Dear All;
With regards both to my original question and the recent question by
Katja Schleider, I have been told by Mike Sawaya that he has just
implemented an option for inputting the B-factor's of your choice to
his server (http://www.doe-mbi.ucla.edu/~sawaya/anisoscale/). This
option allows for an aniostropic resolution limit and no change to the
user's Fo's if desired.
Katja, my personal solution had been to impose an elliptical
resolution limit to minimize the amount of erroneous data (see below)
though that comes with some caveats as described below:
From my original summary:
Application of a elliptical resolution boundary is justified because
the resolution boundary from common integration programs (Denzo and
Mosflm for example) is spherical where diffraction for anisotropic
data is ellipsoidal. A spherical boundary would result in the
inclusion of numerous poorly measured reflections in the higher
resolution shells which effectively makes these data more noisy.
Imposing an ellipsoidal resolution boundary is equivalent to removing
noise from the higher resolution bins and is simply the anisotropic
equivalent of the normal resolution limit truncation.
from Peter Zwart
Hi Justin,
Please be careful in interpreting maps from elliptically truncated
maps, there is a potential for introducing some bias. In Refmac (as
well and Phenix) maps are produced that fill in missing amplitudes
with DFcalc. When your mtz file contains only a small fraction of
miller indices in the highest (spherical) shell, all the missing
reflections will be assigned DFcalc. Depending on your anisotropy,
this can be a significant number of reflections.
I'm not sure how serious this issue is, but it might be worthwhile
checking the 'unfilled' maps as well (both phenix.refine and Refmac
allow you to compute these).
HTH
Peter
I hope this helps, good luck Katja.
