Pointless

The pointless program (see Scaling and Assessment of Data Quality, Philip Evans, Acta Cryst D 62, 72-82) serves to identify space group possibilities from unmerged data.

The newest version may be obtained from ftp://ftp.mrc-lmb.cam.ac.uk/pub/pre/ . HTML documentation is at http://www.ccp4.ac.uk/html/pointless.html

Typical usage for space group determination is

pointless xdsin XDS_ASCII.HKL

Typical usage for converting to multi-record MTZ file (for scaling with SCALA) is

pointless -copy xdsin XDS_ASCII.HKL hklout XDS_ASCII.mtz

(the -copy option does not seem to be required for the latest versions)

More complicated operations may be scripted:

#!/bin/csh -f
pointless <<eof
xdsin XDS_ASCII.HKL
centre
eof

will make an R-factor search for the correct origin.

Attention: the space group number that pointless writes into the logfile (e.g. "18") is the generic one (as in the International Tables vol A), not the specific one (which could be 18, 2018 or 3018) that is used as a special convention within CCP4 to encode which of a,b and c is the two-fold axis. At the same time, pointless re-indexes orthorhombic such that a<b<c : this is what is called "cell-based setting" in the pointless documentation. However, users of XDSCONV want the "symmetry-based setting" because XDSCONV does not understand 2018 and 3018 (and those numbers are not even in the logfile, only in the MTZ file which is not used by XDSCONV anyway).

The upshot is: for space groups 17 and 18, one wants to use the "symmetry-based setting". It does not hurt to always (i.e. for all 65 space groups that proteins crystallize in) use it, so an easy way is e.g.:

echo -e SETTING SYMMETRY-BASED\\n CHIRALITY CHIRAL | pointless xdsin XDS_ASCII.HKL

which also shows how to send several commands to pointless.