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RANSAC

RANSAC

Name


    RANSAC

Purpose


    RANSAC is an abbreviation for "RANdom SAmple Consensus". It is an
    iterative method to estimate parameters of a mathematical model
    from a set of observed data which contains outliers. It is a
    non-deterministic algorithm in the sense that it produces a
    reasonable result only with a certain probability, with this
    probability increasing as more iterations are allowed. The
    algorithm was first published by Fischler and Bolles in 1981.
    A basic assumption is that the data consists of "inliers", i.e.,
    data whose distribution can be explained by some set of model
    parameters, and "outliers" which are data that do not fit the
    model. In addition to this, the data can be subject to noise.
    The outliers can come, e.g., from extreme values of the noise
    or from erroneous measurements or incorrect hypotheses about the
    interpretation of data. RANSAC also assumes that, given a
    (usually small) set of inliers, there exists a procedure which
    can estimate the parameters of a model that optimally
    explains or fits this data (http://en.wikipedia.org/wiki/RANSAC).

Category


    Statistics.

Calling Sequence


    Result = $
      RANSAC( data, $
              fittingFunction, $
              distanceFunction, $
              minimumSamples, $
              distanceThreshold )

Inputs


    data
      Data set for which you are trying to determine a
      model. The data set is an array for which the
      number of columns corresponds to the number of
      dimensions in the data and the number of rows
      represents the number of observations [d,npts].
    fittingFunction
      A string representing the name of the fitting
      function to be used for the data. The calling
      sequence parameters must be ( data, status ) where
      a status of 1 represents a successful fit and a
      status of 0 indicates that some error occurred.
    distanceFunction
      A string representing the name of the distance
      function that determines the inlier points in the
      data set (data) that fall within a specified
      threshold distance (distanceThreshold) of the
      model defined by the fit parameters (modelParameters).
      This function returns the row indices of the
      provided data array that are inliers for the model.
    minimumSamples
      The minimum number of points that are required to
      fit the desired model.
    distanceThreshold
      The maximum distance a data point may be located
      from the determined model to still be considered
      an inlier.

Keyword Parameters


    MAXIMUM_TRIALS
      The maximum number of iteratons (default=1000).
    MAXIMUM_ATTEMPTS
      The maximum number of attempts that will be made
      to fit a non-degenrate model for a particular set
      of randomly selected points (default=100).
    PROBABILITY_ERROR_FREE_SELECTION
      The desired probability of choosing at least one
      sample free from outliers (default=0.99)
    INLIERS
      An optionally returned array containing the row indices
      corresponding to the rows of the provided data set
      that represent the best set of inliers chosen from the
      data set.
    VERBOSE
      If set, this routine will return diagnostic information.
    WIDGETID
      If set, this routine will return diagnostic information
      to the provided widget element ID using the SET_VALUE
      parameter and the WIDGET_CONTROL procedure.

Return Value


    Result is an array containing the parameters of the best fit model
    determined during the RANSAC process.

Side Effects


    None

Requires


    RANDOM_SAMPLE

Reference


    Fischler, Martin A. and Robert C. Bolles, Random sample consensus:
    A paradigm for model fitting with aplications to image analysis
    and automated cartography, Transactions of ACM - Graphics and
    Image Processing, Volume 24, Number 6, June 1981, pp. 381-395.

Modification History


    Written by: Carl Salvaggio
    September, 2008 Original code
    October, 2008 Modified to work with GUI by adding WIDGET parameter
   

Disclaimer


    This source code is provided "as is" and without warranties as to performance
    or merchantability. The author and/or distributors of this source code may
    have made statements about this source code. Any such statements do not
    constitute warranties and shall not be relied on by the user in deciding
    whether to use this source code.
    This source code is provided without any express or implied warranties
    whatsoever. Because of the diversity of conditions and hardware under which
    this source code may be used, no warranty of fitness for a particular purpose
    is offered. The user is advised to test the source code thoroughly before
    relying on it. The user must assume the entire risk of using the source code.



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