Octave contourc format -> point coordinates

Question

octave saves the data of a contour in the contourc format which is a little bit special for me.

Is there some function or script which translates these data into a sequence of point coordinates which I can plot then? For one level only!

Thanks

Tasos Papastylianou Tasos Papastylianou · Accepted Answer · 2017-06-27T14:24:56

Example to process contourc format for one level (with potentially more than one contours at that level).

A = zeros(5); A(2:4,2:4) = 1; A(3,3) = 0; % example image
ContourCFormat = contourc(A, 1); % one level only (but here happens to have two contours)
C = cell();
while ~isempty(ContourCFormat)
  N = ContourCFormat(2,1);
  C{end+1} = ContourCFormat(:, 2 : 1+N); 
  ContourCFormat(:, 1 : 1+N) = []; % Remove processed points
end

C =
{
  [1,1] =

     1.5000   2.0000   3.0000   4.0000   4.5000   4.5000   4.5000   4.0000   3.0000   2.0000   1.5000   1.5000   1.5000
     2.0000   1.5000   1.5000   1.5000   2.0000   3.0000   4.0000   4.5000   4.5000   4.5000   4.0000   3.0000   2.0000

  [1,2] =

     2.5000   3.0000   3.5000   3.0000   2.5000
     3.0000   2.5000   3.0000   3.5000   3.0000

}

Explanation: From the octave manual:

The return value is a 2xn matrix containing the contour lines in the following format:
[lev1, x1, x2, …, levn, x1, x2, ...
 len1, y1, y2, …, lenn, y1, y2, …]
in which contour line n has a level (height) of levn and length of lenn.

Therefore for the first contour, we collect columns from 2 to N+1, where N is given by element (2,1) of the contourc output. Then we delete N+1 elements and process the next contour in the same way, until there are no more points left.

Octave contourc format -> point coordinates

1 Answers