Merely encoding our state of knowledge of the space group into the file header doesn't introduce any additional constraint. The very fact that we are uncertain of the correct space group, whether or not that information is encoded, is already a constraint on what operations can be sensibly performed on the data.
The unit cell and indexing is uniquely determined by the Bravais lattice assigned at auto-indexing time, except in the case where you have already indexed another isomorphous (or near-isomorphous) dataset, and the default indexing may not be what you want, so provided the Bravais lattice has been chosen correctly then no re-indexing will be needed when the space group is assigned. Provided you stick to the conventional cell choice based on the Bravais lattice type, then the selection of space group for a given Bravais lattice has no bearing whatsoever on the indexing. Of course if you made the incorrect choice of Bravais lattice originally, you're going to have to start over anyway. -- Ian > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Kevin Cowtan > Sent: 09 November 2007 14:52 > To: [EMAIL PROTECTED] > Cc: [email protected] > Subject: Re: [ccp4bb] pointless (1.2.0) and enantiomorphic SG's > > Eleanor Dodson wrote: > > Offering a selection of space groups compatible with a > point group will > > not require reindexing. > > Some point groups of course permit reindexing, but one hope > you have > > chosen a consistent set as you combine data sets into an MTZ file - > > pointless and the GUI both offer ways to check this. > > > > Phasing cannot be carried out till you have chosen a > spacegroup, and any > > existing phase associated data should probably be weeded > out as part of > > a "Assign Spacegroup" function. > > Good, that makes sense. > > Note however we have introduced a constraint on the data model: > - Phasing and multiple spacegroups are inconsistent. > > Actually, IIUC, it's more complicated, since heavy atom > location comes > before phasing, but produces phases with enantiomorph ambiguity. > Grahame's 4-step indicator of uncertainty provides the right sort of > framework. But each step is associated with a corresponding set of > restrictions on what is valid in the file - and in the case > of phases, > what they actually mean. > > Disclaimer This communication is confidential and may contain privileged information intended solely for the named addressee(s). It may not be used or disclosed except for the purpose for which it has been sent. If you are not the intended recipient you must not review, use, disclose, copy, distribute or take any action in reliance upon it. If you have received this communication in error, please notify Astex Therapeutics Ltd by emailing [EMAIL PROTECTED] and destroy all copies of the message and any attached documents. Astex Therapeutics Ltd monitors, controls and protects all its messaging traffic in compliance with its corporate email policy. The Company accepts no liability or responsibility for any onward transmission or use of emails and attachments having left the Astex Therapeutics domain. Unless expressly stated, opinions in this message are those of the individual sender and not of Astex Therapeutics Ltd. The recipient should check this email and any attachments for the presence of computer viruses. Astex Therapeutics Ltd accepts no liability for damage caused by any virus transmitted by this email. E-mail is susceptible to data corruption, interception, unauthorized amendment, and tampering, Astex Therapeutics Ltd only send and receive e-mails on the basis that the Company is not liable for any such alteration or any consequences thereof. Astex Therapeutics Ltd., Registered in England at 436 Cambridge Science Park, Cambridge CB4 0QA under number 3751674
