Street Crossing

bouncerarcheryAI and Robotics

Nov 14, 2013 (3 years and 7 months ago)

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Street Crossing





marked crosswalk









mobile robot curb cut



Tracking from a moving
platform


Need to look left and right to
find a safe time to cross


Need to look ahead to drive
to other side of road


Must stay in crosswalk

Algorithm for Tracking Cars

1.
Use image differencing method to extract
motion regions

2.
Noise filter using 3x3 median filter; effective for
typical CCD sensor noise

3.
Compute edges of motion regions using Canny
edge detection

4.
Use Mori’s “sign pattern” to find bottoms of
cars [Mori 1994]

5.
Find bounding boxes of moving objects

6.
Use knowledge from prior frames to mark
direction of travel of each bounding box

Mori Sign Pattern


Tracking algorithm uses “Mori Scan” to reliably
detect undersides of cars


The Mori “sign pattern” for vehicle detection
says: the shadow underneath a vehicle is
darker than any other spot on the paved road


The Mori result is invariant to lighting and
holds for wet and dry roads


Use of the Mori result obviates the need for
explicit shadow detection and/or removal;
previously, prominent shadow edges caused
oversize bounding boxes

Mori Sign Pattern


Mori Sign Pattern

Street Crossing

Six frames of a tracking sequence

System Validation


When it is safe to cross, a person monitoring the traffic


scene presses a button


A second button press means it is no longer safe to
cross


The time between button presses specifies a safe
crossing window


Use more than one person to compensate for individual
risk tolerance


Button press data is synchronized with the video data


Compare system safety estimates to human safety
judgments

System Validation


When it is safe to cross, a person monitoring the traffic


scene presses a button


A second button press means it is no longer safe to
cross


The time between button presses specifies a safe
crossing window


Use more than one person to compensate for individual
risk tolerance


Button press data is synchronized with the video data


Compare system safety estimates to human safety
judgments

Crosswalk Traversal


While crossing, devotes more processing
to the right
-
looking video stream


Uses a forward
-
looking camera to detect
and stay on the marked (zebra striped)
crosswalk


Uses sonar to avoid pedestrians and
stopped cars on the crosswalk


Uses a laser range finder to detect the
curb cut; driving over curbs is possible, but
undesirable

Crosswalk Traversal


While crossing, devotes more processing
to the right
-
looking video stream


Uses a forward
-
looking camera to detect
and stay on the marked (zebra striped)
crosswalk


Uses sonar to avoid pedestrians and
stopped cars on the crosswalk


Uses a laser range finder to detect the
curb cut; driving over curbs is possible, but
undesirable

Related Work


Automated driving systems: CMU’s Navlab
project, Dickmanns’ autonomous Autobahn
vehicle, DARPA Challenge


Traffic scene monitoring systems that analyze
traffic conditions


Camera orientation and assumptions of existing
vision
-
based, car
-
tracking systems do not apply
to street crossing


Robotic street crossing has not been done
previously

Reasoning about Bounding Boxes


Larger, lower (in the image plane) bounding
boxes correspond to close cars


Smaller, higher bounding boxes denote distant
cars


Tracking in real time using
Phission

so cars
move very little from frame to frame


Track individual cars over time to determine
speed and travel direction


Need to smooth results over time since CCD
cameras produce noisy data


Research conducted under the auspices
of Dr. Holly A. Yanco, the Robotics Lab,
and the Computer Science Department.




Contact
holly@cs.uml.edu

for additional
information.