the connection of two points in a model. This would allow better visualization. The current status is a line that joins between the centroid of a plane of atoms to another atom that is above the plane. I would like to extend this vector out into space for say 5 or 10 angstroms. This would allow visualization of the direction relative to the remainder of the molecule. All that I have been able to do is draw a line between the centroid and the atom. This does not give the perspective to other parts of the overall scene. In the attached image this would be the red bar connecting the centroid of the purple plane to the green atom. How would one extend this out 5-10 Angstroms? Ideas? Thanks Andy Byrd <cage-vector-draw.png>