Grid

A Grid is a set of equally spaced points in 1, 2 or 3 dimensions. Fields, phantoms and temperature maps in SonoSK are stored on one.

The last axis is always depth, measured away from the transducer:

Dimensions	Axes
1	(z)
2	(x, z)
3	(x, y, z)

import sonosk

g = sonosk.Grid((128, 128, 256), spacing=(0.1e-3, 0.1e-3, 0.05e-3))
g.ndim            # 3
g.extent          # length along each axis [m]
x, y, z = g.axes()
X, Y, Z = g.mesh()
pts = g.points()  # (N, 3) array of coordinates

Grid.centered puts the lateral axes symmetric about zero and starts the depth axis at a given value, which is the usual layout for a probe at the top of the image:

g = sonosk.Grid.centered((256, 512), 50e-6, depth_start=5e-3)

Sampling

points_per_wavelength(c, f) gives the number of grid points per wavelength for the slowest sound speed c at frequency f, using the coarsest spacing. The Rayleigh integral can be evaluated on any grid, so the spacing there only sets how finely the field is shown. The bioheat solver needs the heated region resolved by several points across, and the scatterer generator needs a spacing small against the resolution cell, since each scatterer takes the label of its nearest grid point.