Monthly Archives: May 2010

OpenSLAM

SLAM, software

This is a map of the University of Freiburg Campus generated with Gmapping. Conveniently enough, a wrapper has been made for GMapping to work with ROS and someone has written a tutorial on it.

This image shows the results of the TreeMap Algorithm. This has not been ported to ROS, yet.

Code for these and many more simultaneous localization and mapping (SLAM) algorithms are available at OpenSLAM.org.

Testing: ROS USB Camera drivers

logitech, ROS, testing, usb, webcam

So evidently as a sign of desperation, the developers of the robotics framework that shall not be named have decided to reduce its price to $0. They might have better luck finding developers if they tried using an open source license, but that kinda defeats the purpose of locking developers into using your code, tool chain, OS and etc. As they say, I wouldn’t use it if you paid me, because it would just cost me too much in the long run. Also, they have not provided me with an xBox or a Project Natal controller, so really it’s their own fault that I have nothing good to say.

Meanwhile ROS appears to have the opposite problem, with multiple developers writing drivers that perform the same basic tasks. I suppose it’s better to have too many options than too few but figuring out which driver to use can take some time. So to save you time and energy we will be testing and rating various ROS drivers to save you time and energy.

This week we are testing USB camera drivers for performance and functionality.
Here are the options we are testing.

Probe
The probe driver, from the Brown Robotics Group, uses GStreamer to broadcast data to an image topic. The upside of this is that it is very flexible and it is easy to connect to just about any camera. It can also be used to connect to more than just cameras, for example with the right incantations it can be used to connect to things like mjpeg streams sent over http.

On the downside, figuring out the right incantations to get anything to work can take a while. One option is to launch the driver from a terminal, which may make it easier to get GStreamer setup.

$ export PROBE_CONFIG="v4l2src device=/dev/video1 ! video/x-raw-rgb, width=320, height=240, framerate=30/1 ! ffmpegcolorspace ! identity name=ros ! fakesink"
$ rosrun probe probe

probe launch file

usb_cam
Developed by the Bosch Research and Technology Center for their Segway RMP based robot, the usb_cam driver offers good performance and reasonable configuration options. It is also the only driver considered that currently support the camera_info topic. Unfortunately it doesn’t support saving the calibration to a file via set_camera_info. So tricking the camera calibration process into working in the boxturtle release requires editing the source.

~/ros/stacks/image_pipeline/camera_calibration/nodes/cameracalibrator.py

...

class CalibrationNode:

    def __init__(self, chess_size, dim):
        # assume any non-default service names have been set.  Wait for the service to become ready
#        for svcname in ["camera", "left_camera", "right_camera"]:
        for svcname in ["left_camera", "right_camera"]:
            remapped = rospy.remap_name(svcname)
            if remapped != svcname:
                fullservicename = "%s/set_camera_info" % remapped

...

usb_cam launch file


    
        
        
        
        
        
        
        [0.032095, -0.238155, 0.000104, -0.002138, 0.0000]
        [723.715912, 0.000000, 318.180121, 0.000000, 719.919423, 280.697379, 0.000000, 0.000000, 1.000000]
        [1.0, 0.0, 0.0, 0.0, 1.0, 0.0, 0.0, 0.0, 1.0]
        [723.715912, 0.000000, 318.180121, 0.000000, 0.000000, 719.919423, 280.697379, 0.000000, 0.000000, 0.000000, 1.000000, 0.000000]

uvc_cam
Developed at the Stanford AI Lab, the uvc_cam driver may not have the highest performance but it seems to have more of the camera controls implemented. It also has some interesting support tools included, including a program that can be used to enumerate the available camera devices.

uvc_cam launch file

gencam_cu
Over at Colorado University they have developed the gencam_cu driver. This driver uses OpenCV to access the camera. The driver has pretty good performance however there appears to be no way to configure the resolution. It does however support compressed_image_transport which is convenient.

gencam_cu launch file

logitech_usb_webcam
Actually, this isn’t another driver, it’s just some launch files that work with usb_cam.

USB Ports

While it may seem like all USB ports are the same, depending on the bus topology and USB version, each USB port may provide vastly different performance. In some configurations testing showed a significant difference, with one USB port capable of providing 15 frames per second while another port provided 30 frames per second. You would think that two ports adjacent to each other would be on the same bus, but apparently not.

Performance
High resolution images at high frame rates tend to pin the CPU at 100% or more, which doesn’t particularly make sense but that is software for you. There are probably some low hanging fruit in terms of optimizations, however they may be deep within the V4L2 stack. Profiling and optimization is left for those whose projects depend on it.

PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
1234 user      20   0  117m  34m 8992 R  110  1.7   0:23.92 probe

Camera Calibration
Out of all of these drivers, only the usb_cam driver currently supports the camera_info topic. Without this information, image rectification using image_proc will not work unless you write your own camera_info publisher. Fortunately the camera_info_manager support class appears to be shipping with the next stable release of ROS. This should help camera driver developers implement the camera_info topic consistently and improve the camera calibration process.

Cameras Tested
The following cameras were tested at 640×480 and 320×240 with 24 bit color. Most modern USB cameras that support the USB Video Class (UVC) interface should work.

  • Logitech C600
  • Logitech Quickcam 9000 Pro
  • Built-in Laptop OmniVision OV2640 Webcam

Testing
For all of these tests, image_view is run at the same time as the camera driver to produce a simulated load and to ensure that the video is actually being transmitted.

Combo launch file

The rostopic command is used to measure the update frequency of the camera image messages.

$ rostopic hz --window=1000 /image_raw

Results

320x240  C600   9000 Pro OV2640
Probe    29.942 29.945   15.006
usb_cam  30.035 30.036   7.503
uvc_cam  25.082 24.077   15.006

640x480    C600    9000 Pro  OV2640
Probe      11.914  12.373    12.807
usb_cam    15.068  15.026    10.005
uvc_cam    12.651  12.851    8.267
gencam_cu  14.711  14.974    7.503

Conclusion
Overall each driver contains features and ideas not found in other drivers. Moving forward it would probably be in everyone’s interest to focus on improving the performance of one of the drivers and to incorporate the best ideas from the other drivers. The usb_cam driver looks to be the best supported and may be an ideal starting point, however the bsd license may be a minor issue for some.

If you are trying to get a USB camera working with ROS, it is suggested that you start with the usb_cam driver and if that doesn’t work for you, try one of the other drivers.

If you don’t have ROS installed, instructions are here and if you have time I strongly suggest trying the tutorials. Now would be a great time to get ROS setup because later this week we will be showing you how to connect OpenCV to ROS to perform actual practical robotics tasks.