NAME

PARAMETERS

input filename

This is simply the input file/stream name, i.e., where the rays are coming from.

tag filename

The tag parameter gives the name of the rdb files in which the ph_survey3 results will be written. (Actually, the filenames will be tag _res and tag _res2, the second file being a summary of the first). The rdb _res file will contain the determined beam center and required number of iterations for each beam-center run which ph_survey3 performs, and the _res2 file will contain the average center for all of the runs of a given parameter combination, along with a (radial) rms spread value and the average required number of iterations in beam-center.

xinit real

This is the x-coordinate of the location where the user wishes the ph_survey3 program to start, i.e., in all of the beam-center runs made using the first (and largest) pinhole diameter, the pinholes will be centered around this x-value. For other pinhole diameters, the pinholes will be centered at the beam's center as determined by the set of runs immediately preceding it.

yinit real

Same as xinit, except in reference to the y-coordinate.

photdens real

This is merely a ``database parameter'', i.e., one that is not necessary for the ph_survey3 module itself, but which provides information about the input rays which could be useful in the database. For instance, by specifying the photon density explicitly, the same ph_survey3 run can be performed on ray streams which only differ in photon density, and the database can thus keep records on both runs, and distinguish between them (rather than simply erasing the old data). The photon density should be provided in counts per square millimeter, for clarity.

shell integer

This is another ``database parameter'', which specifies which shell the incoming rays were reflected from. (Please see photdens for my ``definition'' of a ``database parameter'').

numrand integer

This parameter tells ph_survey3 how many different "random initial coordinate" runs it should make for each parameter combination, in order to accurately and efficently determine the center of the beam.

version boolean

If set to yes, simply print the version and die.

debug string

This parameter gives the user the option of setting various debug flags in the beam-center module.

mode string

This specifies which parameter mode ph_survey3 is to be run in. As of now, the only mode is ``a'' mode.

DESCRIPTION

First of all, as is explained in the beam-center documentation, when large pinholes are being used for scans (i.e., diameters greater than 150 microns), the pinholes are too large (in comparison with the beam size) for there to be an accurate determination of the beam's center. In order to correct this problem, the beam is projected to an image plane slightly out of focus, forming a small ring. Ideally, the size of this ring should be slightly smaller than the pinholes which are scanning it, since we don't want to sample only the center of the ring (which is what would occur if the ring was somewhat larger than the pinhole diameter). The question that needed to be answered for this ``big pinhole'' survey was this: What fraction of the pinhole diameter should the ring diameter be? In hopes of helping to answer this question, the ph_survey2 module was modified so that this ``ring fraction'' parameter could be varied, along with the pinhole diameter, number, and spacing. This meant that a set of ring fractions had to be added, and another loop nested around the call to beam-center. Furthermore, the two databases had to be modified so that they contained a column specifying this ringfract parameter for each entry. The call to beam-center was altered so that the project parameter was always set to 'ring', and the tma_defaults option turned on. Of course, the ringfract parameter now also needed to be passed in to beam-center as well.

There is one other change which was implemented in the ph_survey3 code, which allowed all of the .centlog files from the beam-center runs to be stored under names carrying unique extensions (which included the numerical values for the pinhole diameter, spacing, and number, and the ring fraction). This particular feature has no particular relevance to the ``big pinhole survey'' -- in fact, it should probably have been implemented as an option in the other two ph_survey modules as well, (and changed to an option instead of a mandate in the ph_survey3 module).

AUTHOR