TM series for X and Y(from P. D. Thomas)
and where is a small parameter of the ERM,
the series expansion for X is given by,
and where Sø is the arc length along the meridian through P from the
origin. Sø is given in a series and is a function of latitude (ø) only.
COM computations for TM and UTM involve inversion of this series
to get the footpoint latitude.