--- a/scripts/geometry/griddata3.m	Mon Apr 13 18:07:28 2020 -0700
+++ b/scripts/geometry/griddata3.m	Mon Apr 13 18:10:45 2020 -0700
@@ -28,18 +28,34 @@
 ## @deftypefnx {} {@var{vi} =} griddata3 (@var{x}, @var{y}, @var{z}, @var{v}, @var{xi}, @var{yi}, @var{zi}, @var{method})
 ## @deftypefnx {} {@var{vi} =} griddata3 (@var{x}, @var{y}, @var{z}, @var{v}, @var{xi}, @var{yi}, @var{zi}, @var{method}, @var{options})
 ##
-## Generate a regular mesh from irregular data using interpolation.
+## Interpolate irregular 3-D source data at specified points.
 ##
-## The function is defined by @code{@var{v} = f (@var{x}, @var{y}, @var{z})}.
+## The inputs @var{x}, @var{y}, and @var{z} define the points where the
+## function @code{@var{v} = f (@var{x}, @var{y}, @var{z})} is evaluated.  The
+## inputs @var{x}, @var{y}, @var{z} are either vectors of the same length, or
+## if they are of unequal length, then they are expanded to a 3-D grid with
+## @code{meshgrid}.  The size of the input @var{v} must match the size of the
+## original data, either as a vector or a matrix.
+##
 ## The interpolation points are specified by @var{xi}, @var{yi}, @var{zi}.
 ##
-## The interpolation method can be @qcode{"nearest"} or @qcode{"linear"}.
-## If method is omitted it defaults to @qcode{"linear"}.
+## The optional input interpolation @var{method} can be @qcode{"nearest"} or
+## @qcode{"linear"}.  When the method is @qcode{"nearest"}, the output @var{vi}
+## will be the closest point in the original data (@var{x}, @var{y}, @var{z})
+## to the query point (@var{xi}, @var{yi}, @var{zi}).  When the method is
+## @qcode{"linear"}, the output @var{vi} will be a linear interpolation between
+## the two closest points in the original source data in each dimension.
+## If @var{method} is omitted or empty, it defaults to @qcode{"linear"}.
 ##
 ## The optional argument @var{options} is passed directly to Qhull when
 ## computing the Delaunay triangulation used for interpolation.  See
 ## @code{delaunayn} for information on the defaults and how to pass different
 ## values.
+##
+## Programming Notes: If the input is complex the real and imaginary parts
+## are interpolated separately.  Interpolation is based on a Delaunay
+## triangulation and any query values outside the convex hull of the input
+## points will return @code{NaN}.
 ## @seealso{griddata, griddatan, delaunayn}
 ## @end deftypefn
 
@@ -105,3 +121,7 @@
 %! vi = griddata3 (x, y, z, v, xi, yi, zi, "nearest");
 %! vv = vi - xi.^2 - yi.^2 - zi.^2;
 %! assert (max (abs (vv(:))), 0.385, 0.1);
+
+## FIXME: Ideally, there should be BIST tests for input validation.
+## However, this function is deprecated in Matlab and it probably isn't worth
+## the coding time to work on a function that will be removed soon.