urx.wave - moduleus/urx GitHub Wiki

Geometry of a transmitted wave or beam.

Parameter	Datatype	Description
parameters	Array of double	Geometric parameters of the wave. Interpretation of this array depends on the value of type. See notes.
time_zero	double	Time delay between the start of the transmit_setup and the moment this wave reaches the time_zero_reference_point, in [s]. Default NaN.
time_zero_reference_point	vector3d	Point in space that the wave passes through at time_zero. Expressed in the transmit_setup.probe coordinate system. See notes.
type	wave_type	Enumerated type describing the type of wave.

The wave.parameters field describes the geometric properties of the wave. The content of the array depends on the type of wave set in wave.type:

wave.type	wave.parameters	Description
CONVERGING_WAVE	$[x, y, z]$	3D Cartesian coordinates of wave's focal point.
CYLINDRICAL_WAVE	$[x, y, z, n_x, n_y, n_z]$	The cylindrical wave is parametrized by an axis $(n_x,n_y,n_z)$ and a point $(x, y, z)$, all expressed in 3D cartesian coordinates.
DIVERGING_WAVE	$[x, y, z]$	3D Cartesian coordinates of the wave's virtual source.
PLANE_WAVE	$[n_x, n_y, n_z]$	3D Cartesian coordinates of the direction vector of the plane. The vector must be unit-length: $\sqrt{n_x^2 + n_y^2 + n_z^2} = 1$.

The attributes parameters and wave_type describe the ultrasound wave is space. To locate the wave in the time-domain the attributes time_zero and time_zero_reference_point indicate the time (time_zero) at which the wave front crosses a specific point in space (time_zero_reference_point). The wave front is the plane of maximum of energy, usually the middle of the excitation pattern.

The following two diagrams show an example for a plane-wave, time_zero is referenced at the start of the transmit_setup: The plane-wave (in red) is defined by its direction's vector $\vec{n}$. At $t=t_{zero}$ the plane wave crosses the point $P_{ref}$.

Infinite combination of time_zero and time_zero_reference_point can describe the same wave. It is common but not mandatory to have one of the two attribute set to 0 or the origin. The following diagram represents the same plane-wave (in red) at different times. All the time_zero and time_zero_reference_points pairs: $(t_A, P_A)$, $(t_B, P_B)$, $(t_C, P_C)$, $(t_D, P_D)$ are equivalent, they locate in time the same wave.

excitation | transmit_setup | wave_type