fix infinite loop in segment_plane if num_points < ransac_n

cpp/open3d/geometry/PointCloudSegmentation.cpp

@@ -43,7 +43,6 @@ class RandomSampler {
                 valid_sample++;
             }
         }
-
         return samples;
     }
 
@@ -156,21 +155,7 @@ std::tuple<Eigen::Vector4d, std::vector<size_t>> PointCloud::SegmentPlane(
         utility::LogError("Probability must be > 0 and <= 1.0");
     }
 
-    RANSACResult result;
-
-    // Initialize the best plane model.
-    Eigen::Vector4d best_plane_model = Eigen::Vector4d(0, 0, 0, 0);
-
     size_t num_points = points_.size();
-    RandomSampler<size_t> sampler(num_points);
-    // Pre-generate all random samples before entering the parallel region
-    std::vector<std::vector<size_t>> all_sampled_indices;
-    all_sampled_indices.reserve(num_iterations);
-    for (int i = 0; i < num_iterations; i++) {
-        all_sampled_indices.push_back(sampler(ransac_n));
-    }
-
-    // Return if ransac_n is less than the required plane model parameters.
     if (ransac_n < 3) {
         utility::LogError(
                 "ransac_n should be set to higher than or equal to 3.");
@@ -183,6 +168,16 @@ std::tuple<Eigen::Vector4d, std::vector<size_t>> PointCloud::SegmentPlane(
                                std::vector<size_t>{});
     }
 
+    RANSACResult result;
+    Eigen::Vector4d best_plane_model = Eigen::Vector4d(0, 0, 0, 0);
+
+    RandomSampler<size_t> sampler(num_points);
+    std::vector<std::vector<size_t>> all_sampled_indices;
+    all_sampled_indices.reserve(num_iterations);
+    for (int i = 0; i < num_iterations; i++) {
+        all_sampled_indices.push_back(sampler(ransac_n));
+    }
+
     // Use size_t here to avoid large integer which acceed max of int.
     size_t break_iteration = std::numeric_limits<size_t>::max();
     int iteration_count = 0;