Dear Tim, It could be that COLSPOT does not rely on experimental setup parameters. However, XDS must have reasonably close starting values for distance, direct beam position etc., otherwise the autoindexing would fail, so the information to calculate an approximate TRUSTED_REGION is available.
For good data, a limited spot range usually works as well. However, for the weakly diffracting bad crystals with ice rings, salt spots, multiple diffraction patterns etc., one often needs the full range and often needs several tries with different parameters before indexing is successful. Since it is only cpu-time, it is the least of my worries and, as you mention, it is not bad to be forced to think once in a while instead of just clicking buttons in GUI's. Best regards, Herman -----Original Message----- From: Tim Gruene [mailto:t...@shelx.uni-ac.gwdg.de] Sent: Wednesday, March 20, 2013 11:17 PM To: Schreuder, Herman R&D/DE Cc: CCP4BB@JISCMAIL.AC.UK Subject: Re: [ccp4bb] Resolution limit of index in XDS -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Dear Herman, the short answer might be that at the stage of COLSPOT the term 'resolution' has a limited meaning because COLSPOT does not rely on the experimental setup like distance and beam direction, so the term 'resolution limit' is conceptually not applicable at this stage. Indexing does often not require the full data set, you can reduce the "SPOT_RANGE" if you are worried about processing time, or by a multi-CPU machine. One of the great advantages of XDS is that it asks you to think at a level higher than the average MS-Windows user while processing your data, so the effort to figure out the three numbers to set the TRUSTED_REGION is in line with the philosphy of XDS as I understand it. But you are right, I do not have access to the source of XDS and I am not the person to address a request to. Kind regards, Tim On 03/20/2013 10:29 AM, herman.schreu...@sanofi.com wrote: > Dear Tim, but probably I should adres this to Kai Diederichs, > > not including the resolution cutoff in COLSPOT and IDXREF is a feature > of XDS I do not understand at all. For most cases, it may not matter > since only the strong spots are used, but what are the advantages? > > In fact there are disadvantages, especially when dealing with poorly > diffracting difficult data sets: -when a crystallographer imposes a > resolution limit, there are usually good reasons for it. > -outside the resolution limit, there may be ice rings or contaminating > salt spots, which make the autoindexing fail. -when processing 900 > frame Pilatus data sets, running COLSPOT on the complete detector > surface takes significantly longer then running it only on the center > region. > > Of course, one could fudge a resolution cutoff by translating > resolution into pixels and then calculating a TRUSTED_REGION, or > manually editing the SPOT.XDS file, but this is a lot of extra and in > my view unneccessary work. > > I would really consider using the resolution cutoff for COLSPOT as > well. > > Best, Herman > > > -----Original Message----- From: CCP4 bulletin board > [mailto:CCP4BB@JISCMAIL.AC.UK] On Behalf Of Tim Gruene Sent: > Tuesday, March 19, 2013 11:06 PM To: CCP4BB@JISCMAIL.AC.UK Subject: > Re: [ccp4bb] Resolution limit of index in XDS > > Dear Niu, > > indexing relies on strong reflections only, that is (in very > brieft) why INCLUDE_RESOLUTION_RANGE indeed does not affect the > relections collected in COLSPOT which in turn are used by IDXREF. > You can work around this, however, by making use of TRUSTED_REGION and > set it to e.g. 0.7 or 0.6 (you can use adxv to translate resolution > into pixel and then calculate the fraction you need to set the second > number in TRUSTED_REGION to (or the first if you want to exclude the > inner resolution reflections - I remember one data set where this was > essential for indexing - DNA was involved > there) > > Best, Tim > > On 03/19/2013 08:53 PM, Niu Tou wrote: >> Dear All, > >> Is there any command can set the resolution limit for index step in >> XDS? I only found a keyword INCLUDE_RESOLUTION_RANGE, but it looks to >> be a definition of resolution range after index step as it says: > >> INCLUDE_RESOLUTION_RANGE=20.0 0.0 !Angstroem; used by >> DEFPIX,INTEGRATE,CORRECT > >> Thanks! Niu > > > - -- Dr Tim Gruene Institut fuer anorganische Chemie Tammannstr. 4 D-37077 Goettingen GPG Key ID = A46BEE1A -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iD8DBQFRSjVtUxlJ7aRr7hoRApZhAJ9RFBs8D9NGjgLY3KOoNHhNtdOWggCgj7U0 zY7jEFDYZfl0Umb9E1Bzs1U= =+HjR -----END PGP SIGNATURE-----
