# IDXREF.LP

IDXREF.LP is the logfile of the IDXREF "job". It reports on aspects of the analysis of difference vectors, the lattice(s) encountered, their interpretation in terms of 44 Bravais lattices, and the refinement of all geometric parameters of the experiment based on the strong reflections identified in the SPOT_RANGE by COLSPOT.

In the following, extracts from a typical IDXREF.LP are shown, together with comments, in the order as they occur.

## Listing of parameter values used for indexing

INPUT PARAMETER VALUES
----------------------
NAME_TEMPLATE_OF_DATA_FRAMES=../kb/G3-16mer-A2-1_1_???.img TIFF
STARTING_ANGLE=        0.0000     STARTING_FRAME=       1
NX=  3072  NY=  3072    QX=  0.073242  QY=  0.073242
ROTATION_AXIS=  1.000000  0.000000  0.000000
OSCILLATION_RANGE=    1.0000
X-RAY_WAVELENGTH=       1.000000
INCIDENT_BEAM_DIRECTION=  0.000000  0.000000  1.000000
DIRECTION_OF_DETECTOR_X-AXIS=   1.00000   0.00000   0.00000
DIRECTION_OF_DETECTOR_Y-AXIS=   0.00000   1.00000   0.00000
DETECTOR_DISTANCE=   349.994
ORGX=   1532.00  ORGY=   1566.00
INDEX_MAGNITUDE=   8    INDEX_ERROR=   0.050    INDEX_QUALITY=  0.80
MAXIMUM_ERROR_OF_SPOT_POSITION=   3.0
MAXIMUM_ERROR_OF_SPINDLE_POSITION=   2.0
SPACE GROUP AND CELL PARAMETERS ARE UNKNOWN


The values shown are taken from XDS.INP, or if not given there, the defaults are output. "SPACE GROUP AND CELL PARAMETERS ARE UNKNOWN" means that XDS.INP had SPACE_GROUP_NUMBER=0

## Which data were used for indexing?

AUTOINDEXING IS BASED ON   4043 SPOTS
LOCATED IN THE TRUSTED_REGION= 0.00 1.20 OF THE DETECTOR
OF THE FOLLOWING DATA IMAGES:
SPOT_RANGE=       1      90


The "SPOTS" mentioned above are read from SPOT.XDS, and are collected by COLSPOT. Nota bene: SPOT.XDS is a text file and could be written by a custom program, or a SPOT.XDS written by COLSPOT could be modified afterwards - see Indexing!

## Determination of the reciprocal lattice basis

NUMBER OF DIFFERENCE VECTOR CLUSTERS USED                     198
MAXIMUM RADIUS OF DIFFERENCE VECTOR CLUSTERS (pixels)   3
MINIMUM DISTANCE BETWEEN DIFFRACTION SPOTS (pixel)    6.0
MINIMUM ALLOWED DISTANCE BETWEEN REC. LATTICE POINTS   0.1256E-02
OBSERVED BASIS CELL VOLUME                             0.1080E+07
DIMENSION OF SPACE SPANNED BY DIFFERENCE VECTOR CLUSTERS   3

#  COORDINATES OF REC. BASIS VECTOR    LENGTH   1/LENGTH

1   0.0040197-0.0034658 0.0044763  0.0069432     144.03
2   0.0060960 0.0063989-0.0005531  0.0088551     112.93
3  -0.0064850 0.0072590 0.0114902  0.0150590      66.41


Above, the values of CLUSTER_RADIUS (3) and SEPMIN (6.0) are repeated. The reciprocal cell axis lengths (given as 1/LENGTH) are derived from the difference vectors between reciprocal lattice points. If the user supplies UNIT_CELL_CONSTANTS (and SPACE_GROUP_NUMBER is >0), then the supplied unit cell axes are matched here against the observed difference vectors.

The output continues with showing the difference vectors in h,k,l units - ideally these should be close to integral numbers (1, 2 3, ...), which they are in this example:

CLUSTER COORDINATES AND INDICES WITH RESPECT TO REC. LATTICE BASIS VECTORS

#  COORDINATES OF VECTOR CLUSTER   FREQUENCY       CLUSTER INDICES
1 -0.0040208 0.0034733-0.0044142      991.     -0.99      0.00      0.00
2 -0.0101816-0.0029195-0.0037781      945.     -0.99     -1.01      0.01
3 -0.0122581-0.0127817 0.0012276      937.      0.00     -2.00      0.01
4 -0.0061055-0.0064076 0.0006063      921.      0.00     -1.00      0.00
5 -0.0020733-0.0098616 0.0050198      904.      1.00     -1.00      0.00
6 -0.0080465 0.0069232-0.0089221      848.     -2.00      0.00      0.00
7 -0.0141979 0.0005603-0.0082059      844.     -1.99     -1.00      0.01
8  0.0064218-0.0072694-0.0114905      801.      0.00     -0.01     -1.00
9 -0.0019301 0.0133409-0.0094462      794.     -1.99      1.00      0.00
10 -0.0206410 0.0078000 0.0032924      757.     -1.98     -1.00      1.01
11 -0.0203128-0.0058325-0.0075707      744.     -1.98     -2.01      0.02
12 -0.0023531 0.0037679 0.0159009      740.      1.01      0.01      0.99
...
58  0.0000713 0.0231797-0.0145601      486.     -3.01      1.99      0.00
59 -0.0119425-0.0263910-0.0096567      482.      0.00     -3.01     -0.99
60 -0.0117272-0.0032032-0.0242257      480.     -3.00     -1.00     -0.99

PARAMETERS OF THE REDUCED CELL (ANGSTROEM & DEGREES)
66.41    112.93    144.03     89.86     89.89     89.76

#  COORDINATES OF REC. BASIS VECTOR    REDUCED CELL INDICES

1   0.0040197-0.0034658 0.0044763     0.00    0.00    1.00
2   0.0060960 0.0063989-0.0005531     0.00    1.00    0.00
3  -0.0064850 0.0072590 0.0114902    -1.00    0.00    0.00


From the difference vectors, the "reduced cell" (essentially a P1 cell, with a<b<c) has been established, together with its axes and angles. Furthermore the relation of the reciprocal cell axes (found in the beginning) with respect to the reduced cell is given. If the user supplies UNIT_CELL_CONSTANTS (and SPACE_GROUP_NUMBER >0 ) then these are converted to a reduced cell and given here.

## Results from local indexing

RESULTS FROM LOCAL INDEXING OF   3000 OBSERVED SPOTS *****

MAXIMUM MAGNITUDE OF INDEX DIFFERENCES ALLOWED    8
MAXIMUM ALLOWED DEVIATION FROM INTEGERAL INDICES     0.050
MIMINUM QUALITY OF INDICES FOR EACH SPOT IN A SUBTREE    0.80
QUALITY OF INDICES REQUIRED TO INCLUDE SECOND SUBTREE    0.00
NUMBER OF SUBTREES    118

SUBTREE    POPULATION

1         2873
2            6
3            3
4            2
5            2
6            2
...


The "subtrees" each refer to their own lattice. The list above indicates that 2873 out of the strongest 3000 reflections can be indexed with a single lattice. 6 reflections correspond to the second-best lattice. If the diffraction pattern arises from split crystals, or there are two (or more) non-equivalent lattices because e.g. ORGX ORGY (in XDS.INP) denote a position right in the middle between two reflections, then several lattices are listed here that have a substantial number of reflections. In such a case IDXREF will choose the lattice with most reflections, but the user should be aware that other lattices exist!

## Finding the origin of the reciprocal lattice (=direct beam position, if normal geometry)

***** SELECTION OF THE INDEX ORIGIN OF THE REFLECTIONS *****
The origin of the reflection indices determined so far is
0,0,0 by default which is usually correct. In certain critical
cases it may happen that this automatic choice is wrong which
leads to misindexing of the reflections by a constant offset.
You may replace the default by specifying INDEX_ORIGIN= h k l
in the input file "XDS.INP" and rerun the IDXREF step.
Below you find a list of possible alternatives together with a
measure of their likelihood.
QUALITY   small values mean a high likelihood for this offset
DELTA     distance between given  1532.00  1566.00 and computed
direct beam position (pixels) on the detector
XD, YD    computed direct beam position (pixels) on detector
X,Y,Z     computed coordinates of the direct beam wave vector
DH,DK,DL  mean absolute difference between observed and
fitted indices

INDEX_   QUALITY  DELTA    XD       YD       X       Y       Z       DH      DK      DL
ORIGIN

0  0  0      1.0    0.5   1531.7   1566.3 -0.0001  0.0001  1.0000    0.06    0.06    0.10
0  0 -1      4.4   30.4   1550.9   1542.1  0.0039 -0.0050  1.0000    0.13    0.11    0.16
0  0  1      4.4   31.4   1512.4   1590.6 -0.0041  0.0051  1.0000    0.13    0.11    0.15

SELECTED:     INDEX_ORIGIN=  0  0  0


Errors in the values of ORGX, ORGY (as supplied in XDS.INP) are the most common single source of indexing failure. XDS tries several possible origins (3 in the example above) around the supplied values and gives an estimate of indexing quality ("QUALITY"; 1.0 is best) for each of them. DH,HK,DL should ideally be 0; they correspond to the deviation of H,K,L from being integer. It is advisable to always use INDEX_ORIGIN= 0 0 0 (the default); if the QUALITY and DH,DK,DL indicators say that the supplied ORGX, ORGY are wrong then the latter should be fixed.

It is important to realize that ORGX and ORGY are the coordinates of the point of the detector which is closest to the crystal; this is not the same as the direct beam coordinates! However, in practice, at synchrotron beamlines the detector is perpendicular to the beam, in which case taking the direct beam position as ORGY ORGY is accurate enough; IDXREF (and INTEGRATE, CORRECT) refines the beam direction (and other geometric parameters) anyway. This is also why there is no need to specify highly accurate values for BEAM_DIRECTION, ROTATION_AXIS, ORGX, ORGY.

The word "SELECTED:" may be a bit misleading - XDS does not select the INDEX_ORIGIN, it's the user who does this.

## First refinement of geometry parameters

***** REFINED SOLUTION BASED ON INDEXED REFLECTIONS IN SUBTREE # 1 *****

REFINED VALUES OF DIFFRACTION PARAMETERS DERIVED FROM   2873 INDEXED SPOTS
REFINED PARAMETERS:   DISTANCE BEAM AXIS CELL ORIENTATION
STANDARD DEVIATION OF SPOT    POSITION (PIXELS)     5.16
STANDARD DEVIATION OF SPINDLE POSITION (DEGREES)    4.60
CRYSTAL MOSAICITY (DEGREES)     0.200
DIRECT BEAM COORDINATES (REC. ANGSTROEM)  -0.002368  0.008316  0.999963
DETECTOR COORDINATES (PIXELS) OF DIRECT BEAM    1531.82   1565.97
DETECTOR ORIGIN (PIXELS) AT                     1541.74   1531.14
CRYSTAL TO DETECTOR DISTANCE (mm)       306.77
LAB COORDINATES OF DETECTOR X-AXIS  1.000000  0.000000  0.000000
LAB COORDINATES OF DETECTOR Y-AXIS  0.000000  1.000000  0.000000
LAB COORDINATES OF ROTATION AXIS  0.999916 -0.012791 -0.002291
COORDINATES OF UNIT CELL A-AXIS    24.214   -28.552   -44.997
COORDINATES OF UNIT CELL B-AXIS    68.543    70.993    -7.718
COORDINATES OF UNIT CELL C-AXIS    74.857   -62.751    80.778
REC. CELL PARAMETERS   0.017084  0.010103  0.007889  90.239  89.766  89.803
UNIT CELL PARAMETERS     58.534    98.983   126.753  89.760  90.235  90.198
SPACE GROUP NUMBER      1


Based on the parameters known at this point, and all reflections assigned to the strongest lattice, a first refinement is done.

## Second refinement, after rejecting reflections that do not fit well

***** INDEXING OF OBSERVED SPOTS IN SPACE GROUP #   1 *****
1103 OUT OF    4043 SPOTS INDEXED.
0 REJECTED REFLECTIONS (REASON: OVERLAP)
2940 REJECTED REFLECTIONS (REASON: TOO FAR FROM IDEAL POSITION)
EXPECTED ERROR IN SPINDLE  POSITION     0.809 DEGREES
EXPECTED ERROR IN DETECTOR POSITION      1.90 PIXELS

***** DIFFRACTION PARAMETERS USED AT START OF INTEGRATION *****

REFINED VALUES OF DIFFRACTION PARAMETERS DERIVED FROM   1103 INDEXED SPOTS
REFINED PARAMETERS:   DISTANCE BEAM AXIS CELL ORIENTATION
STANDARD DEVIATION OF SPOT    POSITION (PIXELS)     1.86
STANDARD DEVIATION OF SPINDLE POSITION (DEGREES)    0.79
CRYSTAL MOSAICITY (DEGREES)     0.200
DIRECT BEAM COORDINATES (REC. ANGSTROEM)   0.002112  0.014343  0.999895
DETECTOR COORDINATES (PIXELS) OF DIRECT BEAM    1531.92   1565.77
DETECTOR ORIGIN (PIXELS) AT                     1522.67   1502.92
CRYSTAL TO DETECTOR DISTANCE (mm)       320.89
LAB COORDINATES OF DETECTOR X-AXIS  1.000000  0.000000  0.000000
LAB COORDINATES OF DETECTOR Y-AXIS  0.000000  1.000000  0.000000
LAB COORDINATES OF ROTATION AXIS  0.999918 -0.009393 -0.008744
COORDINATES OF UNIT CELL A-AXIS    25.289   -29.852   -46.602
COORDINATES OF UNIT CELL B-AXIS    71.309    74.418    -8.739
COORDINATES OF UNIT CELL C-AXIS    78.373   -65.138    84.444
REC. CELL PARAMETERS   0.016435  0.009668  0.007556  90.014  89.938  89.901
UNIT CELL PARAMETERS     60.847   103.437   132.348  89.986  90.062  90.099
SPACE GROUP NUMBER      1


Based on the results from the first refinement, all reflections found by COLSPOT are indexed. In this case, a bit more than 1/4 of these are indexed with low error. This leads to the message "!!! ERROR !!! INSUFFICIENT PERCENTAGE (< 50%) OF INDEXED REFLECTIONS" at the bottom of IDXREF.LP .