feat(slam): add cartographer_ros

2025-07-04 14:39:48 +08:00
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+.. 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.
+
+==========================
+Frequently asked questions
+==========================
+
+Why is laser data rate in the 3D bags higher than the maximum reported 20 Hz rotation speed of the VLP-16?
+----------------------------------------------------------------------------------------------------------
+
+The VLP-16 in the example bags is configured to rotate at 20 Hz. However, the
+frequency of UDP packets the VLP-16 sends is much higher and independent of
+the rotation frequency. The example bags contain a `sensor_msgs/PointCloud2`__
+per UDP packet, not one per revolution.
+
+__ http://www.ros.org/doc/api/sensor_msgs/html/msg/PointCloud2.html
+
+In the `corresponding Cartographer configuration file`__ you see
+`TRAJECTORY_BUILDER_3D.num_accumulated_range_data = 160` which means we
+accumulate 160 per-UDP-packet point clouds into one larger point cloud, which
+incorporates motion estimation by combining constant velocity and IMU
+measurements, for matching. Since there are two VLP-16s, 160 UDP packets is
+enough for roughly 2 revolutions, one per VLP-16.
+
+__ https://github.com/cartographer-project/cartographer_ros/blob/master/cartographer_ros/configuration_files/backpack_3d.lua
+
+Why is IMU data required for 3D SLAM but not for 2D?
+----------------------------------------------------
+
+In 2D, Cartographer supports running the correlative scan matcher, which is normally used for finding loop closure constraints, for local SLAM.
+It is computationally expensive but can often render the incorporation of odometry or IMU data unnecessary.
+2D also has the benefit of assuming a flat world, i.e. up is implicitly defined.
+
+In 3D, an IMU is required mainly for measuring gravity.
+Gravity is an attractive quantity to measure since it does not drift and is a very strong signal and typically comprises most of any measured accelerations.
+Gravity is needed for two reasons:
+
+1. There are no assumptions about the world in 3D.
+To properly world align the resulting trajectory and map, gravity is used to define the z-direction.
+
+2. Roll and pitch can be derived quite well from IMU readings once the direction of gravity has been established.
+This saves work for the scan matcher by reducing the search window in these dimensions.
+
+How do I build cartographer_ros without rviz support?
+-----------------------------------------------------
+
+The simplest solution is to create an empty file named `CATKIN_IGNORE`__ in the `cartographer_rviz` package directory.
+
+__ http://wiki.ros.org/catkin/workspaces
+
+How do I fix the "You called InitGoogleLogging() twice!" error?
+---------------------------------------------------------------
+
+Building `rosconsole` with the `glog` back end can lead to this error.
+Use the `log4cxx` or `print` back end, selectable via the `ROSCONSOLE_BACKEND` CMake argument, to avoid this issue.