openlifu.geo.create_standoff_transform

openlifu.geo.create_standoff_transform(z_offset: float, dzdy: float) → ndarray

Create a standoff transform based on a z_offset and a dzdy value.

A “standoff transform” applies a displacement in transducer space that moves a transducer to where it would be situated with the standoff in place. The idea is that if you start with a transform that places a transducer directly against skin, then pre-composing that transform by a “standoff transform” serves to nudge the transducer such that there is space for the standoff to be between it and the skin.

This function assumes that the standoff is laterally symmetric, has some thickness, and can raise the bottom of the transducer a bit more than the top. The z_offset is the thickness in the middle of the standoff, while the dzdy is the elevational slope.

Parameters:

• z_offset – Thickness in the middle of the standoff

• dzdy – Slope of the standoff, as axial displacement per unit elevational displacement. A positive number here means that the bottom of the transducer is raised a little bit more than the top.

Returns a 4x4 matrix representing a rigid transform in whatever units z_offset was provided in.