step calculation functions

calc_dx(x)

calc_dy(x)

calc_difftime(x)

calc_steplen(x)

calc_absangle(x, ..., dx, dy, len)

calc_speed(..., x, len, dt)

calc_relangle(..., x, abs_angle)

Arguments

x	an sftrack/sftraj object or in some cases a geometry
...	ignored
dx	(optional) output of calc_dx if already calculated. Otherwise will call `calc_dx()` internally
dy	(optional) output of calc_dy if already calculated. Otherwise will call `calc_dy()` internally
len	(optional) output of calc_steplen if already calculated. Otherwise will call `calc_steplen()` internally
dt	(optional) output of calc_difftime if already calculated. Otherwise will call `calc_difftime()` internally
abs_angle	(optional) output of calc_absangle if already calculated. Otherwise will call `calc_absangle()` internally