Thanks Tom, that's great. 

We are also talking about adding an option to the measure rotation command to produce an Axis model but haven't settled on that yet (mostly because we think no one will know when to use it).

I can see why you'd be ambivalent about this. The fact that it's easy to define an axis from the pair of atoms that is currently output means there's a really quick workaround anyway.

Cheers,
Alexis

On Fri, Nov 17, 2023 at 11:35 AM Tom Goddard <goddard@sonic.net> wrote:
Hi Alexis,

  I made the "angle" command handle the measure rotation axes, so if you have two axes #3 and #4 you can just use

        angle #3,4

As Elaine mentioned each axis is just a pair of atoms and now the angle command can take 4 atoms defining two vectors.  We are also talking about adding an option to the measure rotation command to produce an Axis model but haven't settled on that yet (mostly because we think no one will know when to use it).

        Tom


> On Nov 16, 2023, at 5:35 PM, Tom Goddard via ChimeraX-users <chimerax-users@cgl.ucsf.edu> wrote:
>
> Hi Alexis,
>
>  Unfortunately the measure rotation code was written long before define axes and was never updated to make them compatible.  Since measure rotation has been around forever we probably are not going to change the model it makes since that will break the way people have been using it.  But we ought to add an option to allow creating an axis model.
>
>       Tom
>
>
>> On Nov 16, 2023, at 5:26 PM, Elaine Meng via ChimeraX-users <chimerax-users@cgl.ucsf.edu> wrote:
>>
>> Hello Alexis,
>> The axis representations from "measure rotation" are actually marker models, just two markers (dummy atoms) with a link (bond) between them, and not axis objects proper.  I agree it is very confusing because they represent axes and look almost the same as the axis objects, which are cylindrical.
>>
>> <https://rbvi.ucsf.edu/chimerax/docs/user/commands/measure.html#rotation>
>>
>> As I understand it, only the "define" command and the Axes/Planes/Centroids tool create axis objects proper.
>>
>> That's not to disregard your suggestion, which makes sense.
>>
>> However, the current workaround is to select the two markers at the ends of the "measure rotation" marker model and use "define" or the Axes/Planes/Centroids tool to create an axis object from them.
>>
>> Best,
>> Elaine
>> -----
>> Elaine C. Meng, Ph.D.                       
>> UCSF Chimera(X) team
>> Department of Pharmaceutical Chemistry
>> University of California, San Francisco
>>
>>> On Nov 16, 2023, at 5:19 PM, Alexis Rohou via ChimeraX-users <chimerax-users@cgl.ucsf.edu> wrote:
>>>
>>> Hello again,
>>>
>>> I have been using "measure rotation" to create several rotation axis objects, with the goal to measure angles between the various axes.
>>>
>>> Two of my axes are #4 and #5.
>>>
>>> When I try to measure the angle with "angle #4 #5", I get the error:
>>> "Must specify exactly 3 atoms/centroids or two measurable objects (e.g. axes/planes)"
>>>
>>> I notice also that the axes created by "measure rotation" do not show up in the "Structure Measurement" UI tool, which I guess is related.
>>>
>>> Would it be possible to please amend the output of the "measure rotation" command so that the axis (and slabs) it outputs are measurable?
>>>
>>> Cheers,
>>> Alexis
>>
>>
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