fix bug (#1702)

mmcv/ops/csrc/common/cuda/min_area_polygons_cuda.cuh

@@ -86,8 +86,8 @@ __device__ inline void minBoundingRect(Point *ps, int n_points, float *minbox) {
     float R[2][2];
     float rot_points[2][MAXN];
     R[0][0] = cos(unique_angles[i]);
-    R[0][1] = -sin(unique_angles[i]);
-    R[1][0] = sin(unique_angles[i]);
+    R[0][1] = sin(unique_angles[i]);
+    R[1][0] = -sin(unique_angles[i]);
     R[1][1] = cos(unique_angles[i]);
     // R x Points
     for (int m = 0; m < 2; m++) {
@@ -273,8 +273,8 @@ __device__ inline void Findminbox(T const *const p, T *minpoints) {
   float R[2][2];
 
   R[0][0] = cos(angle);
-  R[0][1] = -sin(angle);
-  R[1][0] = sin(angle);
+  R[0][1] = sin(angle);
+  R[1][0] = -sin(angle);
   R[1][1] = cos(angle);
 
   minpoints[0] = xmax * R[0][0] + ymin * R[1][0];

tests/test_ops/test_min_area_polygons.py

@@ -9,13 +9,13 @@ np_pointsets = np.asarray([[
     2.0, 1.5, 1.5
 ],
                            [
-                               1.5, 1.5, 2.5, 2.5, 1.5, 2.5, 2.5, 1.5, 1.5,
-                               3.5, 3.5, 1.5, 2.5, 3.5, 3.5, 2.5, 2.0, 2.0
+                               1.0, 1.0, 8.0, 8.0, 1.0, 2.0, 2.0, 1.0, 1.0,
+                               3.0, 3.0, 1.0, 2.0, 3.0, 3.0, 2.0, 1.5, 1.5
                            ]])
 
 expected_polygons = np.asarray(
     [[3.0000, 1.0000, 1.0000, 1.0000, 1.0000, 3.0000, 3.0000, 3.0000],
-     [3.5000, 1.5000, 1.5000, 1.5000, 1.5000, 3.5000, 3.5000, 3.5000]])
+     [8.0, 8.0, 2.3243, 0.0541, 0.0541, 1.6757, 5.7297, 9.6216]])
 
 
 @pytest.mark.skipif(