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cs:slam:start [2019/05/01 13:47] Steve Hemm [How it Works] |
cs:slam:start [2019/08/18 16:20] Steve Hemm [Tracking] |
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| - | ====== SLAM (Page still under construction) ====== | + | ====== SLAM ====== |
| ====== Simultaneous Localization and Mapping ====== | ====== Simultaneous Localization and Mapping ====== | ||
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| {{:cs:slam:orb2.png}} | {{:cs:slam:orb2.png}} | ||
| - | ORB-SLAM2 is a feature based algorithm that takes keyframes from video output and extracts keypoints or features(such as corners), and uses them to establish location of the sub and its surroundings. | + | ORB-SLAM2 is a feature based algorithm that takes keyframes from video output and extracts keypoints or features (such as corners), and uses them to establish location of the sub and its surroundings. |
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| + | It consists of three main modules: Tracking, Local Mapping, and Loop Closing. | ||
| ==== Tracking ==== | ==== Tracking ==== | ||
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| + | -Tracking localizes the camera by comparing features in a local map. | ||
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| + | -Detects features using the [[https://docs.opencv.org/3.0-beta/doc/py_tutorials/py_feature2d/py_fast/py_fast.html|FAST Algorithm]]. | ||
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| + | -Describes features using [[https://opencv-python-tutroals.readthedocs.io/en/latest/py_tutorials/py_feature2d/py_orb/py_orb.html|ORB Algorithm]]. | ||
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| + | -Selects a new keyframe. | ||
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| + | -If localization is lost, uses Place Recognition module to relocate. | ||
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| ==== Local Mapping ==== | ==== Local Mapping ==== | ||
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| + | -Keyframes are added to co-visibility graph Spanning Tree. | ||
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| + | -New Map points are creates by triangulating matching ORB features from different keyframes. | ||
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| + | -Validity of map point is checked by seeing if it is found in other keyframes where it is predicted to be. Must be seen by at least 3 other keyframes. | ||
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| ==== Loop Closing ==== | ==== Loop Closing ==== | ||
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| + | -Loop closing is when the sub recognizes that it has returned to a previous location and adjust map points to accommodate. | ||
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| + | -To detect possible loops, check bag of words vectors in Place Recognition module of the current keyframe and its neighbors in the co-visibility graph. | ||
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| + | -If loop candidate is found preform similarity transform. | ||
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| + | -Fuse map points and preform bundle adjustment. | ||
| ==== Map ==== | ==== Map ==== | ||
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| + | Each map point stores: | ||
| + | *Its 3D position in the world coordinate system. | ||
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| + | *ORB descriptor. | ||
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| + | *The maximum dmax and minimum dmin distances at which the point can be observed, according to the scale invariance limits of the ORB features. | ||
| ==== Place Recognition ==== | ==== Place Recognition ==== | ||
