Each instance of Vehicle has the following fields:

heading::Float64    # east of north (degrees)
max_step::Float64   # max distance vehicle can go per unit time (meters)

There are several constructors. Below is the default:

v = Vehicle(x::Real, y::Real, h::Real, ms::Real, s::Sensor)

If you just give it a starting location, heading is set to 0, max_step is set to 2.0, and the sensor is defaulted to BearingOnly(10.0) (a bearing-only sensor with noise std deviation of 10 deg).

v = Vehicle(x::Real, y::Real)

Alternatively, you can pass the sensor in as well, with the omitted variables as above:

v = Vehicle(x::Real, y::Real, s::Sensor)