area is now positive + for polygons drawn clockwise CW and negative - for polygons drawn counter-clockwise CCW Click Space to clear I have changed some features to improve them, including a glitch where it calculates twice the area instead and allowing to create polygons instead of curves. click "draw" then click mouse at places to put a point there. it must end up being at the beginning again. try drawing curves that do and do not contain the center, and which wrap around the center either CW or CCW. the list 'curve' lists the x coordinate and then the y coordinate for each point, and lists the first point both first and last. this uses a formula for the area of a triangle where for triangle given by two sides b and c and the included angle A, the area is equal to 1/2 * b*c * sin A, which I noticed is like the cross product of a vector b and vector c. in this case you have sines of negative angles so you have negative area when the triangle curves CCW viewed from the center. the cross product (modified for CW -> + ) is also ( y1*x2 - x1*y2 ) /2 . It just so happens that it works out, if you work it out for any shape.
