Holger Rapp
GitHub
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.. Copyright 2016 The Cartographer Authors
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.. Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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.. http://www.apache.org/licenses/LICENSE-2.0
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.. Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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.. cartographer SHA: 30f7de1a325d6604c780f2f74d9a345ec369d12d
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.. cartographer_ros SHA: 44459e18102305745c56f92549b87d8e91f434fe
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Assets writer
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=============
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The purpose of SLAM is to compute the trajectory of a single sensor through a metric space.
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On a higher level, the input of SLAM is sensor data, its output is the best estimate of the trajectory up to this point in time.
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To be real-time and efficient, Cartographer throws most of the sensor data away immediately.
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The trajectory alone is rarely of interest.
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But once the best trajectory is established, the full sensor data can be used to derive and visualize information about its surroundings.
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Cartographer provides the assets writer for this.
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Its inputs are
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1. the original sensor data fed to SLAM in a ROS bag file,
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2. the cartographer state, which is contained in the ``.pbstream`` file that SLAM creates,
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3. the sensor extrinsics (i.e. TF data from the bag or a URDF),
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4. and a pipeline configuration, which is defined in a ``.lua`` file.
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The assets writer runs through the sensor data in batches with a known trajectory.
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It can be used to color, filter and export SLAM point cloud data in a variety of formats.
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For more information on what the asset writer can be used for, refer to the examples below below and the header files in `cartographer/io`_.
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Sample usage
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------------
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.. code-block:: bash
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# Download the 3D backpack example bag.
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wget -P ~/Downloads https://storage.googleapis.com/cartographer-public-data/bags/backpack_3d/b3-2016-04-05-14-14-00.bag
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# Launch the 3D offline demo.
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roslaunch cartographer_ros offline_backpack_3d.launch bag_filenames:=${HOME}/Downloads/b3-2016-04-05-14-14-00.bag
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Watch the output on the commandline until the offline node terminates.
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It will have written ``b3-2016-04-05-14-14-00.bag.pbstream`` which represents the Cartographer state after it processed all data and finished all optimizations.
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You could have gotten the same state data by running the online node and calling:
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.. code-block:: bash
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# Finish the first trajectory. No further data will be accepted on it.
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rosservice call /finish_trajectory 0
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# Ask Cartographer to serialize its current state.
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rosservice call /write_state ${HOME}/Downloads/b3-2016-04-05-14-14-00.bag.pbstream
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Now we run the assets writer with the `sample configuration file`_ for the 3D backpack:
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.. _sample configuration file: https://github.com/googlecartographer/cartographer_ros/blob/44459e18102305745c56f92549b87d8e91f434fe/cartographer_ros/configuration_files/assets_writer_backpack_3d.lua
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.. code-block:: bash
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roslaunch cartographer_ros assets_writer_backpack_3d.launch \
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bag_filenames:=${HOME}/Downloads/b3-2016-04-05-14-14-00.bag \
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pose_graph_filename:=${HOME}/Downloads/b3-2016-04-05-14-14-00.bag.pbstream
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At the time of writing, the generated assets end up in ``~/.ros``.
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Configuration
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-------------
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The assets writer is modeled as a pipeline.
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It consists of `PointsProcessor`_\ s and `PointsBatch`_\ s flow through it.
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Data flows from the first processor to the next, each has the chance to modify the ``PointsBatch`` before passing it on.
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.. _PointsProcessor: https://github.com/googlecartographer/cartographer/blob/30f7de1a325d6604c780f2f74d9a345ec369d12d/cartographer/io/points_processor.h
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.. _PointsBatch: https://github.com/googlecartographer/cartographer/blob/30f7de1a325d6604c780f2f74d9a345ec369d12d/cartographer/io/points_batch.h
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For example the `assets_writer_backpack_3d.lua`_ uses ``min_max_range_filter`` to remove points that are either too close or too far from the sensor.
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After this, it writes X-Rays, then recolors the ``PointsBatch``\ s depending on the sensor frame ids and writes another set of X-Rays using these new colors.
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.. _assets_writer_backpack_3d.lua: https://github.com/googlecartographer/cartographer_ros/blob/44459e18102305745c56f92549b87d8e91f434fe/cartographer_ros/configuration_files/assets_writer_backpack_3d.lua
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The individual ``PointsProcessor``\ s are all in the `cartographer/io`_ sub-directory and documented in their individual header files.
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.. _cartographer/io: https://github.com/googlecartographer/cartographer/tree/30f7de1a325d6604c780f2f74d9a345ec369d12d/cartographer/io
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First-person visualization of point clouds
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------------------------------------------
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Generating a fly through of points is a two step approach:
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First, write a PLY file with the points you want to visualize, then use `point_cloud_viewer`_.
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.. _point_cloud_viewer: https://github.com/googlecartographer/point_cloud_viewer
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The first step is usually accomplished by using IntensityToColorPointsProcessor_ to give the points a non-white color, then writing them to a PLY using PlyWritingPointsProcessor_.
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An example is in `assets_writer_backpack_2d.lua`_.
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.. _IntensityToColorPointsProcessor: https://github.com/googlecartographer/cartographer/blob/30f7de1a325d6604c780f2f74d9a345ec369d12d/cartographer/io/intensity_to_color_points_processor.cc
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.. _PlyWritingPointsProcessor: https://github.com/googlecartographer/cartographer/blob/30f7de1a325d6604c780f2f74d9a345ec369d12d/cartographer/io/ply_writing_points_processor.h
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.. _assets_writer_backpack_2d.lua: https://github.com/googlecartographer/cartographer_ros/blob/44459e18102305745c56f92549b87d8e91f434fe/cartographer_ros/configuration_files/assets_writer_backpack_2d.lua
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Once you have the PLY, follow the README of `point_cloud_viewer`_ to generate an on-disk octree data structure which can be viewed by one of the viewers in the same repo.
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.. _point_cloud_viewer: https://github.com/googlecartographer/point_cloud_viewer
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@ -18,11 +18,11 @@ Cartographer ROS Integration
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.. toctree::
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:maxdepth: 2
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:hidden:
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configuration
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tuning
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ros_api
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assets_writer
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data
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faq
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