# HG changeset patch
# User Rik <rik@octave.org>
# Date 1580435036 28800
# Node ID 2e6dc7e2b191f84a5eddbbd64bcf192ca1125191
# Parent  262cdfc6faf915b8b3bd5c34c45c20760dace26a
Use appropriate Qhull options as necessary to obtain triangulation (bug #50494).

* __delaunayn__.cc (F__delaunayn__): Set default options for 2-D & 3-D input to
"Qt Qbb Qc" (no "Qz").

* delaunay.m: Document that default options for 2-D,3-D input are "Qt Qbb Qc".

* delaunayn.m: Document that default options for 2-D,3-D input are "Qt Qbb Qc".
Document that if triangulation fails, "Qz" will be added for 2-D inputs and
Qhull called a second time.  Add try/catch block that calls internal
function __delaunayn__ once with no options, and if an error results, calls
with "Qt Qbb Qc Qz" for 2-D inputs.

* griddata.m: Remove previous fix for bug #50494 which set Qhull options.

* griddatan.m: Remove previous fix for bug #50494 which set Qhull options.

diff -r 262cdfc6faf9 -r 2e6dc7e2b191 libinterp/dldfcn/__delaunayn__.cc
--- a/libinterp/dldfcn/__delaunayn__.cc	Thu Jan 30 15:12:52 2020 -0500
+++ b/libinterp/dldfcn/__delaunayn__.cc	Thu Jan 30 17:43:56 2020 -0800
@@ -133,7 +133,7 @@
   // Default options
   std::string options;
   if (dim <= 3)
-    options = "Qt Qbb Qc Qz";
+    options = "Qt Qbb Qc";
   else
     options = "Qt Qbb Qc Qx";
 
diff -r 262cdfc6faf9 -r 2e6dc7e2b191 scripts/geometry/delaunay.m
--- a/scripts/geometry/delaunay.m	Thu Jan 30 15:12:52 2020 -0500
+++ b/scripts/geometry/delaunay.m	Thu Jan 30 17:43:56 2020 -0800
@@ -55,7 +55,10 @@
 ## contains options passed to the underlying qhull command.
 ## See the documentation for the Qhull library for details
 ## @url{http://www.qhull.org/html/qh-quick.htm#options}.
-## The default options are @code{@{"Qt", "Qbb", "Qc", "Qz"@}}.
+## The default options are @code{@{"Qt", "Qbb", "Qc"@}}.
+## If QHull fails for 2-D input the triangulation is attempted again with
+## the options @code{@{"Qt", "Qbb", "Qc", "Qz"@}} which may result in
+## reduced accuracy.
 ##
 ## If @var{options} is not present or @code{[]} then the default arguments are
 ## used.  Otherwise, @var{options} replaces the default argument list.
diff -r 262cdfc6faf9 -r 2e6dc7e2b191 scripts/geometry/delaunayn.m
--- a/scripts/geometry/delaunayn.m	Thu Jan 30 15:12:52 2020 -0500
+++ b/scripts/geometry/delaunayn.m	Thu Jan 30 17:43:56 2020 -0800
@@ -45,11 +45,15 @@
 ## The default options depend on the dimension of the input:
 ##
 ## @itemize
-## @item 2-D and 3-D: @var{options} = @code{@{"Qt", "Qbb", "Qc", "Qz"@}}
+## @item 2-D and 3-D: @var{options} = @code{@{"Qt", "Qbb", "Qc"@}}
 ##
 ## @item 4-D and higher: @var{options} = @code{@{"Qt", "Qbb", "Qc", "Qx"@}}
 ## @end itemize
 ##
+## If QHull fails for 2-D input the triangulation is attempted again with
+## the options @code{@{"Qt", "Qbb", "Qc", "Qz"@}} which may result in
+## reduced accuracy.
+##
 ## If @var{options} is not present or @code{[]} then the default arguments are
 ## used.  Otherwise, @var{options} replaces the default argument list.
 ## To append user options to the defaults it is necessary to repeat the
@@ -64,7 +68,17 @@
     print_usage ();
   endif
 
-  T = __delaunayn__ (pts, varargin{:});
+  if (isempty (varargin) || isempty (varargin{1}))
+    try
+      T = __delaunayn__ (pts);
+    catch
+      if (columns (pts) <= 2)
+        T = __delaunayn__ (pts, "Qt Qbb Qc Qz");
+      endif
+    end_try_catch
+  else
+    T = __delaunayn__ (pts, varargin{:});
+  endif
 
   if (isa (pts, "single"))
     tol = 1e3 * eps ("single");
diff -r 262cdfc6faf9 -r 2e6dc7e2b191 scripts/geometry/griddata.m
--- a/scripts/geometry/griddata.m	Thu Jan 30 15:12:52 2020 -0500
+++ b/scripts/geometry/griddata.m	Thu Jan 30 17:43:56 2020 -0800
@@ -86,8 +86,7 @@
   z = z(:);
 
   ## Triangulate data.
-  ## Bug #50494 (loss of precision unless non-default Qhull options used)
-  tri = delaunay (x, y, {"Qt", "Qbb", "Qc"});
+  tri = delaunay (x, y);
   zi = NaN (size (xi));
 
   if (strcmp (method, "cubic"))
diff -r 262cdfc6faf9 -r 2e6dc7e2b191 scripts/geometry/griddatan.m
--- a/scripts/geometry/griddatan.m	Thu Jan 30 15:12:52 2020 -0500
+++ b/scripts/geometry/griddatan.m	Thu Jan 30 17:43:56 2020 -0800
@@ -60,11 +60,6 @@
     error ("griddatan: dimensional mismatch");
   endif
 
-  ## Bug #50494 (loss of precision unless non-default Qhull options used)
-  if (isempty (varargin) && n <= 3)
-    varargin{1} = {"Qt", "Qbb", "Qc"};
-  endif
-
   ## triangulate data
   tri = delaunayn (x, varargin{:});