72 lines
2.6 KiB
ReStructuredText
72 lines
2.6 KiB
ReStructuredText
.. Copyright 2017 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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Terminology
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===========
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This documents a few common patterns that exist in the Cartographer codebase.
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Frames
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======
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global map frame
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This is the frame in which global SLAM results are expressed. It is the fixed
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map frame including all loop closure and optimization results. The transform
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between this frame and any other frame can jump when new optimization results
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are available. Its z-axis points upwards, i.e. the gravitational acceleration
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vector points in the -z direction, i.e. the gravitational component measured
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by an accelerometer is in the +z direction.
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local map frame
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This is the frame in which local SLAM results are expressed. It is the fixed
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map frame excluding loop closures and the pose graph optimization. For a given
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point in time, the transform between this and the global map frame may change,
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but the transform between this and all other frames does not change.
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submap frame
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Each submap has a separate fixed frame.
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tracking frame
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The frame in which sensor data is expressed. It is not fixed, i.e. it changes
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over time. It is also different for different trajectories.
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gravity-aligned frame
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Only used in 2D. A frame colocated with the tracking frame but with a
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different orientation that is approximately aligned with gravity, i.e. the
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gravitational acceleration vector points approximately in the -z direction. No
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assumption about yaw (rotation around the z axis between this and the tracking
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frame) should be made. A different gravity-aligned frame is used for different
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trajectory nodes, e.g. yaw can change arbitrarily between gravity-aligned
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frames of consecutive nodes.
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Transforms
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==========
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local_pose
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Transforms data from the tracking frame (or a submap frame, depending on
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context) to the local map frame.
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global_pose
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Transforms data from the tracking frame (or a submap frame, depending on
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context) to the global map frame.
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local_submap_pose
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Transforms data from a submap frame to the local map frame.
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global_submap_pose
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Transforms data from a submap frame to the global map frame.
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