Name

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  MGH_LOCATE2A

Purpose

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  This function calculates positions in the "index space" of a 2D
  curvilinear grid.

Calling Sequence

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  Result = MGH_LOCATE2(xin, yin)

Positional Parameters

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  xin, yin (input, 2-D numeric arrays)
    X & Y positions of the vertices of the curvilinear input grid.

Keyword Parameters

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  This function accepts the same keywords as GRIDDATA to define the
  output grid, ie: DELTA, DIMENSION, GRID, START, XOUT, YOUT.

Return Value

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  The function returns a floating array representing the output
  locations as fractional indices on the grid represented by the XIN
  & YIN arrays. The result is dimensioned [2,m] or [2,m,n] where [m]
  or [m,n] are the dimensions of the output locations.

Procedure

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  For each (x,y) pair in turn search for the location in 2D index space
  where the distance function d(x,y) = (xin-x)^2 + (yin-x)^2 is
  minimised.
  PERFORMANCE
  I have tested this function using a [439,439] moderately curved
  input grid (NZ region SST--see MGH_EXAMPLE_LOCATE2). Time taken is
  linear with number of output points @ 1050 per second on a Pentium
  4 2.67 GHz.
  See also MGH_LOCATE2 which has essentially the same functionality
  but is faster on larger output grids.
###########################################################################
  This software is provided subject to the following conditions:
  1. NIWA makes no representations or warranties regarding the
    accuracy of the software, the use to which the software may
    be put or the results to be obtained from the use of the
    software. Accordingly NIWA accepts no liability for any loss
    or damage (whether direct of indirect) incurred by any person
    through the use of or reliance on the software.
  2. NIWA is to be acknowledged as the original author of the
    software where the software is used or presented in any form.
###########################################################################

Modification History

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  Mark Hadfield, 2000-12:
    Written.