Hi, From: https://www.euclideanspace.com/threed/games/examples/cars/collisions/index.htm "To rotate the vector through 90 degrees we just swap the x and y coordinates." This is untrue: (x, y) = (1, 1) (y, x) = (1, 1) Clearly not rotated 90 degrees. Swapping the x and y coordinates mirrors in the x-y plane, and so will seem to swap the coordinates if they lie on either axis. By 90 degrees are actually obtained by premultiplying the vector by the matrix: [0, 1 -1, 0] for anti-clockwise rotations and: [0, -1 1, 0] for clockwise rotations. In the article it doesn't matter if you rotate clockwise or anti-clockwise, so you could just say you swap the x and y coordinates, and make one negative. So: (x, y) = (1, 1) (-y, x) = (-1, 1) # 90 degrees clockwise (y, -x) = (1, -1) # 90 degrees anti-clockwise The example spreadsheet is also wrong with the same error. |