polar coordinates
plural noun
1- Geometry a pair of coordinates locating the position of a point in a plane, the first being the length of the straight line (r) connecting the point to the origin, and the second the angle (θ) made by this line with a fixed line【几何】（平面）极坐标。
1.1
- the coordinates in a three-dimensional extension of this system（立体）极坐标。