fathom-obstacle-finder.md

layout	title	package	category	tags
reference	fathom_obstacle_finder	fathom_cloud_processor	node	depth sensor obstacle detection point cloud

Description

fathom_obstacle_finder takes in a point cloud from the fathom depth sensor (/cloud, output by depthscan) and generates /obstacle_cloud, a PointCloud2 containing only low and high obstacle points that can be fed to may_nav to allow Kuri to avoid low and high obstacles.

The fathom depth sensor (a PMD time-of-flight sensor array with very custom optics) only illuminates in three regions (the horizontal main beam, which we ignore in this node, the 30-degrees-up cone for clothesline obstacles, and the 30-degrees-down cone for low/cliff obstacles).

This node deals with a few problems with the resulting point cloud, in deciding whether points belong to low/high obstacles:

• There is a fair amount of salt-and-pepper-noise that has to be eliminated
• Detecting what points belong to the floor and what points belong to low obstacles is somewhat tricky due to multipath issues (light from the main beam bouncing off obstacles, hitting the floor, and returning to the sensor) and stray light (from reflections both internal and external to the sensor)
• The centers (elevation-wise) of each of the illuminated beams are more accurate than the weakly illuminated points at the edges of each beam, which often have incorrect/farther-away depth values (also due to multipath and stray light)

Salt-and-pepper-noise is removed by using radius outlier filters (one for clothesline points, two for bump points).

Clothesline/high-obstacle points are then found by taking the nearest point in each azimuthal angular bin, of points that are illuminated by the upward-facing cone.

Bump/low-obstacle points are found by picking out points that are a threshold above "floor" height for each azimuthal angular bin.

The height of the floor in each azimuthal angular bin is estimated using the nearest point in each bin (out of points that are illuminated by the downward-facing cone), with -sensor_height as the max floor height (the floor and low obstacles often appear sunken into the ground in base_footprint frame).

The result is that Kuri will not see low obstacles that are not taller than bump_threshold. But she will also often not see obstacles that are taller than bump_threshold, when she cannot also see the floor in front of the obstacle, or at least the front/leading edge of that obstacle. The idea is that hopefully she will have seen the obstacle at some point while driving up to it.

(Unfortunately, if she is then stuck, navigation-wise, she will clear her costmaps as a recovery behavior, and if she really wants to drive through a low obstacle she can't see the front edge of anymore... she will keep hitting it with her bump sensor. Good thing she is small and harmless and adorable.)

Dependencies

• pcl_conversions
• pcl_ros
• roscpp
• rospy
• sensor_msgs
• std_msgs

Subscribed Topics

/cloud
sensor_msgs::PointCloud2
The full point cloud from the depth sensor, in the frame of the sensor

Published Topics

/obstacle_cloud

sensor_msgs::PointCloud2
Contains low and high obstacle points, to feed to may_nav to allow Kuri to avoid bump and clothesline obstacles

/fathom_obstacle_finder/raw_clothesline_points

sensor_msgs::PointCloud2
Just the clothelsine points, for debugging

/fathom_obstacle_finder/raw_floor_points

sensor_msgs::PointCloud2
The height-adjusted "floor" points, for debugging

Parameters

The following params are found in fathom_cloud_processor/config/fathom_obstacle_finder_params.yaml:

/fathom_obstacle_finder/sensor_height

double, no default
Height of the sensor off the ground

/fathom_obstacle_finder/cliff_min_angle

double, no default
Bottom edge of the elevation angle range for cliff points

/fathom_obstacle_finder/cliff_max_angle

double, no default
Top edge of the elevation angle range for cliff points

/fathom_obstacle_finder/clothesline_min_angle

double, no default
Bottom edge of the elevation angle range for clothesline points

/fathom_obstacle_finder/clothesline_max_angle

double, no default
Top edge of the elevation angle range for clothesline points

/fathom_obstacle_finder/main_beam_height

double, no default
Height of the band used to exclude main-beam points

/fathom_obstacle_finder/max_cliff_point_dist

double, no default
The max xy distance (from the surface of the robot) of a cliff sensor point

/fathom_obstacle_finder/ground_point_max_z_deviation

double, no default
How far down in z can ground points be? (sensor frame)

/fathom_obstacle_finder/min_xy_dist

double, no default
x-y distance to crop obstacle points around the sensor

/fathom_obstacle_finder/x_filter_max

double, no default
Filter out all points farther than this in x

/fathom_obstacle_finder/x_filter_min

double, no default
Filter out all points closer than this in x

/fathom_obstacle_finder/y_filter_max

double, no default
Filter out all points higher than this in y

/fathom_obstacle_finder/y_filter_min

double, no default
Filter out all points lower than this in y

/fathom_obstacle_finder/z_filter_max

double, no default
Filter out all points higher than this in z

/fathom_obstacle_finder/z_filter_min

double, no default
Filter out all points lower than this in z

/fathom_obstacle_finder/bump_threshold

double, no default
Min height of a point above the nearest "ground" point to be a bump obstacle

/fathom_obstacle_finder/radius_outlier_remover_radius

double, no default
Radius outlier remover: radius for noise-filtering raw bump/clothesline points

/fathom_obstacle_finder/radius_outlier_remover_neighbors

int, no default
Radius outlier remover: # of neighboring points required to keep a point

/fathom_obstacle_finder/bump_2nd_outlier_remover_radius

double, no default
2nd stage radius outlier remover radius for filtering bump points

/fathom_obstacle_finder/bump_2nd_outlier_remover_neighbors

int, no default
2nd stage radius outlier remover # of neighboring points required

Launch File

To run, make sure the depth sensor is running and run the depthscan node to generate /cloud (or run a bagfile instead):

$rosrun depthscan depthscan

(or make sure gizmo is running, either way)
and then run

$roslaunch fathom_cloud_processor fathom_processing.launch