[continues from 4.8]

4.9 Linearization coefficients

The position of a photon is computed by the Electronics Unit based on the output of the PMT. This process introduces a geometrical distortion because of three effects : The relevant distortion has been modelled using ground measurements with a multipinhole mask, and it is given as a third-order polynomial relation converting unlinearized x,y pixel positions into linearized X,Y positions in mm:

X = A3(1+A5/E) (x-A1) + A7 (x-A1) 2 + A9 (x-A1) 3

Y = A4(1+A6/E) (y-A2) + A8 (y-A2) 2 + A10 (y-A2) 3

In practice the above formula corresponds to a stepwise procedure in which :

The ten coefficients A1 to A10 are kept in files m{1,2,3}_xy.coeff


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