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Indexing: Difference between revisions
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Please also see [[IDXREF.LP]] ! | |||
== Indexing images from non-merohedrally twinned crystals (i.e. several lattices) == | == Indexing images from non-merohedrally twinned crystals (i.e. several lattices) == | ||
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* just because XDS decides not to use some spots for indexing doesn't mean these initially non-indexed spots really belong to a separate lattice: compare the indexing/orientation matrices for the different solutions to see if they are significantly different (e.g. related by a one degree rotation). Also, check your images visually (ideally with the predictions on top) to make sure you acrtually have several lattices. | * just because XDS decides not to use some spots for indexing doesn't mean these initially non-indexed spots really belong to a separate lattice: compare the indexing/orientation matrices for the different solutions to see if they are significantly different (e.g. related by a one degree rotation). Also, check your images visually (ideally with the predictions on top) to make sure you acrtually have several lattices. | ||
* the refinement of parameters (during the INTEGRATE step) can be very unstable: often, the spots of the two (or more) lattices are very close together: during data collection, some orientations of the spindle axis might make them move even closer until full overlap. At that point (or shortly after) the parameter refinement might 'jump' into the wrong lattice by chance. So look out for any jumps in parameters (distance, detector origina, scale, mosaicity etc), or prevent refinement of orientation in INTEGRATE altogether (REFINE(INTEGRATE)= without parameters). | * the refinement of parameters (during the INTEGRATE step) can be very unstable: often, the spots of the two (or more) lattices are very close together: during data collection, some orientations of the spindle axis might make them move even closer until full overlap. At that point (or shortly after) the parameter refinement might 'jump' into the wrong lattice by chance. So look out for any jumps in parameters (distance, detector origina, scale, mosaicity etc), or prevent refinement of orientation in INTEGRATE altogether (REFINE(INTEGRATE)= without parameters). | ||
== Finding out the angular difference between two lattices == | |||
This can be easily found with "cmpmat" from [http://www.globalphasing.com/autoproc/ GlobalPhasing's autoPROC] package. | |||
cmpmat 01/XPARM.XDS 02/XPARM.XDS P212121 | |||
would compare the orientations stored in 01/XPARM.XDS and 02/XPARM.XDS (assuming both were determined for space group P212121), and return the lowest angular difference from all combinations of symmetry-related crystal setting matrices. | |||
cmpmat 01/XPARM.XDS 02/XPARM.XDS P212121 -2 | |||
would return ''all'' angular differences, for ''all'' pairs of symmetry-related crystal setting matrices. | |||