3.3.1 Eliminating the influence of rough road: To eliminate
the influence of rough roads, a technology which is similar with the difference of Digital Surface Model DSM and Digital
Terrain Model DTM is used. The technology has three key steps:
Divide the point clouds into small grid
Calculate the minimum value along z-axis for each grid
Each point clouds in grid minus the minimum z value Figure 4 shows results of eliminating rough road.
Figure 4. Eliminating the influence of rough road
3.3.2 Rough Segmentation: As shown in figure 5a, the
rough segmentation has four key steps. Firstly, we fit a plane Π
from the partitioned data based on RANSAC algorithm. If the distance D
i
P
i,
Π of a point P
i
to the plane Π
is less than a threshold
α, the point P
i
is called inlier, otherwise called outlier. The conditions can be described as
D
i
P
i,
Π α 1
The set of inliers is called rough plane. Secondly, multiple refined planes
Π
i
are extracted from rough plane using the same method with different thresholds
β
i
. Thirdly, rough road edge points could be extracted by combination of rough plane and each
refined plane. We search inliers near an outlier. If there exist an inlier, and then the outlier is considered to be a road edge point.
Therefore, we can get multiple rough road edges due to multiple refined planes. At last, the best candidate road edge points are
extracted by comparing
the energy Ε
s
about smoothness for different rough road edge points. The energy can be described as
Ε
s
= σ e
i
, t
i
2 where
σ = variance e
i
= candidate road edge point t
i
= nearest trajectory point to e
i
The segmentation are presented on figures 5b, 5c, 5d and 5e. It can be seen that the road edge points are well extracted,
although some points could be wrong classified. The proposed method is quite robust and almost no additional assumptions.
3.4
Refined Road Edge Extracting
The detected candidate road edge points are discontinuous and do not contain topology. It is necessary to track and refine these
points. The proposed method uses the geometric patterns of road to refine the road edge points, which has two key steps:
Refining based on stable road width
Refining based on road continuity
3.4.1 Refining based on road width: We construct an
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