**PURPOSE**- Calculates the Fourier Shell Correlation (FSC) curve between two volumes. Stores the FSC curve in a doc file and reports the resolution at which FSC falls below cutoffs of 0.5 and 0.143. Can apply a mask from a file to volumes before the FSC calculation. Takes real input volumes only. This operation improves upon the previous 'FSC' operation. Example.

**SEE ALSO****FSC**[Fourier shell correlation and resolution determination ||] **RF 3**[Phase Residual & Fourier shell correlation, 3D ||] **FRC**[Fourier ring correlation and resolution determination ||] **MO 3**[Create Model volume]

**USAGE**- .OPERATION: FSC NEW [vg],[sfg],[resg], [v1],[sf1],[res1]

- [This operation can return up to six optional register variables:
Variable Example Receives First [vg] Interpolated voxel where the FSC falls below 0.143 Second [sfg] Resolution (in spatial frequency units) at this 'gold standard' level Third [resg] Resolution (in Angstroms) at this this 'gold standard' level First [v1] Interpolated voxel where the FSC falls below 0.5 Second [sf1] Resolution (in spatial frequency units) at 0.5 cuttoff Third [resl] Resolution (in Angstroms) at at 0.5 cuttoff If there are multiple downward crossings of the FSC cutoff line then the values are reported for the

**FIRST**crossing. If there is no such crossing the**minimum**from the FSC curve is used as a cuttoff location.].FIRST INPUT VOLUME: SUB001

[Enter name of first input volume. File must be real format.].SECOND INPUT VOLUME: SUB002

[Enter name of second input volume. File must be same size as first input file.].SHELL WIDTH (RECIPROCAL SPACE UNITS): 0.5

[Enter the shell width in**pixel/voxel**units.].VOXEL SIZE (A): 2.8

[Enter the voxel size in Angstroms. If unknown, enter 1.0 and resolution column will be reported in voxel units. ].INPUT MASK VOLUME (* IF NONE): mask001

[Enter name for file which contains the mask. File must be same size as input files. Enter '*' if you do not want any masking.].FSC OUTPUT DOCUMENT FILE: DOC001

[Enter name for the output document file containing the FSC curve.].GNUPLOT FILE: res-plot.gn

[Enter name for file which will contain Gnuplot commands which can plot the FSC curve. Enter '*' if you do not want a plotting file.]

**NOTES**

- The following measures are reported in the doc file for each shell :

a) Normalized Frequency. |NORM-FREQ| ---- Doc. file register: #1

a) Resolution in Angstroms. |Resolution| ---- Doc. file register: #2

c) Fourier Shell Correlation |FSC| ---- Doc. file register: #3

[SUM(F1 * CONJ(F2))] / [SQRT{SUM(ABS(F1)**2) * SUM(ABS(F2)**2)}]

where 'CONJ' denotes complex conjugate.

d) Square root of Fourier Shell Correlation |SQRT-FSC| ---- Doc. file register: #4

[SQRT(FSC)]

e) Square root (2 * Fourier Shell Correlation / (FSC + 1)) |SQRT-2FSC/(FSC+1)| ---- Doc. file register: #5

[SQRT(2*FSC/(FSC+1)] - References:

Saxton and Baumeister,*J. of Microscopy*, 127,(1982) 127-138.

M. van Heel,*Ultramicroscopy*, 21, (1987) 95-100.

Unser, et. al.,*Ultramicroscopy*, 23, (1987) 39-52.

- Pawel Penczek has notes on interpreting FRC/FSC curves.

**SUBROUTINES**- PR3D, PR3DB, FMRS_3

**CALLER**- FOUR1

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