[cctbxbb] Asymmetric Unit with cctbx

[Ralf W. Grosse-Kunstleve]

Hi Phillip,

Could you give a brief overview of what you want to do?
There are many ways of handling the contiguous asu information, but
how much effort a particular approach is worth highly depends on
the application. E.g. it is important to understand how important
runtime performance is vs. memory use vs. developer time.
Note that the contiguous asymmetric units are fully defined in the
cctbx.sgtbx.direct_space_asu module (this is behind the asu gallery
Peter pointed out). However, the full information for handling all
conditions on the facets, edges and vertices is only available in
Python. For processing maps this is likely to be too slow, unless you
really don't care about runtime.
In C++, the contiguous asymmetric units are only used as
volumes: cctbx/crystal/direct_space_asu.h, classes float_cut_plane
and float_asu, which duplicate some of the Python code. It is not
a severe duplication since the facet/edge/vertex conditions are
meaningless when working with floating-point numbers and can therefore
be dropped. When dealing with grid points in maps you need those
conditions somehow, either from some sort of reference table as
we have in Python, or by looping over the symmetry operations.
Handling the full conditions in C++ would be quite a bit of work,
I think. It would be cool to have in general, but so far I didn't
have an application important enough to justify the effort.

Ralf




 
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