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Adds two new FAQ entries. (#515)

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Damon Kohler 2017-09-29 16:06:34 +02:00 committed by GitHub
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docs/source/faq.rst
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@ -16,8 +16,8 @@
Frequently asked questions Frequently asked questions
========================== ==========================
The laser data in the 3D bags is much higher than the maximum reported 20 Hz rotation speed that the VLP-16 can do. Why? 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 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 frequency of UDP packets the VLP-16 sends is much higher and independent of
@ -35,8 +35,8 @@ enough for roughly 2 revolutions, one per VLP-16.
__ https://github.com/googlecartographer/cartographer_ros/blob/master/cartographer_ros/configuration_files/backpack_3d.lua __ https://github.com/googlecartographer/cartographer_ros/blob/master/cartographer_ros/configuration_files/backpack_3d.lua
Why is IMU data required for 3D SLAM, but not for 2D? 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. 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. It is computationally expensive but can often render the incorporation of odometry or IMU data unnecessary.
@ -51,3 +51,16 @@ To properly world align the resulting trajectory and map, gravity is used to def
2. Roll and pitch can be derived quite well from IMU readings once the direction of gravity has been established. 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. This saves work for the scan matcher by reducing the search window in these dimensions.
How do I build cartographer_ros without rviz support?
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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.