We have made extensive use of the CTD offline proto-type software package ARAXNE [11]. It provides utilities and a framework for the development of CTD pattern recognition software. The package uses an extensive data structure realised in BOS [12].
The link between ARAXNE and the SLT pattern recognition routines is a package of subroutines called DSREAD [14] (see figure 3). The interface to the ARAXNE software is via the BOS data structures that have been defined for the offline proto-type pattern recognition software [12]. The DSREAD package is designed to be used in place of the offline segment finding routines in the ARAXNE main program. Hence combinations of online segment finding with offline track finding code can be run or visa versa, and compared with running pure online or offline code. These runs will not be presented in this note.
The DSREAD structure was written to reflect the CTD-SLT processing architecture. This will ease the movement of the SLT algorithm out of the ARAXNE-BOS framework into the offline environment.
The following stages of processing are performed by the DSREAD package before segment finding.
The first steps allow the chamber occupancy to be assessed and a suitable region chosen to form the pattern recognition mask. At the moment a single-cell masks is used. The pre-processing of the SLT data is meant to represent the functions the DSP would perform after pulse analysis. At present pre-processing performs two operations: (i) all drift times are multiplied by a scale factor (100) and converted to integers, and (ii) hits on the same wire are re-ordered in increasing drift time. Eventually we will also require the DSP to apply drift time corrections, assign quality flags, and perform hit rejection. Reference [3] gives more details of the DSP output data format.
Routines can then be called to perform segment pattern recognition within the current mask. These are the online segment finding routines used for the studies presented in this note. These routines will be used by the CTD SLT and will be coded in occam and run on a system of transputers.
The next task performed by DSREAD is post-processing, which is performed in the following stages.
At present the segment parameters constitute the gradient, slope, and errors in LNO co-ordinates, which are calculated by a simple procedure. The gradient and intercept of the segment in LNO co-ordinates are calculated assuming a straight line and using only the first and last points on the segment. The errors and covariance are also calculated but it is not know if these will be used in the online environment.
The TCVH bank is the ARAXNE-BOS bank for segments in LNO co-ordinates. This information must be further converted to the CTD global co-ordinates and put into the TCVC bank for the track finding stage. Following the offline approach, TCVH to TCVC is performed in SSREAD (see figure 3).