learning to optimally segment point cloudspeiyunh/opcseg/slides.pdf · ! = 0.5m! = 0.25m *colors...
TRANSCRIPT
Learning to Optimally Segment Point Clouds
Peiyun Hu, David Held, Deva Ramanan
Carnegie Mellon University
Paper ID: 2977
Raw LiDAR ScansToday, most autonomous vehicles perceive the world through LiDAR point clouds.
Map-based Preprocessing
*We focus on a limited field of view in this work.
They often use pre-built maps to first filter out points from the background, then run clustering on points from the foreground to obtain object-level perception.
Object-level PerceptionHowever, it is often hard to set the right hyper-parameters for clustering. For example,
Euclidean Clustering with a large distance threshold tends to under-segments pedestrians.
*Colors flicker because the algorithm does not track objects across time.
Object-level PerceptionAnd Euclidean Clustering with a small distance threshold tends to over-segments vehicles.
*Colors flicker because the algorithm does not track objects across time.
No One-Fits-All Solution
= 2.0mε = 1.0mε
= 0.5mε = 0.25mε
*Colors across parameters do not indicate correspondence.
The best distance threshold often varies from scenario to scenario.
A Hierarchical Perspective
= 2.0mε = 1.0mε = 0.5mε = 0.25mε
Segmentations with different thresholds form a hierarchy, where nodes represent segments.
Learning Objectness Models
PointNet++ (Qi et al., NeurIPS’17)
We learn a model to predict an objectness score for each segment in the hierarchy.
Bad
Good
0.9
0.1
ObjectnessHow well a segment overlaps with ground truths.
Searching for OptimalityGiven a hierarchy of segments with scores, we search for the optimal segmentation.
Bad
Good
Bad
Good
defines
Optimal Worst-case SegmentationWe propose an efficient algorithm that produces optimal segmentation under this definition.
the worst segment score segmentation score
Bad
Good
defines
Average-case SegmentationWe also propose an efficient algorithm guided by average-case score.
average local segment score global segmentation score
Quantitative EvaluationProtocol: compute the percentage of objects that are under-segmented and over-segmented.
U = 1L
L
∑l=1
1[|Ci* ∩ Cgt
l ||Ci* |
< τU]
2 under-segmented pedestrians 1 over-segmented car
O = 1L
L
∑l=1
1[|Ci* ∩ Cgt
l ||Cgt
l |< τO]
Assumption: output is a valid partition.
Held et al., RSS’15
Segmentation Errors(1) As distance threshold increases, more under-segmentation and less over-segmentation.
(2) Our adaptive algorithm significantly outperforms each single-parameter baseline. (3) We also plot the lower-bound errors for the search space, showing room for improvement.
0
0.25
0.5
0.75
1
Under Over Total
13%5%8%
17%8%9%
19%6%
13%
28%
5%
23%35%
25%
9%
68%65%
3%
92%91%
1%
CC(0.25m) CC(0.5m) CC(1m) CC(2m) Ours(min) Ours(avg) CC(*)
No One-Fits-All Solution
= 2.0mε = 1.0mε
= 0.5mε = 0.25mε
*Colors across parameters do not indicate correspondence.
The best distance threshold often varies from scenario to scenario.
Algorithmic OutputOur algorithm can adaptively choose the best distance threshold for each scenario.
https://cs.cmu.edu/~peiyunh/opcseg