The hit position in local coordinates is extracted with simple forms using projections of the pixel information; if desired, more sophisticated techniques should be easy to substitute.
In the direction perpendicular to the padrow and parallel to the padplane (i.e. ``radial''), the reconstructed hit is positioned at the center of the padrow. The two-dimensional pixel pattern gives no information regarding this direction.
The position along the padrow is determined using a 3-point Gaussian fit [3]:
where 
is the pad pitch, and 
and 
are the position and
the sum of ADC values on
the pad with the largest signal. 
and 
are sums on the
neighboring pads.
In the time direction, an offset weighted mean is used.
where 
is the ADC sum in time bucket i, projected onto the
time axis.
The STAR shaper amplifier (SAS) has response function [1]
to a TPC signal originating at time 
. The weighted mean of
this function, as well as the convolution of it with a time-symmetric
function (like Gaussian longitudinal diffusion), is offset from 
by
This holds even for non-zero crossing angles 
.
