[chimerax-users] Alternate locations

[Eric Pettersen]

Hi Gunnar,
	Glad you like the program!  Our experience with the design of Chimera and Midas before it allowed us to identify what we felt was good and what we felt could be improved, and ChimeraX has benefited from that in many ways.
	The handling of alternate locations was one of the things that changed between Chimera and ChimeraX.  In Chimera, each alternate location was treated as a completely separate atom, and therefore they were all displayed at once, but the flip side of that is that it made some kinds of chemical computations much uglier in that it was much more work to figure out how many bonds a specific atom had if its neighbor atoms had alternate locations.  In ChimeraX, there is only one atom, which can have several alternate locations.  You switch between them by setting the atom's alternate location identifier, which will not only switch that atom's location, but all related nearby alternate locations so that the set of alternate locations are consistent.
	We haven't developed a user interface to alternate locations yet, so the only way to set the alternate location (outside of Python code) is with the "setattr" command.  So to set your example atom's alternate location to 'B' the command would be:

	setattr /A:8 at NE2 a alt_loc B

(FYI, assuming the structure has no lower-case chains, both the chain ID and atom name could be typed in lower case)

	You don't describe what you will be using the alternate locations for, but if you did that might help shape the design of the user interface that we eventually develop for alternate locations.

--Eric

	Eric Pettersen
	UCSF Computer Graphics Lab


> On Jul 23, 2020, at 11:07 PM, Jeschke Gunnar <gunnar.jeschke at phys.chem.ethz.ch> wrote:
> 
> Hi ChimeraX team,
> 
> very nice program and remote control scheme! Clear thinking, cool implementation.
> 
> My question/suggestion is about alternate atom locations. ChimeraX knows about them. 
> 
> I load 1lcd
> 
> info atoms /A:8 at NE2 attribute alt_locs
> 
> correctly responds:
> 
> atom id /A:8 at NE2 alt_locs A,B
> 
> When I show /A:8 at NE2 or I show /A:8 as sticks, only location A is displayed. When I retrieve atom coordinates, only location A is returned.
> 
> Could you implement full handling of alternate locations (or am I doing something wrong here? I really tried a lot to find location B).
> 
> Kind regards
> 
> Gunnar
> 
> ---
> 
> Der Schlaf der Vernunft gebiert Ungeheuer - Francisco Goya
> 
> Prof. Dr. Gunnar Jeschke
> ETH Zurich
> Department of Chemistry and Applied Biosciences
> Vladimir-Prelog-Weg 2
> CH-8093 Zurich Switzerland
> 
> www.epr.ethz.ch
> 
> _______________________________________________
> ChimeraX-users mailing list
> ChimeraX-users at cgl.ucsf.edu
> Manage subscription:
> https://www.rbvi.ucsf.edu/mailman/listinfo/chimerax-users