restrictalign(1)            General Commands Manual           restrictalign(1)



NAME
       restrictalign - Restrict tilt alignment parameters for low number of
       fiducials

SYNOPSIS
       restrictalign  options  tiltalign_command_file

DESCRIPTION
       Restrictalign will modify the parameter settings in a command file for
       running Tiltalign so that they are appropriate for the number of
       fiducials available.  It uses two fundamentally different methods for
       reducing the number of variables being solved for.  The original
       method, currently the default, is based on the ratio of measured values
       to unknown variables.  Variables are reduced until this ratio rises to
       a target or minimum level.  Although this ratio provides some guidance
       for how to avoid over-fitting, this method cannot take into account the
       signal-to-noise ratio of the data, namely how much random error there
       is in the measurements.

   Cross-validation
       The newer method is cross-validation: running Tiltalign numerous
       times with a small fraction of points left out, measuring how well each
       solution predicts the positions of the points left out, and computing
       an average "leave-out error". This error, not the mean residual error,
       accurately reflects whether a different selection of parameters gives a
       better solution or not.  The mean residual will always go down when
       more variables are solved for (e.g, by adding a parameter to solve for
       or reducing its grouping), whereas the leave-out error will go down
       when the added variables improve the fit and go up when they over-fit
       to the data.  The downside of this superior method of avoiding overfit-
       ting is that it takes much more time for the many runs of Tiltalign;
       this becomes a major consideration with local alignments and many fidu-
       cials.

       The variables tested are completely different depending on whether
       local alignments are to be tested.  Without local alignments, the pro-
       gram tests a sequence of the global variables being solved for.  For
       each variable, it tests with default grouping if there is no grouping,
       with intermediate grouping, with very large grouping, and with the
       variable fixed (or, for rotation, with solving for only one rotation
       angle), stopping when the leave-out error rises.  The order of the
       tests is X-stretch and skew together, tilt angle, rotation, magnifica-
       tion, beam tilt, X axis tilt, and projection stetch.  With local align-
       ments, the program can test either by restricting alignment variables
       in a similiar sequence, or by increasing the size of local areas
       together with the required number of fiducials in each, or with both
       kinds of tests.  Here the sequence of variables is X-stretch and skew
       together, tilt angle, rotation, and magnification.  It is recommended
       that the area requirements be tested first because the same requirement
       tends to be chosen regardless of which order they are done in, whereas
       the variables tend to be restricted more when tested before the area
       requirement has been increased.

       If robust fitting is being done, the program may first disable it per-
       manently if the ratio of measurements to unknowns is too low.  If not,
       the program uses a weighted leave-out error computed with and without
       robust fitting to assess the benefit from robust fitting, and if the
       benefit is not above a criterion, it turns off robust fitting temporar-
       ily for all further tests simply in order to save time.

   Restrictions Based on the Ratio of Measurements to Unknowns
       In the old method, the program proceeds by applying a series of
       restrictions - grouping a variable instead of solving at every tilt, or
       fixing it instead of grouping - in a specified order until an appropri-
       ate ratio of measured values to unknown variables is reached.  That
       ratio is picked based on two parameters, the minimum required ratio,
       and a target ratio.  When two restrictions both give more than the min-
       imum ratio, the one closest to the target is chosen.  To have the pro-
       gram always pick the first restriction where the ratio is above the
       minimum, set the target ratio equal to the minimum ratio.

       The -order option controls the order in which restrictions will be
       applied by changes in the magnification, rotation, and tilt solutions,
       but these are not the only changes that can occur.  Before applying any
       of these restrictions, the stretching solution (X-stretch and skew),
       local alignments, and variable X-axis tilt (except between two halves
       of a tilt series) will be turned off.  If these restrictions are suffi-
       cient, no further changes are made.  When there are fewer than 4 beads,
       the beam tilt solution, projection stretch, and variable X-axis tilt
       between two halves of a tilt series are turned off; all of these
       involve solving for a single variable.  The solution for one rotation
       angle is turned off with only one bead.  When the ratio of measurements
       to unknowns falls below the minimum, robust fitting is turned off.

       The program always changes parameters so as to solve for fewer vari-
       ables than in the current file.  If the ratio is already greater than
       the minimum and closer to the target than with any restriction applied,
       no change will be made.

       To use the program with the default settings with a single-axis tilt
       series, simply enter:
          restrictalign align.com
       to use the original method, or
          restrictalign -cross 1 align.com
       to do cross-validation when local alignments are not being used, or
       restrictalign -cross 1 -local 3 align.com
       to test the local area requirements then the local variables.  The
       existing file will be renamed to align.com~ and the file with the
       changed parameters will be written as align.com, unless the -trial
       option is entered.

OPTIONS
       Restrictalign uses the PIP package for input (see the manual page for
       pip).  Options can be specified either as command line arguments
       (with the -) or one per line in a command file (without the -).
       Options can be abbreviated to unique letters; the currently valid
       abbreviations for short names are shown in parentheses.

       -align (-a) OR -AlignCommandFile    File name
              Command file for running Tiltalign. If this option is not
              entered, the first non-option argument will be used for the name
              of the command file.

       -fiducials (-f) OR -NumberOfFiducials    Integer
              Numbers of fiducial markers (beads) in the alignment model.
              With this entry, he program will assume that each bead is marked
              on every view.  If this option is not entered, the program will
              use the number of contours in the fiducial model with more than
              one point, and count up the number of points in those contours.
              The latter will give more accurate estimates of the ratio of
              measurements to unknowns when there beads marked on only a sub-
              set of views.

       -views (-vi) OR -NumberOfViews      Integer
              Number of views in the tilt series.  If this option is not
              entered, the program will use the number of views in the image
              file listed in the command file.

       -target (-ta) OR -TargetMeasurementRatio      Floating point
              Target ratio of measurements to unknown values.  If two succes-
              sive restrictions give a ratio above the minimum required by the
              -minimum option, the restriction that gives a ratio closest to
              this value will be chosen.  The default is 3.6.

       -minimum (-m) OR -MinMeasurementRatio    Floating point
              Minimum ratio of measurements to unknown values.  Restrictions
              will be applied until at least one ratio rises above this value.
              The default is 3.2.

       -cross (-c) OR -UseCrossValidation       Integer
              With this option, the program will test for the value of
              restricting the alignment parameters using cross-validation.
              Namely, alignment is run repeatedly with ~10% of points left
              out, and the error in predicting the positions of the left-out
              points from the solution obtained with the remaining points is
              computed.  A set of alignment parameters is considered to be
              better if it reduces this error, regardless of the effect on the
              mean residual of the fit with all points.  If 1 is entered, sets
              of 5 points on adjacent views are left out, with error measured
              from the middle 3 points.  If 2 is entered, contours will be
              left out instead.  The latter approach is unsuitable if there
              are few contours.

       -local (-l) OR -LocalAlignValidation     Integer
              Do cross-validation on local alignment parameters: enter 1 to
              test the variable selections, increasing the grouping or turning
              off magnification, rotation, tilt, and x-stretch and skew
              together.  Enter 2 to test the required number of fiducials in
              local areas while increasing their target size (or reducing the
              number if that is specified instead of target size).  Enter 3 or
              4 to do both tests, first areas then variables with a 3, or
              variables then areas with a 4.  These tests can take several to
              many minutes.  No tests will be done on global variable selec-
              tions.  Local alignment must be selected in the command file.

       -benefit (-b) OR -MinRobustBenefit       Floating point
              Minimum percentage benefit (reduction in leave-out error) with
              robust fitting needed to keep using robust fitting during cross-
              validation tests.  The benefit is the difference between the
              non-robust and robust weighted errors of the points left out,
              i.e., the weights from robust fitting with no points left out
              are applied identically to the prediction errors of the points
              left out without and with robust fitting.  When the benefit is
              less than the give amount, robust fitting will be omitted in
              order to speed up the tests.  The default is 2%.

       -order (-o) OR -OrderOfRestrictions      Multiple integers
              Order in which possible restrictions should be applied to
              achieve the target.  The restrictions are numbered as follows:
                1: Group rotations
                2: Solve for one rotation
                3: Fix tilt angles
                4: Group magnifications
                5: Fix magnifications
              The default order is  1,4,3,2,5, which means rotations will be
              grouped, then magnifications grouped, tilt angles fixed, then
              one rotation solved for, then magnifications fixed.

       -skipbeam (-s) OR -SkipBeamTiltWithOneRot
              By default, the program will add a solution for beam tilt if and
              when it switches to solving for only one rotation angle.  (If
              parameters are already set to solve for only one rotation angle,
              this switch does not occur and it will not add beam tilt.)  With
              this option, it will not add the beam tilt solution along with
              this restriction.

       -trial (-tr) OR -TrialMode
              Output modifications to a different command file instead of
              replacing the input file.  The output file will be named as the
              root of the input file plus "_new.com"

       -verbose (-ve) OR -VerboseOutput
              Output the errors at each step when doing cross-validation

       -PID   Print process ID

       -help (-h) OR -usage
              Print help output

       -StandardInput
              Read parameter entries from standard input


FILES
       The input file is renamed by adding a ~ to the end of its name and
       replaced with the new file, or new file is produced in trial mode with
       the root of the input name followed by "_new.com".

AUTHOR
       David Mastronarde

SEE ALSO
       tiltalign

BUGS
       Email bug reports to mast at colorado dot edu.



IMOD                                4.12.35                   restrictalign(1)