cutting_crew

08-28-2008, 02:34 PM

i have a polygon with a set of known vertices but i keep getting negative numbers for my areas. i was wondering what i am doing wrong?

i looked up the formula here. (http://en.wikipedia.org/wiki/Polygon) where it talks about in the middle about getting the area and the centroid and in this case i want to find A.

the point A is what i want to find. the first set of points happens to be:

-89.409 30.306

-89.409 30.308

-89.408 30.305

-89.407 30.304

-89.409 30.306

as you can see by the points this polygon going clockwise, therefore it is possible to get a negative number(this is referred to in the wiki article) but i wanted to be sure that i got the correct answer and am doing this correctly.

area = (-89.409 * 30.308 + -89.409 * 30.305 + -89.408 * 30.304 + -89*407 * 30.306) - (30.306 * -89.409 + 30.308 * -89.408 + 30.305 * -89.407 + 30.304 * -89.409)

area = area / 2;

answer = -0.2. can anyone confirm? and then thus taking the absolute value would give a final answer of 0.2. thanks all for the help!

i looked up the formula here. (http://en.wikipedia.org/wiki/Polygon) where it talks about in the middle about getting the area and the centroid and in this case i want to find A.

the point A is what i want to find. the first set of points happens to be:

-89.409 30.306

-89.409 30.308

-89.408 30.305

-89.407 30.304

-89.409 30.306

as you can see by the points this polygon going clockwise, therefore it is possible to get a negative number(this is referred to in the wiki article) but i wanted to be sure that i got the correct answer and am doing this correctly.

area = (-89.409 * 30.308 + -89.409 * 30.305 + -89.408 * 30.304 + -89*407 * 30.306) - (30.306 * -89.409 + 30.308 * -89.408 + 30.305 * -89.407 + 30.304 * -89.409)

area = area / 2;

answer = -0.2. can anyone confirm? and then thus taking the absolute value would give a final answer of 0.2. thanks all for the help!