UAV Obstacle Detection

1
UAV Obstacle Detection

• For most UAV applications (gt50 m), the obstacles
  of concern will be large objects such as towers,
  buildings or large trees
• For these cases, the problem of obstacle
  detection is different from that of ground
  vehicles in environments cluttered with many
  obstacles.

VS
2
Sky Segmentation for Detection

• We propose that we can detect large obstacles by
  a simple segmentation of the sky in the image,
  treating non sky as obstacles
• This method is computationally inexpensive
  compared to triangulation methods making it
  advantageous to small UAVs with limited
  computational power
• Detection of large obstacles lends itself to
  simple obstacle avoidance methods for scarce
  obstacles

3
Sky Segmentation by Region Growing

• Region growing works well for grouping large low
  textured regions such as the sky
• Superior to pure color segmentation since sky is
  typically not uniform color

4
Region Growing Algorigthm

• Add a single seed pixel to the que
• While (que not empty)
• For each of 8 neighbor pixels
• If neighbor pixel satisfies homogeneity
  constraint and is unassigned, set neighbor pixel
  to current region and add to que
• If several large regions are found, they can be
  combined using simple region statistics using
  color averages, histograms, etc.
• Local homogeneity constraints such as threshold
  on color and intensity values allows gradual
  change over region

5
Sky Segmentation Results
6
Results
7
Avoidance with Side Slip

• For an aircraft that uses side slip to avoid
  obstacles, the angular information alone can be
  used for avoidance method
• Advantage of sideslip is that the plane doesnt
  look away from path and it allows smaller
  deviations from path
• Disadvantage of sideslip is that it is less
  aggressive than full turn

8
Avoidance with Side Slip

• For an airplane using sideslip, the forward
  reachable set is a cone, whose width depends on
  the maximum sideslip velocity
• If the for a forward velocity VF and a maximum
  sideslip velocity VS, the size of the cone is

9
Avoidance with Side Slip

• As long as the obstacle doesnt completely fill
  the forward reachable set cone in front of the
  aircraft, some sideslip command that will allow
  the aircraft to avoid the obstacle
• The angle of the obstacle can be found directly
  from the camera since cameras produce angular
  measurements

Safe path
10
Obstacle Avoidance

• The looming of the non sky segments can be used
  to calculate the distance to the object and
  object width if the aircraft velocity is known
  and the foreshortening of the object is small
  enough
• This information can be used by existing
  avoidance methods (Frew 04)