I have Centre of Pressure data for a standing horse in a horse trailer, from transducers in the floor. These data are collected at 1Hz, and the attached file shows the data. The data is in X (transverse) and Y (fore-aft) coordinates. The horse in this trial was standing at about 45deg to the long axis of the trailer, and so the excursion of the centre of pressure, as the horse swayed in response to movements of the trailer, is an oval shape, angled approximately at 45deg. I need to be able to express the movements, not in the trailer's X-Y directions, but in the transverse and fore-aft directions of the horse (transverse is medio-lateral, and fore-aft is cranio-caudal to the horse). So, I need to rotate the excursion pattern counter-clockwise by 45deg, or in some other way express the motions in the rotated X-Y dimensions. Any ideas?