Question

Supose I have a matrix. This matrix is blank except some points that create rectangles with the same size. Every point that creates a rectangle has a positive number that is equal for all the points of that rectangle. It is posible that this matrix have several rectangles each with the same number.

Imagine now I have a second matrix with the same structure but now the rectangles are in other positions with an other size and an other values just as matrix A and B in the picture.

I want to combine both matrix so if there’s an intertection of some rectangle, the rectangle with the minimum number is erased.

Which is the best way to do it? I think that it can be posible doing fors but I want to do it 30 times so it will take a lot of time for Octave to complete it if I don’t improve it.

Answer 1

I have made this small code that seem to do the job:

A=[0 0 1 1 1 0 ;
   0 0 1 1 1 0 ;
   0 0 0 0 0 0 ;
   2 2 0 0 0 0 ;
   2 2 0 0 0 0 ;
   2 2 0 0 0 0 ];

B=[3 0 2 2 0 0 ;
   3 0 2 2 0 0 ;
   0 0 2 2 0 0 ;
   0 0 0 0 0 0 ;
   1 1 1 1 1 0 ;
   1 1 1 1 1 0 ];


%give a unique id to each rectangle
lblA=bwlabel(A);
lblB=bwlabel(B);

%search for overlap
overlap= A & B;

% find out overlaping rectangle s unique id
overlapLbl= unique([lblA(overlap(:)) lblB(overlap(:))],'rows');

%eliminate rectangle with lower score
for ov=1:size(overlapLbl,1)
  scoreA=A(find((lblA==overlapLbl(ov,1)),1));
  scoreB=B(find((lblB==overlapLbl(ov,2)),1));
  if scoreA>scoreB
    B(B==scoreB)=0;
  else
    A(A==scoreA)=0;
  end
end
C=A+B

output:

C =
     3     0     2     2     0     0
     3     0     2     2     0     0
     0     0     2     2     0     0
     2     2     0     0     0     0
     2     2     0     0     0     0
     2     2     0     0     0     0