[EDIT: 20110629 12:13 CDT - reformat - WDR]
What I am trying is to find area of a polygon i.e. ractangle using conic sectors. For this I create a conic mask (extracted from a circle) and then rotate it over the rectangle. Let say center of the rectangle is (x, y) = [76.6, 44.1], then I would create a meshgrid with the center [cx cy] = [76.6, 44.1] and then find the conic mask with this base/origan. I have managed to make a conic mask at say [76.6, 44.1] but unfortunatly it is not the center of the mesh. So when I rotate the meshgrid using imrotate, the conic mask loses its center/base. Consequently after first iteration of theta, I am not able to caclulate the area of rectangle for the rest of conic sections. SOLUTION is that if I am able to draw cx and cy as the center of the meshgrid, then by simply imrotate my mask will rotate and I will get the area of the rectangle by rotating the mask all around 360'.
My code is as follows for creating the mask:
r = 40;
cx = 76.6;
cy = 44.1;
Theta = 30;
Theta1 = Theta / 2;
ix = 3*r; iy = 3*r;
[X, Y] = meshgrid(-(cx - 1):(ix - cx), -(cy - 1): (iy - cy));
c_mask = ((X.^2 + Y.^2) <= r^2);
Slope = tand(Theta1);
l1 = Y - Slope * X;
L1 = (l1 < 0.0);
Slope = tand(-Theta1);
l2 = Y - Slope * X;
L2 = (l2 > 0.0);
Sector = immultiply(L1,L2);
c_mask = immultiply(Sector, c_mask);
figure ,
subplot(311), imshow(L1), title('Line 1')
axis on, hold on
subplot(312), imshow(L2), title('Line 2')
axis on, hold on
subplot(313), imshow(Sector), title('Conic sector')
axis on, hold on
h = imcontour( Sector, 1, 'r');
