Of course, you may need to re-index even if you have the right space
group...
> 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.
>
>
> Eleanor
>
>
>
> Kevin Cowtan wrote:
>> This is great! But before we all get carried away, a quick reality
>> check is in order. This isn't an area I've thought about, but my
>> limited understanding raises the following issues....
>>
>> Given that an MTZ file contains a cell, an indexing of the data, and
>> possibly phases involving a choice of origin, the use of an MTZ file
>> immediately implies that some decision has been made about the
>> spacegroup.
>>
>> Selecting a different spacegroup from a list of possibilities may
>> involve reindexing, and/or changing origin/enantiomorph dependent
>> properties such as phases and HLs.
>>
>> It would be possible for an MTZ file to say something like this:
>> 'This file is generated assuming spacegroup X. Spacegroups X1, X2,
>> X3, X4, X5.... are also possible.'.
>>
>> It should also be possible to compute on the fly whether a particular
>> column type needs to be modified for a different spacegroup.
>>
>> How will we present this in user interfaces? As a starting point,
>> until a spacegroup has been settled upon, the user will need the
>> option of picking the spacegroup after having selected the MTZ. This
>> means potentially a reindexing step added to every single task -
>> messy. As an intermediate, being able to change the 'currently
>> selected' spacegroup as a separate task would be an improvement.
>>
>>
>> Phil Evans wrote:
>>> I agree
>>>
>>> On 9 Nov 2007, at 13:50, Eleanor Dodson wrote:
>>>
>>>> As I often say!!! The mtz format should carry point group and
>>>> alternate SGs - then be upgraded when youknow the correct SG..
>>>>
>>>> Eleanor
>>>>
>>>> Phil Evans wrote:
>>>>> It just picks the first in the list, to store in the output MTZ
>>>>> file, which can only handle one (92 < 96)
>>>>> Phil
>>>>>
>>>>>
>>>>> On 8 Nov 2007, at 22:26, Bryan W. Lepore wrote:
>>>>>
>>>>>> when pointless (1.2.0) finds enantiomorphic SG's, what is the
>>>>>> criterion for 'Selecting' one over the other?
>>>>>>
>>>>>> e.g. i ran pointless on some tetragonal data, and the
>>>>>> enantiomorphs SG92/SG96 are selected as strong candidates
>>>>>>
>>>>>> Spacegroup TotProb SysAbsProb Reindex
>>>>>> Conditions
>>>>>> <P 41 21 2> ( 92) 0.956 0.956 00l:
>>>>>> l=4n, h00: h=2n (zones 1,2)
>>>>>> <P 43 21 2> ( 96) 0.956 0.956 00l:
>>>>>> l=4n, h00: h=2n (zones 1,2)
>>>>>>
>>>>>> ... then pointless reports :
>>>>>>
>>>>>> Selecting space group P 41 21 2 as solutions are enantiomorphic
>>>>>> Best Solution space group P 41 21 2
>>>>>>
>>>>>> ... is that b/c pointless can only report one, and SG92 came up
>>>>>> first?
>>>>>>
>>>>>> -bryan
>>>>>
>>>>>
>>>>
>>>
>>>
>>
>>
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