The Fiber Common Block

typedef struct FIBER_COM {
  int   id,ixy,isc,ish,ifib,iitn;
  int   hitweight;
  int   npix;
  int   nclus;
  int   tadc;
  float ccdpos[2],ccdrad[2],rspos[2][3];
  int   iic[MAX_DAUGHTER_CLUS];
  float iicw[MAX_DAUGHTER_CLUS];
  int   pix[MAX_DAUGHTER_PIX];
  float pixw[MAX_DAUGHTER_PIX];
} FIBER_COM;

       common/fgfib/fgfib_id,fgfib_ixy,fgfib_isc,fgfib_ish,
     &            fgfib_ifib,fgfib_iitn,
     &            fgfib_hw,
     &            fgfib_hnp,fgfib_hnc,
     &            fgfib_hta,
     &            fgfib_ccdpos,fgfib_ccdrad,fgfib_rspos,
     &            fgfib_iic,fgfib_iicw,
     &            fgfib_pix,fgfib_pixw

The Fiber common block is the fundamental unit of information about a single fiber.

Every fiber has a unique "id" number. id is a 32-bit (4 byte) integer. The most significant byte is set to the IIT number to which the fiber is attached, the next byte is the sheet number, followed by the fiber number in the two least significant bytes. In C, this is denoted as $((iitn<<24)\vert(isc<<16)\vert(ifib))$.

The next four variables, ixy, isc, ish, and ifib, are the coordinates of the fiber within the detector structure. ixy is 1 if the fiber is an "X" fiber, and 2 if it is a "Y" fiber. isc is the "section" (or layer) number. A section consists of all fibers between adjacent water target layers. Sections are numbered from 1 to 20. ish is the sheet number. Each section is composed of 12 sheets, six in X and six in Y. Sheets are numbered from 1 to 6. ifib is the fiber number. Every fiber in a sheet is assigned a unique number from 1 to 1142. iitn is the number of the IIT to which this fiber is attached. This variable is redundant, since may be inferred from ixy, ish, and isc, but it is provided for convenience.

hitweight is the strength of the hit, in arbitrary units. hitweight is 0 if the fiber is not hit, and non-zero otherwise.

If the fiber is hit, npix will be set equal to the number of CCD pixels associated with the fiber, and nclus will contain the number of associated pixel clusters. Not all hit finding algorithms associate fibers with pixels or clusters, so these fields may be zero, even if the fiber is hit.

tadc is the "total adc" for the fiber hit. tadc may or may not be equal to hitweight.

ccdpos, ccdrad, and rspos are the coordinates of the fiber. The first element of ccdpos is the CCD X coordinate; the second is the CCD Y coordinate. ccdrad contains the X and Y radii of the ccd image of the fiber in units of pixels. rspos contains the coordinates of the fiber in real space. rspos is composed of two three-vectors. Each three-vector corresponds to an endpoint of the fiducial region of the fiber, specified in units of mm, in the detector hall coordinate system.

The remaining elements are the so called "daughter lists". When a fiber is marked as hit, this hit may be associated with pixels or clusters of pixels by the hit finding algorithm. If these associations are made, the ID numbers for the pixels/clusters are placed in the pix/ iic lists. Each of these daughter elements also has associated with it a "weight". Each weight is a floating point number in the range of 0 to 1, with a 1 representing complete membership, and a fractional number representing partial membership. For example, a pixel which is on the boundary of a fiber region may be given a fractional weighting. A weight of 0 is nonsensical. The number of elements in each of these lists is recorded in npix and nclus.