Why do I receive an error message when using the GRIDDATA function in MATLAB 7.0 (R14)?

When I execute the command:

griddata([6 10 6 10], [25 25 125 125], [16 12 28 21], 8, 100)

I receive a very long error message that begins:

 ??? qhull precision error: initial facet 1 is coplanar with the interior point

 ERRONEOUS FACET:

 While executing:  | qhull d Qt Qbb Qc

 Options selected for Qhull 2002.1 2002/8/20:

   delaunay  Qtriangulate  Qbbound-last  Qcoplanar-keep  _pre-merge

   _zero-centrum  Pgood  Qinterior-keep  _max-width 1e+002

   Error-roundoff 1.7e-013  _one-merge 1.2e-012  Visible-distance 3.5e-013

   U-coplanar-distance 3.5e-013  Width-outside 6.9e-013  _wide-facet 2.1e-012

 precision problems (corrected unless 'Q0' or an error)

       2

flipped facets

 The input to qhull appears to be less than 3 dimensional, or a computation has overflowed.

 Qhull could not construct a clearly convex simplex from input points.

 The center point is coplanar with a facet, or a vertex is coplanar with a neighboring facet.  The maximum round off error for computing distances is 1.7e-013.

Answer 1

[MathWorks Support Team]

This enhancement has been incorporated in Release 2009b (R2009b). For previous product releases, read below for any possible workarounds:

This a result of the way that the GRIDDATA function in MATLAB interacts with the QHULL libraries to perform the calculations.

As a workaround, use the directions of the error message to interact directly with the QHULL routines. In this case, use the "QJ" option. You will need to specify the method that GRIDDATA uses (the default is 'linear'):

griddata([6 10 6 10], [25 25 125 125], [16 12 28 21], 8, 100, 'linear', {'QJ'})