CALICE conventions for indexing tracker hits

As for the calorimeters, the index of a tracker hit is meant to be the match maker between data and MC, therefore it encodes GEOMETRICAL informations. It is constructed from two independent values, the chamber position int dchPos and a flag int iXY to distinguish measurements of the x and y coordinates, respectively, according to
int index = 2*dchPos + iXY
Following conventions apply:

• iXY = 0 indicates the x-coordinate, iXY = 1 the y-coordinate
• dchPos is a number between 0 and 3 and counts backwards, i.e. dchPos = 3 is farthest from the calorimeters
• in case there are only 3 chambers present in the setup (as for CERN), the number range of dchPos is from 1 to 3

Note to developers: both MOKKA and TBTrack codes use the term 'layer' internally. Historically, MOKKA uses this to identify 'wire planes', i.e. the meaning is index in terms of the above definitions. Contrary to that, the TBTrack code refers to 'layer' as an identifier for the drift chamber, i.e. the dchPos variable in above notations.

-- NielsMeyer - 27 Nov 2008