# [Chimera-users] plane normal axis

Elaine Meng meng at cgl.ucsf.edu
Tue Apr 7 11:51:37 PDT 2015

```My way would definitely require python, to calculate coordinates for the second atom and to create the atoms (there's no Chimera command for that).

Your way might be possible to make into an alias, since you can use the "define" command.

Elaine

On Apr 7, 2015, at 11:32 AM, Oliver Clarke <olibclarke at gmail.com> wrote:

> Thanks Elaine, that’s very helpful indeed. The other way I figured out was to define two centroids using a single atom from each subunit in the channel from two sets of residues in different planes (which would otherwise define two parallel planes) and define an axis from the two resultant centroids. Your way looks more general though - I will see if I can figure out a way to put it into an alias so I can call it with a single command.
>
> Best,
> Oliver.
>
>
>> On Apr 7, 2015, at 1:09 PM, Elaine Meng <meng at cgl.ucsf.edu> wrote:
>>
>> Hi Oliver,
>> If you have a plane defined in Axes/Planes/Centroids, you can write out its information including the normal (Save button on that tool), then place atoms at either end allowing you to define the axis.  There are a few steps...
>>
>> In my little test, the plane output information included:
>>
>> Planes
>> plane name, ID, center, normal, radius
>> plane: p1 ( 19.023,  17.733,   7.080) (-0.380,  0.757,  0.531) 24.199
>>
>> Then I used Tools… Build Structure, Start Structure, add atom at specific coordinates to add two atoms, one at the center of that plane and one to show the normal.  The  latter's coordinates are (center + normal) coordinates, and you can multiply the normal coordinates by some constant to make the axis longer.  For example, I multiplied the normal coordinates by 10 before adding them to the center coordinates to give the position of the second atom as:
>>
>> x 15.223   y 25.303   z 12.390
>>
>> Then I selected the two new atoms and used them to define an axis in Axes/Planes/Centroids, see attached image.
>> I hope this helps,
>> Elaine
>> ----------
>> Elaine C. Meng, Ph.D.
>> UCSF Computer Graphics Lab (Chimera team) and Babbitt Lab
>> Department of Pharmaceutical Chemistry
>> University of California, San Francisco
>>
>> <junk.png>
>>
>> On Apr 6, 2015, at 5:01 PM, Oliver Clarke <olibclarke at gmail.com> wrote:
>>
>>> Alternatively, would it be possible (or is there some way already) to define a separate axis that is the normal of a plane? In this case I’m working with an ion channel, so I’m looking for a consistent way to represent the change in orientation of particular extramembrane domains with respect to the channel axis. If I could define an axis for the membrane plane normal, I could at least measure the absolute orientation of the principal axes of particular domains or individual helices with respect to the channel axis. It seems like the plane normal is computed already (because there is an option in axes/planes/centroids) to align screen x/y/z to it, but I can’t see a way to generate it as a separate axis that I can use for measuring angles etc.
>>>
>>> Thanks for all your help as always!
>>>
>>> Oliver.
>>
>>
>

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