37 lines
1.8 KiB
ReStructuredText
37 lines
1.8 KiB
ReStructuredText
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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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==========================
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Frequently asked questions
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==========================
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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?
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----------------------------------------------------------------------------------------------------------------------
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The VLP-16 in the example bags is configured to rotate at 20 Hz. However, the
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frequency of UDP packets the VLP-16 sends is much higher and independent of
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the rotation frequency. The example bags contain a `sensor_msgs/PointCloud2`__
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per UDP packet, not one per revolution.
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__ http://www.ros.org/doc/api/sensor_msgs/html/msg/PointCloud2.html
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In the `corresponding Cartographer configuration file`__ you see
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`TRAJECTORY_BUILDER_3D.scans_per_accumulation = 160` which means we accumulate
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160 per-UDP-packet point clouds into one larger point cloud, which
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incorporates motion estimation by combining constant velocity and IMU
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measurements, for matching. Since there are two VLP-16s, 160 UDP packets is
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enough for roughly 2 revolutions, one per VLP-16.
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__ https://github.com/googlecartographer/cartographer_ros/blob/master/cartographer_ros/configuration_files/backpack_3d.lua
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