[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: Masking

***  For details on how to be removed from this list visit the  ***
***    CCP4 home page http://www.dl.ac.uk/CCP/CCP4/main.html    ***

On Wed, 27 Oct 1999, Fred. Vellieux wrote:
> David J. Schuller wrote:
> > there is no such thing as maskless averaging.
> I do not agree with this statement. A properly conceived density averaging
> program will offer this possibility.
[followed by a lengthy discussion of auto-masking and proper vs. improper

allow me to repeat my statement, in context:
> there is no such thing as maskless averaging. averaging always uses a
> mask, whether you specify it yourself or let some program calculate it
> for you.

i believe what you describe is the generation of an averaging mask within
the averaging program.  to me, that would be a perfect example of "letting
some program calculate a mask for you".  it is only by masking out the
context that you were able to isolate something with which you could

as for the separate question of whether a "properly conceived density
averaging program" will do auto-masking, i happen to disagree with you.
this is a result of my experience both with structures having
improper NCS and with structures requiring multi-domain averaging,
another situation for which auto-masking is inappropriate.
auto-masking may be a convenience for simple cases of NCS, but its absence
would in no way make an averaging program "improper" or incorrect.


     Crystals are pretty, but they just kind of sit there,
         not doing much of anything.  - Larry Wall
                        David J. Schuller
                        modern man in a post-modern world
                        University of California-Irvine