FSC NEW - Fourier shell correlation and resolution determination ||

(04/5/16)

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

  1. 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)]

  2. 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.

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

SUBROUTINES

PR3D, PR3DB, FMRS_3

CALLER

FOUR1

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