The files generated by XDS are either ASCII type files that can be inspected and modified by using a text editor, or binary, compressed image files that can be looked at using the XDS-Viewer program.
All files have a fixed name defined by XDS, which makes it mandatory to process each data set in a newly created directory to avoid name clashes. Clearly, one should not run more than one XDS-job simultaneously in the same directory.
Rotation data images are processed in 8 steps which are called in succession by XDS. Results and diagnostics from each step are documented in files with the name extension .LP for inspection by the user. Information between the steps is exchanged by files, which allows repetition of selected steps with a different set of input parameters without rerunning the whole program. Note, that by rerunning a processing step the earlier version of the output files from this step will be overwritten. Thus, these older files should first be given another name if their original contents are meant to be saved.
|xds step||input files||output files|
This file contains the input parameters you have to provide to run XDS.
Each parameter name consists of a string of characters without intervening blanks or exclamation marks and includes an equal sign as its last character. The parameter value must directly follow the parameter name and be on the same line. The parameter names cannot be abbreviated; they are case sensitive, too. The parameters may be given in arbitrary order. Characters in a line to the right of an exclamation mark are comment.
The file XDS_ASCII.HKL contains the result of data processing by XDS,
namely the corrected intensities of all reflections recorded in the
Output files generated by xscale adopt a similar layout but are named as defined by the user.
The file consists of a header, reflection data records, and a line marking the end of the data. Each line is at most 132 characters in length. The data records consist of a fixed number of numerical items that are separated by at least one blank. Header lines and the terminator line are distinguished from the reflection data records by the presence of the exclamation mark symbol '!'.
The last line of the header is identified by !END_OF_HEADER
The file (type ASCII) contains a list of strong observed diffraction spots that is generated by the "COLSPOT" step. Information about a spot is saved as a single line containing the items x,y,z,Intensity,iseg. The items are separated by at least one blank character.
The file is read subsequently by
"IDXREF" and indices are attached to each spot. Indices 0 0 0
are used to indicate a spot that could not be indexed. On return, the
original file contents is replaced by records
for each spot, where h,k,l are the reflection indices. Item iseg is only present if the detector contains more than one segment.
Each file contains all diffraction parameters necessary for computing the locations of all reflections occuring in the data images.
An initial set of parameters is determined by "IDXREF" and saved on file XPARM.XDS. A final set of parameters is computed by "CORRECT" and saved on file GXPARM.XDS. Both files are of identical format, the meaning of the parameters is as described below. In case a better solution has been obtained from the refinements in the "CORRECT" step, one could replace XPARM.XDS by GXPARM.XDS and rerun "INTEGRATE" and "CORRECT". Usually this is not necessary, but this possibility may be useful in certain critical cases. NOTE that GXPARM.XDS will not exist in case the global refinements in the "CORRECT" step were unsuccessful.
The file comprises 11 lines of data values that code for
Now, for each detector segment the following two lines of information are provided.
This file contains the results from the INTEGRATE step. The file begins
with a self-explaining header. Each header record starts with a '!'.
The last header record is indicated by !END_OF_HEADER. The maximum length
of a header line is at most 512 characters which is sufficient to
accommodate long path names of the image directory.
The reflection records follow immediately after the header. A terminator record, !END_OF_DATA, follows the last reflection record.
Each reflection record consists of 21 numerical data items
h, k, l, IOBS, SIGMA, XCAL, YCAL, ZCAL, RLP, PEAK, CORR, MAXC, XOBS, YOBS, ZOBS, ALF0, BET0, ALF1, BET1, PSI, ISEG
that are output as a single line not longer than 200 characters. The numerical items are separated by a blank and can be read in free-format.
This compressed file contains the last data image processed in the INTEGRATE step enriched with ellipsoids around all expected diffraction spots. The user is strongly encouraged to have a look at this image. The clearly visible spots in this control image should appear encircled, centered near the spot maximum (reflections close to the rotation axis are not integrated). Often, problems in data processing become immediately obvious by looking at this control image.
In the CORRECT step, XDS checks for the presence of a file named FILTER.HKL in the current directory. A file of this name can be provided by the user to specify reflections on file INTEGRATE.HKL that should be ignored in the CORRECT step and thus be excluded from the final output file XDS_ASCII.HKL. Typically, FILTER.HKL is generated by a special user program to handle complicated experimental situations in which parts of the detector become obscured.
Each reflection record of the file FILTER.HKL consists of 9 numbers
with at least one blank character between them (free format record)
H K L X Y Z DX DY DZ.
H K L are the integer reflection indices,
X Y are the location (pixel units) in the segment plane of the detector where the reflection is expected to be recorded,
Z is the expected running number of the image containing the Bragg peak,
DX DY DZ are dimensions of the target area around X Y Z used for decision making.
A reflection record h k l XCAL YCAL ZCAL on INTEGRATE.HKL will be ignored if there exists at least one record on file FILTER.HKL so that all of the relations are satisfied
h=H, k=K, l=L, |XCAL-X|<DX, |YCAL-Y|<DY, |ZCAL-Z|<DZ
In the CORRECT step, XDS checks for the presence of a file named REMOVE.HKL in the current directory. A file of this name can be provided by the user to specify the indices of reflections that should be excluded from the final output file XDS_ASCII.HKL. Each reflection record of this file consists of the reflection indices h, k, l and possibly other information that will be ignored. Up to 10000 reflections can be specified.
Reflections that do not obey Wilson's statistic often arise from ice rings in the data images. These outliers are reported near the end of the file CORRECT.LP. To suppress the unwanted reflections from the final output file XDS_ASCII.HKL, the user copies them to a file named REMOVE.HKL in the current directory and repeats the CORRECT step (grep alien CORRECT.LP > REMOVE.HKL). NOTE, that for the repeat run space group number and cell constants must be provided so that the indices listed in REMOVE.HKL are consistent!
The files X-CORRECTIONS.cbf and Y-CORRECTIONS.cbf are generated by the
XYCORR step of XDS and contain look-up tables to correct the X and Y pixel
positions on the detector for spatial distortions. The spatial
corrections for a pixel at IX,IY (0<IX<=NX, 0<IY<=NY) are
found in the tables at address IA4=IX4+NXBY4*(IY4-1) where
IX4=1+(IX-2)/4, IY4=1+(IY-2)/4, and NXBY4= 1+(NX-2)/4, such that the
corrected pixel-coordinates are
The other files are generated by the CORRECT step of XDS. All of the files can be visualized using the XDS-Viewer program. The spatial corrections reported by clicking the left mouse button are in pixel units multiplied by 10.
The files DX-CORRECTIONS.cbf and DY-CORRECTIONS.cbf show systematic discrepancies between observed and calculated spot locations. Such systematic discrepancies could result from the use of incorrect look-up tables X-CORRECTIONS.cbf, Y-CORRECTIONS.cbf during data processing.
The files GX-CORRECTIONS.cbf and GY-CORRECTIONS.cbf consist of the original look-up tables (X-CORRECTIONS.cbf, Y-CORRECTIONS.cbf) plus the systematic discrepancies (DX-CORRECTIONS.cbf, DY-CORRECTIONS.cbf). To salvage the data set, the new look-up tables (GX-CORRECTIONS.cbf, GY-CORRECTIONS.cbf) can be renamed by the user to replace the original files X-CORRECTIONS.cbf, Y-CORRECTIONS.cbf and a complete data processing (with the exception of the XYCORR step) can be carried out.
BLANK.cbf contains the dark current (non-Xray) background. The dark
current for a pixel at IX,IY (0<IX<=NX, 0<IY<=NY) is found
at address IA4=IX4+NXBY4*(IY4-1) in the table, where
IX4=1+(IX-2)/4, IY4=1+(IY-2)/4, and NXBY4= 1+(NX-2)/4.
GAIN.cbf contains the ratio between variance and mean of the pixel contents in the neighbourhood of each image pixel. The table is used for classifying data image pixels into background or spot.
These files contain an image of the INTEGER array IBKG(NX*NY) such that IBKG(IX+NX*(IY-1)) is the background value at pixel position IX,IY (0<IX<=NX,0<IY<=NY). NX,NY are the number of pixels along the detector X- and Y-axis. (IX is the fast index.)
BKGINIT.cbf is generated in the INIT step and serves as input of the DEFPIX step. DEFPIX recognizes shaded regions in the background table BKGINIT.cbf and removes them from the set of trusted pixels. Untrusted pixels are marked by -3.
BKGPIX.cbf is the background table resulting from the DEFPIX step. It serves as starting background table for the INTEGRATE step.
This file contains an image of the INTEGER array IFRAME(NX*NY) such that IFRAME(IX+NX*(IY-1)) is the ratio between the background at IX, IY and the mean background for all pixels of the same resolution, multiplied by 10000. NX,NY are the number of pixels along the detector X- and Y-axis. (IX is the fast index.) This file is generated in the DEFPIX step of XDS and should be inspected by the user with the XDS-Viewer program. The image clearly shows shaded regions of the detector that should be removed from the trusted detector area. Pixels in the shaded region have a value below 10000, and in case the default setting was unsatisfactory, the user may change the input parameter VALUE_RANGE_FOR_TRUSTED_DETECTOR_PIXELS= and repeat the DEFPIX step. As a result from the DEFPIX step the initial pixel background table BKGPIX.cbf will be obtained with untrusted pixels marked by -3.
This file, generated in the CORRECT step of XDS, contains an image of the correction factors applied to the reflection intensities as function of image number and detector region of their recorded Bragg peaks. The correction factors are multiplied by 1000 and saved in the file ABSORP.cbf as a CBF-compressed INTEGER array(IX+NX*(IY-1)), with NX "fast" pixels (IX=1,NX; along image numbers) running from left to right and NY "slow" pixels (IY=1,NY; enumerating the detector regions) pointing upwards. This file is meant to be inspected by the user with the XDS-Viewer program and replaces the numerical print-out within CORRECT.LP of previous versions of XDS.
This file, generated in the CORRECT step of XDS, contains an image of the correction factors applied to the reflection intensities as function of image number and resolution of their recorded Bragg peaks. The correction factors are multiplied by 1000 and saved in the file DECAY.cbf as a cbf-compressed INTEGER array(IX+NX*(IY-1)), with NX "fast" pixels (IX=1,NX; along image numbers) running from left to right and NY "slow" pixels (IY=1,NY; along (2*sin(theta)/lamda)^2) pointing upwards. This file is meant to be inspected by the user with the XDS-Viewer program and replaces the numerical print-out within CORRECT.LP of previous versions of XDS.
This file, generated in the CORRECT step of XDS, contains an image of the correction factors applied to the reflection intensities as function of the detector coordinates of their recorded Bragg peaks. The correction factors are multiplied by 1000 and saved in the file MODPIX.cbf as a cbf-compressed INTEGER array(IX+NX*(IY-1)), with NX "fast" pixels (IX=1,NX; along the detector's X-direction) running from left to right and NY "slow" pixels (IY=1,NY; along the detector's Y-direction) pointing upwards. This file is meant to be inspected by the user with the XDS-Viewer program and replaces the numerical print-out within CORRECT.LP of previous versions of XDS.
© 2009-2018, MPI for Medical Research, Heidelberg