SAXS parameter file

All processing and utility programs in the SAXS system rely on a detector parameter file, although only some parameters are used by any given program. The parameter file can be modifying using any text editor.

While the current system uses data files written by the Raxis-!V system, data collected on some other systems (e.g., Hamlin detectors) can also be processed by modifying the parameter file appropriately.

Parameter file example

      3000	          (1) number of USHORTS in file header
      3000 3000           (2) pixels in the fast & slow direction
      1 	          (3) beamstop type
      1266 488 958 988    (4) beamstop line 1 or LL,UR crnrs (pxls)
      1002 988 1358 560   (5) beamstop line 2
      0.100000 0.100000   (6) mm/pixel in fast, slow directions
      740.000000          (7) sample - detector distance in mm
      150.0 150.0         (8) Refined center in mm.
      0.02 0.10 0.005	  (9) Smin Smax Sdel
      1.5418             (10) wavelength in angstroms
    

Parameter file format

The parameter file has 10 lines, with one or more parameter on each line. All parameters on a line are separated by spaces. The lines are in a fixed order. All lines must be present, and all required parameters must be present on each line.

On each line, anything after the last parameter is ignored. This allows the parameter file to be annotated, as shown in the example.

joy

top of page

example

format

parameters

beamstop

Parameters -- details

1. number of USHORTS in file header -- Data files consist of a header, followed by data. This is the number of USHORTS in the header, where a USHORT is a 2-byte integer.
2. pixels in the fast & slow direction -- The data portion of the image file consists of NSLOW rows, each containing NFAST data points or pixels. In the Raxis-IV system, the fast direction goes from left to right, while the slow direction goes from bottom to top. Each pixel is a USHORT, which is an unsigned, 2=-byte integer.
3. beamstop type -- Allowable types ae 0 (no beamstop), 1, or 2. For details see below.
4. beamstop line 1 or LL,UR crnrs (pxls) -- fast1 slow1 fast2 slow2 -- the endpoints in pixel coordinates of a line defining the beamstop. This has a different meaning for type 1 or type 2 (see below. For type 0, the 4 coordinates are ignored but must be present.
5. beamstop line 2 -- Coordinates as for line 1. Used only for type 1 (see below. For type 0 or 2, the 4 coordinates are ignored but must be present.
6. mm/pixel in fast, slow directions
7. sample - detector distance in mm
8. Refined center in mm. -- Coordinates of the beam center.
9. Smin Smax Sdel -- Limits and bin size for radial averaging.
10. wavelength in angstroms

Specifying the beamstop avoid box parameters

When collecting data, the beamstop and its support cast a shadow on the detector. Data points within that shadow should be excluded from calculation. There are three ways to specify the beamsto avoid box in the parameter file. These are understood by the processing program savage, and the utility program beamtest.

• Type 0 means no beamstop -- process all data points. (beamstop lines 1 and 2 must be specified in the parameter file, but their values will be ignored).
• Type 1 -- The next two parameters (line 1 and line 2) specify the endpoints of two lines defining the avoid box. Each endpoint is in (fast,slow) order in pixel coordinates. The lines are extended out to the edge of the detector, and all data points between the lines are excluded from calculation.
• Type 2 -- The next parameter (line 1) specifies the (fast,slow) pixel coordinates of the lower left and upper right corner of a rectangle, which will constitute the avoid box. All data points within the rectangle will be excluded. Beamstop line 2 must be specified in the parameter file, but its values will be ignored).

Last Modified: Friday, 15-Oct-2004 16:18:00 EDT