Archive for January, 2012


Range find(h)er!

So the past few weeks I’ve been working on this really interesting project for creating a 3D mobile car environment in real time for teleop (and later autonomous movement). It starts with calibrating a 3D laser rangefinder’s data and a monocular camera’s feed which allows me, after the calibration is done, to map each coordinate in my image to a 3D point in the world coordinates (within the range of my rangefinder, of course). So, any obstacles coming up in the real world environs can then be rendered accurately in my immersive virtual environment. Now since everything’s in 3D the operator’s point of view can be moved around to any required orientation. So, for instance, while parking all that is needed to be done is to shift to an overhead view. In addition, since tele op is relatively laggy, the presence of this rendered environment gives the op a fair idea of the immediate environment, and the ability to continue along projected trajectories rather than stopping for resumption of connection.

So, as the SICK nodder was taking some time to arrive, I decide to play around Gazebo, and simulate the camera, 3D Laser rangefinder and the checkerboard pattern for calibration within it, and thus attempt to calibrate the camera-rangefinder pair from within the simulation. In doing so, I was finally forced to shift to ubuntu (Shakes fist at lazy programmers) which, although smoother, isn’t entirely as bug free as it is made out to be. So, I’ve created models for the camera and rangefinder and implemented gazebo dynamic plugins within them to simulate them. I’ve also spawned a checkerboard textured box, which using a keyboard manipulated node I move around the environment. So this is what it looks like right now

Screenshot of w.i.p.

So here, the environment is in the Gazebo window at the bottom, where I've (crudely) annotated the Checkerboard, camera and Laser Rangefinder. There are other bodies to provide a more interesting scan. The point cloud of the scan can be seen in the rviz window in the center, and the camera image at the right. Note the displacement between the two. The KeyboardOp node is running in the background at the left, listening for keystrokes, and a sample HighGui window displaying the detected Chessboard Corners at the top Left.

Looks optimistic!

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Fedora 16

So yesterday I decided to preupgrade fc 15 to 16. And,as always, fedora didn’t disappoint in coming up with issues. Although it downloaded the required packages all fine, on reboot, anaconda fired up and fell through on not being able to install qt-examples, and since it represented a possible media failure from the (local) repo, it decided to fatal error on me, dropping to a non responsive screen.
Fortunately, I could shift to tty2 (Alt+F2) where I got anaconda’s bash. I chrooted to /mnt/sysimg to get to my fedora install, and yum removed qt-examples. This done, I rebooted to find anaconda chugging along fine.
As expected, that wasn’t the end. Since fc16 has implemented grub2 by default, anaconda tried to update grub, but because my Dell Utility partition didn’t leave any space at the beginning of the drive, it failed. So I booted up fc15, which fortunately had not been removed, and gparted the Dell utility partition off. I then made the grub2 config and installed it to /dev/sda. Success!
Not. So, I happily logged in to FC 16, and it was only when I accessed my yum repos, I realized that they were still fc15. After trying yum clean all and makecache, I looked up on the net to find that I needed to reinstall fedora-release. a yum reinstall fedora-release threw up an error "Error: Protected multilib versions: fedora-release-15-3.noarch != fedora-release-16-1.noarch"
After a lot of looking around, realized that the issue lay in the fact that somehow yum was getting $releasever wrong all the time. So, as a workaround, created a releasever file in /etc/yum/vars with 16 in it. Voila!
I then had to erase all the duplicates on my system that amounted to over 5.5 GB(!) using package-cleanup --cleandupes. Additionally, to  avoid dependency hell I had to remove all my boost library installs.

Update: You can follow the rest of the development on this page. I don’t like it.