Jasper Menger

super cool and useful. now to have it write an avi file...

Hi,
cutpolygon is a very helpful tool,
but I found one thing I do not understand.
If I cut a polygon by a vertical line, the intersection points
will not be computed correct. The value for the y-coordinate
will be taken from the first point which will be cut-out.

I modify your code at the following lines:
                elseif xx3 < xx1
% modified/add lines
% compute intersection point
                    X3(i) = xx1; xp = xx1;
                    yp = interp1([xx3, xx4], [yy3, yy4], xx1, 'linear', 'extrap');
                    Y3(i) = yp;
%r Original code
% X3(i) = xx1; xp = xx1; yp = yy3;
                elseif xx4 < xx1
% modified/add lines
% compute intersection point
                    X4(i) = xx1; xp = xx1;
                    yp = interp1([xx3, xx4], [yy3, yy4], xx1, 'linear', 'extrap');
                    Y4(i) = yp;
% Original code
% X4(i) = xx1; xp = xx1; yp = yy4;

and:
                elseif xx3 > xx1
% modified/add lines
% compute intersection point
                    xp = interp1([yy3, yy4], [xx3, xx4], yy1, 'linear', 'extrap');
                    X3(i) = xp; yp = yy3;
% Original code
% X3(i) = xx1; xp = xx1; yp = yy3;
                elseif xx4 > xx1
% modified/add lines
% compute intersection point
                    xp = interp1([yy3, yy4], [xx3, xx4], yy1, 'linear', 'extrap');
                    X4(i) = xp; yp = yy4;
% Original code
% X4(i) = xx1; xp = xx1; yp = yy4;

I hope that this would be a helpful comment for you.

The documentation and the help both suggest that xlogy(1,y) is defined as 1. This makes no sense, and it is also inconsistent with the code itself, since xlogy(1,y) actually returns 0 in this code.

Perhaps a better choice for xlogy(1,y) should be +/- inf., depending on the magnitude of y, with xlogy(1,1) == 0.