要做回航充電，又不想加其他的傳感器，只能靠lidar來(lái)識(shí)別充電樁的形狀定位。
顯然，充電樁表面是平整的直線，那么就要從那么多點(diǎn)中提取直線，然后再識(shí)別哪一條直線是充電樁。
提取直線就成為了最初的一步。
在github上找了半天找到一個(gè)像樣的
https://github.com/kam3k/laser_line_extraction
試了一把，提取效果還不錯(cuò)。
記錄一下并把配置說(shuō)明一下：
topics
訂閱的topic顯然是 scan，發(fā)布了兩個(gè)topic，我們要用的是/line_segments，/line_markers是用來(lái)在rviz上顯示的，可以在launch中關(guān)閉。
配置
配置列表如下，基本上都好理解，被我分成了三大類(lèi)，便于理解。
frame_id (default: "laser") # The frame in which the line segments are published.
scan_topic (default: "scan") # The LaserScan topic.
publish_markers (default: false) # Whether or not markers are published.
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bearing_std_dev (default: 0.001) # The standard deviation of bearing uncertainty in the laser scans (rad).
least_sq_angle_thresh (default: 0.0001) # Change in angle (rad) threshold to stop iterating least squares (least_sq_radius_thresh must also be met).
least_sq_radius_thresh (default: 0.0001) # Change in radius (m) threshold to stop iterating least squares (least_sq_angle_thresh must also be met).
range_std_dev (default: 0.02) # The standard deviation of range uncertainty in the laser scans (m).
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max_line_gap (default: 0.4) # The maximum distance between two points in the same line (m).
min_line_length (default: 0.5) # Lines shorter than this are not published (m).
min_line_points (default: 9) # Lines with fewer points than this are not published.
min_range (default: 0.4) # Points closer than this are ignored (m).
min_split_dist (default: 0.05) # When performing "split" step of split and merge, a split between two points results when the two points are at least this far apart (m).
# 線段split的閾值，過(guò)大時(shí)很多線段被合并成一條，過(guò)小時(shí)，出現(xiàn)很多碎短的線段
outlier_dist (default: 0.05) # Points who are at least this distance from all their neighbours are considered outliers (m).
消息
最重要的是我們拿到 /line_segments的消息之后如何分析
消息類(lèi)型是LineSegmentsList，如下，這不是主要的。
每個(gè)segment的類(lèi)型LineSegment才是最主要的：
這其中的start, end都好理解：
start 和end分別是這個(gè)線段的起點(diǎn)坐標(biāo)和終點(diǎn)坐標(biāo)
radius和angle就不好理解了，于是我們echo了它的消息，如下
radius: 0.752869129181
angle: -0.797926008701
covariance: [1.8016297644862789e-06, 1.2701141258730786e-06, 1.2701141258730786e-06, 9.006992058857577e-07]
start: [-0.6120783090591431, -1.648557186126709]
end: [-0.35934978723526, -1.402082920074463]
-
radius: 1.1387783289
angle: -0.808640360832
covariance: [2.9355262540775584e-06, 2.777204372250708e-06, 2.777204372250708e-06, 2.649457655934384e-06]
start: [-0.08191638439893723, -1.6525081396102905]
end: [0.14225095510482788, -1.4385261535644531]
-
radius: 1.12730681896
angle: -0.787253201008
covariance: [1.4751535672985483e-06, -2.180588808187167e-06, -2.180588808187167e-06, 3.510540864226641e-06]
start: [1.011875033378601, -0.5831754803657532]
end: [1.459415078163147, -0.1372928023338318]
-
radius: 3.53375911713
angle: 0.791161239147
covariance: [3.9494702832598705e-06, -7.934396307973657e-06, -7.934396307973657e-06, 2.223481897090096e-05]
start: [2.499594211578369, 2.497988224029541]
end: [1.9661375284194946, 3.025331497192383]
我的地圖總共擬合出4條直線，相應(yīng)的結(jié)果如下，中間的frame是laser的frame，紅色為x軸+，
按照ros中的坐標(biāo)系來(lái)說(shuō)，機(jī)器人正前方為0度，逆時(shí)針為正，激光數(shù)據(jù)的排列是從-135~135度（我的激光掃描范圍是270度），那么上面4個(gè)線段從左往右依次是1,2,3,4。
這樣的話我們就能理解 radius和angle的意思了。官方給的解釋是極坐標(biāo)下參數(shù)，我們能夠理解到的是
angle： 原點(diǎn)到直線的垂線的角度，角度以機(jī)器人為坐標(biāo)系計(jì)算，范圍是-PI~PI
radius： 原點(diǎn)到直線的距離
根據(jù)這兩個(gè)參數(shù)，完全不能確定什么，這兩個(gè)參數(shù)完全能夠根據(jù)start和end點(diǎn)計(jì)算出來(lái)。不理解這兩個(gè)參數(shù)存在的意義。
- covariance是2X2的矩陣，是radius和angle的協(xié)方差
