Emilie asked on # angle clockwise or counterclockwise?

I am writing a program that needs to determine the angle between two line segments and whether the angle is clockwise or counterclockwise from the main segment.

How do I determine the direction of the angle from the main segment?

All the coordinates are positive numbers. The segments are of variant sizes.

The solution needs to be an equation since I will have to insert it in some code.

Thanks!

How do I determine the direction of the angle from the main segment?

All the coordinates are positive numbers. The segments are of variant sizes.

The solution needs to be an equation since I will have to insert it in some code.

Thanks!

Math / Science

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ask a questionEmilie

Math isn't exactly my forte. Would you mind explaining how to do a cross product of vectors?

Say I have a(x,y), b(x, y) and c(x, y), how do I do the cross product of ab x cb?

Say I have a(x,y), b(x, y) and c(x, y), how do I do the cross product of ab x cb?

Emilie

The cross product would be

(bx - ax)*(cy - ay) + (by - ay)*(cx - ax)

- x * y yields a positive number

- y * x yields a negative number

(bx - ax)*(cy - ay) + (by - ay)*(cx - ax)

- x * y yields a positive number

- y * x yields a negative number

This is the best money I have ever spent. I cannot not tell you how many times these folks have saved my bacon. I learn so much from the contributors.

rwheeler23

http://www.java2s.com/Open-Source/Java-Document/GIS/jts/com/vividsolutions/jts/algorithm/Angle.java.htm