[ros-users] ar_pose basic questions

[Nikhil Karnad]

With regard to a UVC/V4L20-level camera driver...

For some time now at our lab, we have been using this V4L2-based camera
driver with success (GNU GPL v3.0 license). If your kernel (>2.5.x) and
camera (?) support V4L2, this should work for you.

http://code.google.com/p/libv4l2cam/

It comes with a ROS broadcast wrapper for a stereo-camera pair, but we were
able to wrap a separate monocular camera ROS broadcaster as well.

Note that setting the V4L2 camera options in libcam.h is not completely
provided, e.g. we had to add white-balance and gain compensation parameters
ourselves (using linux/videodev2.h, and specifically the structure
v4l2_queryctl with ioctl() calls). Ideally, it would be nice to expose the
getting and setting of these parameters through ROS services.

We don't have a public code repository yet, but it is planned pending a
consolidation effort. I'll try to make this available soon (unless someone
has beaten me to it), so that there aren't as many copies of this as there
are for ARToolkit!

Best,
Nikhil

----
On Sat, Dec 4, 2010 at 11:07 AM, Bill Morris <morris at ee.ccny.cuny.edu>wrote:

> On Fri, 2010-12-03 at 22:49 -0800, Prasad Dixit wrote:
> > Hi,
> >
> > I am trying to run ar_pose node using my webcam logitech pro 9000. I am
> > using only single webcam for pattern detection.
> >
> > According to the wiki page documentation it subscribes /usb_cam/image_raw
> > (sensor_msgs/Image) and
> > (/usb_cam/camera_info)
> >
> > but when i saw the documentation for "usb_cam bosch drivers" it is
> > publishing /usb_cam/image topic.
> >
> > I tried to republish it using republish raw in:=usb_cam/Image
> > out:=usb_cam/image_raw from image_transport node, which has got publish
> but
> > ar_pose seems not subscribing/usb_cam/image_raw topic.
> >
> > Also, i get continuous stream of messages  like below:
> > [swscaler @ 0x87c9be0]No accelerated colorspace conversion found.
> >
> > I could not find much about it but saw some conversion related to it in
> file
> > usb_cam_node.cpp line 91 and onwards
> >
> >    usb_cam_pixel_format pixel_format;
> >     if(pixel_format_name_ == "yuyv")
> >       pixel_format = PIXEL_FORMAT_YUYV;
> >     else if(pixel_format_name_ == "uyvy")
> >       pixel_format = PIXEL_FORMAT_UYVY;
> >     else if(pixel_format_name_ == "mjpeg") {
> >       pixel_format = PIXEL_FORMAT_MJPEG;
> >
> > So, i have questions like,
> > 1. How can i publish usb_cam/image_raw topic?
> > 2. How can i rid off those warnings/ errors? Is FFMPEG creating some
> problem
> > in my case?
> > 3. It is not opening my camera in any viewer in spite of detecting it. I
> > tried to open it using brown gscam package and image_viewer which is
> working
> > fine.
> >
> > Any help is appreciated.
> >
> > Prasad
>
> 1) Perhaps at some point in the future we can get all of the
> stakeholders to unify the USB camera drivers to make one driver that
> works well. You may have better luck with our patched version, or
> someone else's patched version.
> http://robotics.ccny.cuny.edu/git/usb_cam.git
>
> 2) IIRC The color space warning is due to a bug in some version of
> libswscaler. YUYV usually works for me.
>
> 3) I forget way it don't work, I think it's because its missing
> CameraInfo. Try a patched version and see how that goes.
>
> in my mind there should be two webcam drivers for ROS, one for gscam
> which uses gstreamer as the infrastructure layer and one driver that
> uses UVC/V4L2 that should ship with ROS.
>
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>
>
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