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MGH_BLOCKMEAN

MGH_BLOCKMEAN

Name


  MGH_BLOCKMEAN

Description


    Given (x,y,z) data--where x & y are vectors representing position
    on a 2D plane and z is a matching vector representing a scalar
    value at each position--and a 2D rectilinear or curvilinear grid,
    this function filters the input data and returns a reduced set of
    (x,y,z) values, where locations lying within the same grid cell
    have been combined into an average.
    This function is inspired by the GMT blockmean command:
      http://gmt.soest.hawaii.edu/gmt/doc/gmt/html/man/blockmean.html
    The grid is defined by a combination of the conventional DELTA,
    DIMENSION, START, XOUT and YOUT keywords (as used by GRIDDATA,
    except that the GRID keyword is omitted here because it can be
    inferred from the dimensionality of XOUT and YOUT). In the
    present case these define the positions of the cell vertices
    and the averaging is done over the cells, i.e we are using
    pixel node registration:
      http://gmt.soest.hawaii.edu/gmt/html/GMT_Docs.html#x1-188000B.2.2

Calling Sequence


    result = mgh_blockmean(x, y, z, w)

Positional Parameters


  x,y (input, numeric vector)
    Horizontal position of data.
  z (input, numeric vector)
    Horizontal position
  w (input, numeric vector, optional)
    Weights for weighted averaging

Keyword Parameters


    COUNT (output, integer scalar)
      Number of output values.
    DELTA (input, 1 or 2-element numeric vector)
      Grid spacing in the X & Y directions. This keyword, along with
      DIMENSION and START, can be used to define uniformly spaced
      rectilinear grids.
    DIMENSION (input, 1 or 2-element integer vector)
      Grid dimensions (number of vertices) in the X & Y
      directions. This keyword, along with DELTA and START, can be
      used to define uniformly spaced rectilinear grids.
    START (input, 1 or 2-element numeric vector)
      Grid origin in the X & Y directions. This keyword, along with
      DELTA and DIMENSION, can be used to define uniformly spaced
      rectilinear grids.
    XOUT, YOUT (input, 1-D or 2-D numeric arrays)
      Grid vertex positions, allowing grids with non-uniform spacing
      and curvilinear grids.

Return Value


    The function returns a [3,n] array containing the filtered
    (x,y,z) data. Note that the order of the original data will
    be lost.

Modification History


    Mark Hadfield, 2011-07:
      Written



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