Panel Zone

The Panel Zone consists of an array of region:-

• Region IDRG_PAN_ZONE, an irregular polygon. The serial number of the region is the number of the panel upon which it is centred.

Tracking into and through a panel zone, and the hexagons it contains, consists of the following steps:-

1. As a track leaves the H2O sphere the $\theta$ and $\phi$ of its exit point is computed and used in a fine grain look-up table to get the number of a nearby panel zone. The distance of the exit point to the centre of this panel is compared to the distance to all neighboring panels and if it is closer to any, the point is associated to the nearer panel and the test repeated. In this way the true panel zone is found by a stepwise search. The algorithm is efficient; almost half of the panel zones looked up are right and in almost all other cases one step is all that is required.

2. The lines is checked for intersection with the current panel and with all neighboring panels visible within the zone. This is dealt with in more detail below. Note: for a simple tesselating shape, sometimes neighboring panels intrude into the zone, indeed, this was one of the reasons why a simpler search strategy employed in SNOMAN up to version 2.05 had to be abandoned once the correct PMT arrangement was introduced. On average, a panel zone has 7 neighbours but only 3 are visible.

3. If there is no intersection before the line leaves the zone then the geometry returns the zone boundary.

4. When the geometry is called for a line that has reaches a zone boundary tracking proceeding the region that lies behind the boundary (one of the regions IDRG_PAN_ZONE, IDRG_H2O, or IDRG_OUT_DARK).

Tracking to and between hexagons within a single panel proceeds as follows:-

1. First, the enclosing polygon is used to veto tracks that don't come close to the panel.

2. The next step is to determine which hexagon is reached first. If hitting the front face, as most light will do, the code simply has to intersect the line with the front face and calculate the hexagon number; no searching is required. For lines that reach the side first, the line has to be intersected with all hexagon prisms through which it passes and is consequently a little slower.

3. Having found the panel hexagon, the region, which will be one of the regions IDRG_HEX_EMPTY, IDRG_PMT_OVL or IDRG_PMT_ABS, is determined.

4. When called for a line that has reaches a hexagon boundary tracking proceeds in the region that lies behind the boundary (either IDRG_PAN_ZONE, IDRG_HEX_EMPTY, IDRG_PMT_ABS or IDRG_PMT_OVL).

User Control

The user can select Mini-SNO panel configuration as described in section 12.2.6. Also it is possible to enable of diagnostic printout as described in 12.2.1. Currently it is not possible to pick points randomly in a Panel Zone.