Re: [Imgcif-l] ImgCIF Densiry Maps

[David Brown <idbrown@mcmaster.ca>]

Joe Krahn wrote:

>What about equation forms? It is important to define more than just the
>space group, because non-standard settings can be useful in some cases.
>
The Hall symbol is a space group name (symbol) that specifies all 
possible settings of the 230 regular space groups.  It can easily be 
expanded into the list of the expressions of symmetry operations.

>It is also useful to include matrix+vector for such things as a
>spherical asymmetric unit from a 72-fold symmetric virus map. If nobody
>is working on it, maybe I should go ahead and write down a few
>alternatives and check opinions of other macro-molecular crystallographers.
>
This would be useful.  I assume that the existing format could be 
extended using notation such as x/72,y-56/72 etc.  CIF does have 
definitions for symmetry operations in higher dimensions, but not, I 
believe, for non-crystallographic symmetries

David Brown


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