Adds a PureLocalizationTrimmer.

Related to cartographer-project#315.

cartographer/mapping/pose_graph_trimmer.cc

@@ -0,0 +1,41 @@
+/*
+ * Copyright 2016 The Cartographer Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "cartographer/mapping/pose_graph_trimmer.h"
+
+#include "glog/logging.h"
+
+namespace cartographer {
+namespace mapping {
+
+PureLocalizationTrimmer::PureLocalizationTrimmer(int trajectory_id,
+                                                 int num_submaps_to_keep)
+    : trajectory_id_(trajectory_id), num_submaps_to_keep_(num_submaps_to_keep) {
+  CHECK_GT(num_submaps_to_keep, 0);
+}
+
+void PureLocalizationTrimmer::Trim(TrimmingInterface* trimming) {
+  const int total_num_submaps = trimming->num_submaps(trajectory_id_);
+  while (total_num_submaps > num_submaps_trimmed_ + num_submaps_to_keep_) {
+    const int submap_index_to_trim_next = num_submaps_trimmed_;
+    trimming->MarkSubmapAsTrimmed(
+        SubmapId{trajectory_id_, submap_index_to_trim_next});
+    ++num_submaps_trimmed_;
+  }
+}
+
+}  // namespace mapping
+}  // namespace cartographer

cartographer/mapping/pose_graph_trimmer.h

@@ -47,6 +47,21 @@ class PoseGraphTrimmer {
   virtual void Trim(TrimmingInterface* trimming) = 0;
 };
 
+// Keeps the last 'num_submaps_to_keep' of the trajectory with 'trajectory_id'
+// to implement localization without mapping.
+class PureLocalizationTrimmer : public PoseGraphTrimmer {
+ public:
+  PureLocalizationTrimmer(int trajectory_id, int num_submaps_to_keep);
+  ~PureLocalizationTrimmer() override {}
+
+  void Trim(TrimmingInterface* trimming) override;
+
+ private:
+  const int trajectory_id_;
+  const int num_submaps_to_keep_;
+  int num_submaps_trimmed_ = 0;
+};
+
 }  // namespace mapping
 }  // namespace cartographer