Overview of the Design

SNOMAN has 2 Geometry Software Units:-

GEO

A general geometry describing every element of the detector except for the PMTs. This geometry is designed to be flexible; adding new element is relatively simple.

PMT

Is a tracking package within a PMT and has its own geometry dedicated to the PMT internal structure. This is a hardwired geometry designed for optimum performance.

In this chapter GEO, the general detector geometry, is described; the PMT simulation has a chapter of its own.

The design of the geometry can be summarised as follows:-

• It is not data driven (too slow); each region is hardwired.

• An attempt is made to use object orientated approach (as far as FORTRAN allows!) Each region is an object that knows only about its own boundaries and that it can ``see'' other regions - either internally or externally and calls them to deal with their boundaries.

• The ownership of boundaries and overlapping regions are assigned on the basis of priority.

• The software is organised into 4 tiers:-
  • Interface
  • Detector Elements i.e. the objects.
  • Primitives from which detector elements are built.
  • Boundary manager that processes primitive boundaries.

• The software deals with 4 types of request:-

  NEXT

  Find the distance to the next boundary in given direction.

  NEAR

  Find the distance to the nearest boundary in any direction.

  PICK

  Pick a point in region randomly.

  REGION

  Find region for given point.