--- a/INDEX
+++ b/INDEX
@@ -111,7 +111,8 @@
  entropyfilt
 Utilities
  getrangefromclass
- iptnum2ordinal
+ iptcheckconn
+ iptcheckmap
+ iptchecknargin
  iptcheckstrs
- iptchecknargin
- iptcheckmap
+ iptnum2ordinal

new file mode 100644
--- /dev/null
+++ b/inst/iptcheckconn.m
@@ -0,0 +1,78 @@
+## Copyright (C) 2011 Carnë Draug <carandraug+dev@gmail.com>
+##
+## This program is free software; you can redistribute it and/or modify
+## it under the terms of the GNU General Public License as published by
+## the Free Software Foundation; either version 3 of the License, or
+## (at your option) any later version.
+##
+## This program is distributed in the hope that it will be useful,
+## but WITHOUT ANY WARRANTY; without even the implied warranty of
+## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+## GNU General Public License for more details.
+##
+## You should have received a copy of the GNU General Public License
+## along with this program; if not, see <http://www.gnu.org/licenses/>.
+
+## -*- texinfo -*-
+## @deftypefn {Function File} {} iptcheckconn (@var{con}, @var{func_name}, @var{var_name}, @var{pos})
+## Check if argument is valid connectivity.
+##
+## If @var{con} is not a valid connectivity argument, gives a properly formatted
+## error message. @var{func_name} is the name of the function to be used on the
+## error message, @var{var_name} the name of the argument being checked (for the
+## error message), and @var{pos} the position of the argument in the input.
+##
+## A valid connectivity argument must be either double or logical. It must also
+## be either a scalar from set [1 4 6 8 18 26], or a symmetric matrix with all
+## dimensions of size 3, with only 0 or 1 as values, and 1 at its center.
+##
+## @end deftypefn
+
+function iptcheckconn (con, func_name, var_name, pos)
+
+  ## thanks to Oldak in ##matlab for checking the validity of connectivities
+  ## with more than 2D and the error messages
+
+  if (nargin != 4)
+    print_usage;
+  elseif (!ischar (func_name))
+    error ("Argument func_name must be a string");
+  elseif (!ischar (var_name))
+    error ("Argument var_name must be a string");
+  elseif (!isnumeric (pos) || !isscalar (pos) || !isreal (pos) || pos <= 0 || rem (pos, 1) != 0)
+    error ("Argument pos must be a real positive integer");
+  endif
+
+  base_msg = sprintf ("Function %s expected input number %d, %s, to be a valid connectivity specifier.\n       ", ...
+                      func_name, pos, var_name);
+
+  if (!any (strcmp (class (con), {'logical', 'double'})) || !isreal (con) || !isnumeric (con))
+    error ("%sConnectivity must be a real number of the logical or double class.", base_msg);
+  elseif (isscalar (con))
+    if (!any (con == [1 4 6 8 18 26]))
+      error ("%sIf connectivity is a scalar, must belong to the set [1 4 6 8 18 26].", base_msg);
+    endif
+  elseif (ismatrix (con))
+    center_index = ceil(numel(con)/2);
+    if (any (size (con) != 3))
+      error ("%sIf connectivity is a matrix, all dimensions must have size 3.", base_msg);
+    elseif (!all (con(:) == 1 | con(:) == 0))
+      error ("%sIf connectivity is a matrix, only 0 and 1 are valid.", base_msg);
+    elseif (con(center_index) != 1)
+      error ("%sIf connectivity is a matrix, central element must be 1.", base_msg);
+    elseif (!all (con(1:center_index-1) == con(end:-1:center_index+1)))
+      error ("%sIf connectivity is a matrix, it must be symmetric relative to its center.", base_msg);
+    endif
+  else
+    error ("%s", base_msg);
+  endif
+
+endfunction
+
+%!test ("iptcheckconn (4, 'func', 'var', 2)");                      # simple must work
+%!test ("iptcheckconn (ones(3,3,3,3), 'func', 'var', 2)");          # accept more than just 3D
+%!fail ("iptcheckconn (3, 'func', 'var', 2)");                      # does not belong to set
+%!fail ("iptcheckconn ([1 1 1; 1 0 1; 1 1 1], 'func', 'var', 2)");  # matrix center must be 1
+%!fail ("iptcheckconn ([1 2 1; 1 1 1; 1 1 1], 'func', 'var', 2)");  # matrix must be 1 and 0 only
+%!fail ("iptcheckconn ([0 1 1; 1 1 1; 1 1 1], 'func', 'var', 2)");  # matrix must be symmetric
+%!fail ("iptcheckconn (ones(3,3,3,4), 'func', 'var', 2)");          # matrix must have all sizes 3