Editable parallel beam template

The following can serve as a template to construct a flexible parallel beam geometry. For a step by step walk through about modeling geometries in the lab frame, see Lab frame: rotating object instead of rotating detector.

import tomosipo as ts
import numpy as np

# Detector parameters:
pixel_size = 1.0
detector_shape=(10, 10)
detector_position = (0, 2, 0)

# Volume parameters:
volume_shape = np.array([1, 1, 1])
voxel_size = np.array([1.0, 1.0, 1.0])

# Rotation parameters
num_angles = 10
angles = np.linspace(0, np.pi, num_angles, endpoint=False)
rot_axis_pos = (0, 0.1, 0.2)

# Geometries
pg = ts.parallel_vec(
    shape=detector_shape,
    ray_dir=(0, 1, 0),
    det_pos=detector_position,
    det_v=(pixel_size, 0, 0),
    det_u=(0, 0, pixel_size),
)

vg0 = ts.volume(
    shape=volume_shape,
    pos=(0, 0, 0),
    size=volume_shape * voxel_size,
)
R = ts.rotate(pos=rot_axis_pos, axis=(1, 0, 0), angles=angles)
vg = R * vg0.to_vec()

A = ts.operator(vg, pg)