[ccp4bb] XDS and overlaps

[Engin Ozkan]

Hi everyone,

I have been recently relying on XDS quite a bit, but at the same time 
worrying about how XDS treats overlaps.  We had one dataset that both 
HKL2000 and Mosflm would show to have severe overlaps, as expected due 
to unit cell parameters and the unfortunate crystal orientation in the 
loop. We always ended up with completeness percentages in the 70's.

XDS can find the same lattice, index and scale the data, but yields a 
100% complete mtz (and a nice structure). Without the HKL/Mosflm-like 
GUI, it is difficult to assess the fate of the overlapped observations 
in XDS. What I could see with VIEW was that some observations were being 
divided into several ovals, probably different reflections, but I'm not 
very certain.

So, the basic question is, how does XDS treat overlaps?  I could not 
find in the documentation an answer to this question; the single mention 
of overlaps I could find tells me that XDS can recognize overlaps, but 
does not tell me if it rejects them, or divvies them up into separate 
reflections, and if that is the case, how does it divide them, and how 
reliable is that? Depending on how it divides the overlaps, could that 
affect commonly-used intensity stats and distributions?

Thanks,

Engin