Crystallography Online: the website of the International Union of Crystallography

The next imgCIF dictionary proposal will include maps.  Joe has been
looking at an early version of it.

The SBEVSL project will be proposing very general operator handling
for symmetry, NCS and for the transforms needed for work in
graphics.

I'll be bringing along material on these to the ACA meeting and
to BSR 2007.

   -- Herbert



At 2:08 PM -0400 3/22/07, David Brown wrote:
>Joe Krahn wrote:
>
>>How many people are working on the new electron-density dictionary?
>>
>The electron density dictionary is part of the corpus of approved 
>CIF dictionaries, but it is designed to report accurate electron 
>density measurement on small cell crystals using atom-centered 
>multipole functions.  I suspect you are looking for lower resolution 
>elelctron density maps of protein molecules and I am not aware of 
>any group working on a CIF representation of that.
>
>>
>>So, matrix/vector symmetry should be supported. Are there opinions as to
>>whether the equation method should or should not also be supported for
>>things like electron-density maps?
>>
>Dictionaries defined using DDLm (previously DDL3) allow matrices and 
>vectors to be reported as a single item.  It is the awkwardness of 
>the presentation of matrices in DDL1 and DDL2 dictionaries that 
>discouraged us from defining a matrix+vector representation of 
>symmetry operations in the current suite of dictionaries.  CIF also 
>supports the use of the Hall space group symbol which uniquely 
>defines the space group operations, hence the space group and its 
>setting.  It is thus more informative than the Hermann-Mauguin 
>symbol which does not uniquely specify the origin.
>
>David Brown
>Chair COMCIFS
>
>
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