3D Projectors

Projectors define the parameters of the forward and backward projection operations. In 3D algorithms, only “cuda3d” (accelerated linear/Joseph/slice-interpolated) projector type is supported.

Creation

id = astra.create_projector("cuda3d", proj_geom, vol_geom)

id = astra_create_projector("cuda3d", proj_geom, vol_geom);

This script is a wrapper around the create method with a more convenient interface.

The allocated object can be freed after use with a call to:

astra.projector3d.delete(id)

astra_mex_projector3d('delete', id)

Configuration options

3D projectors support a ProjectionKernel option field in the config passed to the create method. The options are:

default : Standard forward/backprojection.
2d_weighting : Use backprojection weighting optimized for 2D slices. This makes backprojection closer to the true adjoint of the forward projection when the number of slices is small, whereas the default weighting works better for large numbers of slices.
matched_bp : In the backprojection, use the kernel producing the exact adjoint of the forward projection; slower and only available for ‘cyl_cone_vec’ geometry at the moment.

Additional options that can by specified in the options field in the config passed to the create method, or as options argument to the create_projector function:

Name	Description
VoxelSuperSampling	Each voxel in the volume will be subdivided by this factor along each dimension. This should only be used if voxels in the volume are larger than the detector pixels (default: 1).
DetectorSuperSampling	Each detector pixel in the projection will be subdivided by this factor along each dimension. This should only be used if detector pixels are larger than the voxels in the volume (default: 1).
GPUIndex	The index of the GPU to use (default: 0).

Note

Note that these options have lower priority than the options you can define when configuring the algorithms.

API

create

cfg = {
    "type": "cuda3d",
    "ProjectionGeometry": proj_geom,
    "VolumeGeometry": vol_geom
}
id = astra.projector3d.create(cfg)

cfg.type = 'cuda3d';
cfg.ProjectionGeometry = proj_geom;
cfg.VolumeGeometry = vol_geom;
id = astra_mex_projector3d('create', cfg);

Create a projector from a config object. This is called internally by create_projector, which is the recommended way to create projectors.

direct_FP / direct_BP

astra.projector3d.direct_FP(projector_id, volume_array, out=projection_array)
astra.projector3d.direct_BP(projector_id, projection_array, out=volume_array)

Perform a forward/backprojection of the given array and write the result to another array. Unlike the forward projection algorithm, this function does not require separate data and algorithm objects to be created within ASTRA. Instead, it accepts any CPU/CUDA arrays supporting DLPack standard (NumPy, PyTorch, JAX, etc.)

Note

Output projection/volume array can only be passed as an out keyword argument to avoid ambiguity.

volume_geometry

vol_geom = astra.projector3d.volume_geometry(id)

vol_geom = astra_mex_projector3d('volume_geometry', id);

Get the volume geometry attached to the given projector object.

Note

The returned geometry may slightly deviate from the original geometry because of internal data type conversions.

projection_geometry

proj_geom = astra.projector3d.projection_geometry(id)

proj_geom = astra_mex_projector3d('projection_geometry', id);

Get the projection geometry attached to the given projector object.

Note

The returned geometry may slightly deviate from the original geometry because of internal data type conversions.

delete

astra.projector3d.delete(id)
astra.projector3d.delete([id1, id2, ...])

astra_mex_projector3d('delete', id)
astra_mex_projector3d('delete', id1, id2, ...)

Free a single or multiple projector(s).

clear

astra.projector3d.clear()

astra_mex_projector3d('clear')

Free all projectors.

info

astra.projector3d.info()

astra_mex_projector3d('info')

Print basic information about all allocated projector objects.