### view scripts/geometry/rectint.m @ 15489:481417a57a2d

improve sign and signbit docs * mappers.cc (Fsign): Note sign (-0) is 0. Add @seealso for signbit. (Fsignbit): Add @seealso for sign.
author John W. Eaton Thu, 04 Oct 2012 10:20:59 -0400 86854d032a37
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```
## Copyright (C) 2008-2012 Bill Denney
##
## This file is part of Octave.
##
## Octave is free software; you can redistribute it and/or modify it
## the Free Software Foundation; either version 3 of the License, or (at
## your option) any later version.
##
## Octave 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 Octave; see the file COPYING.  If not, see

## -*- texinfo -*-
## @deftypefn {Function File} {@var{area} =} rectint (@var{a}, @var{b})
##
## Compute the area of intersection of rectangles in @var{a} and
## rectangles in @var{b}.  Rectangles are defined as [x y width height]
## where x and y are the minimum values of the two orthogonal
## dimensions.
##
## If @var{a} or @var{b} are matrices, then the output, @var{area}, is a
## matrix where the i-th row corresponds to the i-th row of a and the j-th
## column corresponds to the j-th row of b.
##
## @seealso{polyarea}
## @end deftypefn

## Author: Bill Denney <bill@denney.ws>

function area = rectint (a, b)

if (nargin != 2)
print_usage ();
elseif (ndims (a) != 2 || ndims (b) != 2)
error ("rectint: expecting arguments to be 2-d arrays");
elseif (columns (a) != 4)
error ("rectint: A must have 4 columns");
elseif (columns (b) != 4)
error ("rectint: B must have 4 columns");
elseif (any ([a(:,3:4);b(:,3:4)](:) < 0))
error ("rectint: all widths and heights must be > 0");
endif

## This runs faster if the number of rows of a is greater than the
## number of rows of b.  Swap them and transpose to make it run
## faster.
swapinputs = false ();
if (rows (a) > rows (b))
tmp = a;
a = b;
b = tmp;
swapinputs = true ();
endif

area = zeros (rows (a), rows (b));
r1 = [a(:,1:2) a(:,1:2)+a(:,3:4)];
r2 = [b(:,1:2) b(:,1:2)+b(:,3:4)];
for i = 1:columns (area)
## Find the location of each point relative to the other points.
r1x1small = r1(:,1) < r2(i,1);
r1x1large = r1(:,1) > r2(i,3);
r1x1mid = (r1(:,1) >= r2(i,1)) & (r1(:,1) <= r2(i,3));
r1x2small = r1(:,3) < r2(i,1);
r1x2large = r1(:,3) > r2(i,3);
r1x2mid = (r1(:,3) >= r2(i,1)) & (r1(:,3) <= r2(i,3));

r1y1small = r1(:,2) < r2(i,2);
r1y1large = r1(:,2) > r2(i,4);
r1y1mid = (r1(:,2) >= r2(i,2)) & (r1(:,2) <= r2(i,4));
r1y2small = r1(:,4) < r2(i,2);
r1y2large = r1(:,4) > r2(i,4);
r1y2mid = (r1(:,4) >= r2(i,2)) & (r1(:,4) <= r2(i,4));

## determine the width of the rectangle
## r1 completely encloses r2
area(r1x1small & r1x2large,i) = r2(i,3) - r2(i,1);
## the range goes from r2x min to r1x max
## the range goes from r1x min to r2x max
## the range goes from r1x min to r1x max

## determine the height of the rectangle
## r1 completely encloses r2
area(r1y1small & r1y2large,i) .*= r2(i,4) - r2(i,2);
## the range goes from r2y min to r1y max
## the range goes from r1y min to r2y max
## the range goes from r1x min to r1x max

endfor

if (swapinputs)
area = area';
endif

endfunction

## Exactly overlapping
%!assert (rectint ([0 0 1 1], [0 0 1 1]), 1)
## rect2 completely enclosed by rect1
%!assert (rectint ([-1 -1 3 3], [0 0 1 1]), 1)
## rect1 completely enclosed by rect2
%!assert (rectint ([0 0 1 1], [-1 -1 3 3]), 1)
## rect1 right and top in rect2
%!assert (rectint ([-1 -1 1.5 1.5], [0 0 1 1]), 0.25)
## rect2 right and top in rect1
%!assert (rectint ([0 0 1 1], [-1 -1 1.5 1.5]), 0.25)
## no overlap - shared corner
%!assert (rectint ([0 0 1 1], [1 1 2 2]), 0)
## no overlap - shared edge
%!assert (rectint ([0 0 1 1], [0 1 2 2]), 0)
## Correct orientation of output
%!assert (rectint ([0 0 1 1;0.5 0.5 1 1;-1 -1 2 2], [1 1 2 2]), [0;0.25;0])
%!assert (rectint ([1 1 2 2], [0 0 1 1;0.5 0.5 1 1;-1 -1 2 2]), [0 0.25 0])

```