**PURPOSE**- Calculates a 3D reconstruction by back-projecting the input projections using interpolation in Fourier space. See: Comparison of 'BP' operations. This operation is used to merge a number of independently created 'back projections' created by the 'BP 3F' operation. Example.

**SEE ALSO****BP 3F**[Back Projection - 3D, Interpolated in Fourier space ||*] **BP 3F PART**[Back Projection - 3D, Interpolated in Fourier space, Partial ||]

**USAGE**- .OPERATION: BP 3F

- .PARTIAL VOLUME FILES TEMPLATE: PROJ***

[Enter a template for back projected input volumes. This template can alternatively refer to a series of single volumes (e.g. bpvol***) or to a series of stacked volumes (e.g bpvolstk@***).] - If the template contains an asterisk SPIDER will ask:

.FILE NUMBERS OR SELECTION DOC. FILE NAME: IMAGE_SEL

[Enter volume file numbers or the name of the document file which contains the volume file numbers in its first register column.].SYMMETRIES DOC FILE: symmetries

[If there are no symmetries, enter symbol "*".

Otherwise, enter the name of the document file containing Eulerian angles defining symmetries (psi, theta, phi). The angles should be such that when used in operation 'RT 3D' transform the volume into itself. The identity operation (angles 0,0,0) MUST be included.

The symmetries are enforced in two steps: projections related by the symmetry operations are added in Fourier space to the volume; in order to reduce the residual artifacts, additional real-space symmetrization is applied.].RECONSTRUCTED VOLUME FILE: MERGED-VOL001

[Name for the merged output volume.]

**NOTES**

- 5x5x5 Kaiser-Bessel interpolation scheme is used.
- Operation NOT parallelized for use with MPI.
- Implemented by ArDean Leith.

**SUBROUTINES**- BP3F, SYMVOL, FILLBESSI0, FMRS

**CALLER**- VTIL2

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