Bumblebee

Equitation Elysee

Florian Shkurti — Sat, 03 Sep 2011 23:25:44 +0000

If you are searching for a new activity this semester, and you think you want to give horseback riding a chance, then you can go to the McGill Athletics website and sign up for 1 of 12 available slots. The lessons take place at a school called Equitation Elysee, in a farm in St. Lazare, one-hour drive away from downtown Montreal.

Commuting there by public transportation is next to impossible, but if you don’t have a car, the instructor will put you in contact with other students who do, so you can share the ride. The students range from 5-year olds to 70-year olds, and a previous background is not assumed. The instructor, Jo Sweet, is very experienced, she will tell you when you’re doing things wrong and will help you individually to improve your technique. A typical lesson starts by the student grooming the horse before the ride in the stables, then guiding the horse to the arena for the exercises. I should mention that the purpose of the lessons is to control the gait and speed of the horse, and eventually perform jumps; not to simply go riding along trails. The arena is cool though, and there is classical music playing while you’re training. The school runs all year round, and you can contact Jo even if you’re not a McGill student.

Mathematics and technology

Florian Shkurti — Sat, 03 Sep 2011 22:47:14 +0000

One of the courses I was taking during my third year of undergraduate studies was a full-year Abstract Algebra course, covering among others ring theory and Galois theory in great detail. The course was a requirement for my program, and it was one of the few courses that I was not sure at all I’d enjoy. It turned out that many of my friends in Math enjoyed it, but I didn’t. I felt no, or very few connections with Computer Science (later I discovered through friends that if you study advanced complexity theory and theoretical Computer Science it will be very useful), and as a result I started feeling unmotivated.

At some point during the same year I found a book called “Mathematics and Technology” by Christiane Rousseau and Yvan Saint-Aubin. This book was different, extremely refreshing and motivating. Each chapter is a technological problem that has been solved via applied mathematics. For instance, it presents the math behind: the trilateration of the GPS, the motion of a robotic arm in 3D, error correcting codes, public-key cryptography, Google’s PageRank algorithm, why MP3‘s are sampled at 44.1Khz, the JPEG compression standard, the DNA computer (super-cool chapter!), and many other applications. The book is simply a collection of really interesting problems, accompanied by the mathematical background and principles that allow the reader to understand the basic solutions to those problems. It’s not a perfect or comprehensive book by any means, but it is a beautiful one, in the sense that every chapter is a nicely-told story and the provided theory is strongly tied to each application. I think the mathematical maturity it requires is at most that of a 3rd year undergraduate student in math, though I’m sure you could understand most of it with a basic Calculus and Linear Algebra background.

The American Scholar

Florian Shkurti — Sat, 03 Sep 2011 21:49:06 +0000

Richard Hamming’s “You and your research” is an essay that is often recommended reading for graduate students, as a means of advice from an accomplished scientist. I agree with most of the points he raised: work on the important problems in your field, get the courage to try to solve them, be prepared, be patient and positive etc. There is one point that he made though, which has really bothered me from the day I first read the transcription of his speech:

I had incipient ulcers most of the years that I was at Bell Labs. I have since gone off to the Naval Postgraduate School and laid back somewhat, and now my health is much better. But if you want to be a great scientist you’re going to have to put up with stress. You can lead a nice life; you can be a nice guy or you can be a great scientist.

This really doesn’t make much sense to me. Why does willingness to compromise your health make you a more dedicated scientist? Is a sick or dead scientist better than a healthy one? Is constant stress and fear a prerequisite for being productive and creative? I don’t think they are.

I think I prefer Emerson’s “The American Scholar“.

Ken Robinson on creativity and education

Florian Shkurti — Tue, 26 Apr 2011 13:51:40 +0000

I think this is the first TED talk I ever watched, and it still remains one of my favourites:

Overlaying opencv on ROS

Florian Shkurti — Mon, 31 Jan 2011 02:48:35 +0000

This post is a series of instructions on how to use your own version of the opencv library with ROS. If you’ve had trouble doing this then you’re probably familiar with these instructions — while they are good in general, they are misleading because they assume that you are using the latest version of ROS, which I’d guess is not true for most people. Anyway, here is the story in more detail if you have no idea what these terms refer to:

opencv is an open source computer vision library. It provides implementations of the most popular computer vision algorithms that have appeared in the vision research literature. Needless to say that it evolves very quickly. The latest version is 2.2 and provides support for a large number of feature detectors and descriptors, aside from the classical SIFT and SURF. In case you didn’t know, it also provides face detection and recognition classifiers, image segmentation, object recognition, tracking, and many other goodies.

ROS stands for Robot Operating System. I guess it’s fair to say that its aim is to become for robots what Linux became for computers. ROS is the software platform running on the PR2. It provides support for many sensors and offers abstraction layers that allow roboticists to share code more easily. Code in ROS is organized into entities that are called “nodes,” which communicate with each other by exchanging standardized messages. For instance, ROS offers a node for firewire cameras, which publishes image messages. An image viewing program listens for image messages and when it gets a message it displays it on the screen. The point here is that the communication between the publisher and the listener relies on a standard image message interface, which means that I can write the former and you can write the latter, and we won’t have problems sharing our code. ROS is designed to be distributed, its nodes may run on different machines in the same network. This is all good news, because for the first time (?) the robotics community has a software platform that is very well designed, takes care of most details, and is not going to die soon because of low contribution.

But anyway, I have digressed. This is not a fanboy post about ROS and opencv. My problem was that the latest stable distribution of ROS, called “cturtle,” comes with opencv 2.1, while I wanted 2.2. Since many nodes in ROS depend on opencv, changing its version means that you have to recompile a big part of the system. This page helped a lot, but it didn’t work for me, because it assumed that I was running the latest (unstable?) version of ROS. As a result, compilation was unsuccessful. Here’s what worked at the end:

Create a file called something like cturtle_overlay.rosconfig and paste the following in it:

- svn:
uri: https://code.ros.org/svn/ros-pkg/stacks/vision_opencv/tags/cturtle
local-name: vision_opencv
- svn:
uri: https://code.ros.org/svn/ros-pkg/stacks/image_transport_plugins/tags/cturtle
local-name: image_transport_plugins
- svn:
uri: https://code.ros.org/svn/ros-pkg/stacks/image_pipeline/tags/cturtle
local-name: image_pipeline
- svn:
uri: https://code.ros.org/svn/wg-ros-pkg/stacks/web_interface/tags/cturtle
local-name: web_interface

Create a directory named something like cturtle_overlay on your local workspace.
Run “rosinstall ~/some-path/cturtle_overlay /opt/ros/cturtle ~/some-path/cturtle_overlay.rosconfig”

Edit “~/some-path/cturtle_overlay/vision_opencv/opencv2/Makefile” in order to specify the version of opencv source you’d like to fetch. In my case it was:

SVN_URL = https://code.ros.org/svn/opencv/branches/2.2/opencv
SVN_REVISION = -r4351

Append “source ~/some-path/cturtle_overlay/setup.sh” in your bashrc file, and make sure that the paths in setup.sh are correct.
Run “rosmake -a”

Hopefully, everything will go smoothly after this.

Cool courses

Florian Shkurti — Wed, 05 Jan 2011 01:14:04 +0000

This semester the Computer Science department at McGill is offering a couple of courses for which my friends and I are very excited. The first one is Structure and Dynamics of Networks, which apparently is otherwise known as Network Science, but it really should be called Applied Graph Theory for Large Graphs. Naming aside, the lectures seem to be very promising, as examples will involve networks from different areas, such as biology, political and social science etc.

The second one is Topics in Game Theory, where I believe we’ll study algorithms for selecting strategies to minimize the probability of loss (or maximize the probability of winning) in games where there are many participants. Or at least, that’s what I am expecting — the syllabus doesn’t seem to be posted yet.

Last but not least, the graduate Mobile Robotics class is offered again this year. This course starts with lecture-style material in the first half, during which the students are exposed to motion planning algorithms, sensors, and some fundamental problems in algorithmic robotics. The second half consists of student presentations of research papers. The class is highly interactive and lots of fun.

Planet Ocean

Florian Shkurti — Fri, 10 Dec 2010 22:49:32 +0000

TED videos are fun and educational to watch in general, and this is another excellent example:

The most interesting paradox

Florian Shkurti — Fri, 10 Dec 2010 22:46:33 +0000

Goethe once said: “If you treat a man as he is, you make him worse than he is; if you treat him as if he already were what he potentially could be, you make him what he should be.” If you apply this to yourself it pushes you to overestimate what you think you can do, and attempt what you once thought unreachable. The ancient Greek sages, on the other hand, used to say “Know thyself.” In other words, know your strengths, weaknesses and desires. Both quotes originate from very wise people, and when seen individually they make sense, each on its own merit. The first one pushes you to become a better person, the second one advises you to refrain from juggling knives if you’re juggling for the first time. The paradox arises when you try to take them both into account. How will you draw limits on what you can do and what you can not? How far should you try to push those limits? Hard questions, admitting no generic answers.

Sita sings the blues

Florian Shkurti — Sat, 25 Sep 2010 05:41:31 +0000

When my roommates suggested that I watch this movie, I wasn’t expecting that it was going to be one of the most beautifully made animations that I have ever watched. It is just brilliant:

Don’t skip your guitar lessons

Florian Shkurti — Wed, 25 Nov 2009 02:45:29 +0000

In the beginning of the semester I decided it was time for me to finally take guitar lessons. I had tried in the past to teach myself, but I couldn’t get past the beginner stage. So, when the opportunity arose to take guitar lessons through McGill’s mini courses I seized it and I was really looking forward to them. My instructor was Denis Chang, without a second-thought one of the most talented guitarists and gifted teachers I have ever seen. The man is the ideal teacher: he’s really experienced and knowledgeable, a master in his craft, supportive whenever you need him to be, extremely funny and quite the teaser. Besides, he has some of the coolest guitars I’ve seen. Going to his classes is a real joy. Lessons were held once a week for about two hours and initially there were around ten people registered for the course, but somehow he managed to give individual attention to each of us.

During the last three weeks, though, my coursework and the requirements of my research project didn’t allow much time for me to dedicate to my guitar. I had to skip my three last lessons, but I thought that most other students would attend. Today, which was the day of the last lesson, I decided to go meet Denis and tell him that he’s been a great teacher and he’s made me like the instrument much more. I discovered to my surprise (which is why I’m writing this post) that almost everyone in the class had been skipping the last lessons, just like me. I found Denis waiting for his students in the usual room where we practise (in the SSMU building) playing the piano and killing time. After feeling perplexed that I found none of my classmates there, I started feeling angry and disappointed. It was really depressing to see that one of the best teachers I’ve had was receiving this kind of treatment from his students — myself included, of course. He said that it’s OK, that it’s understandable because it’s the last week of classes and everyone is busy with course work, but that didn’t make me feel better at all. It didn’t seem fair to me that he wouldn’t receive an applause on the last lesson like all good teachers do.

I really like my coursework this semester, and my working hard for the moment is something that just feels right, because I’m doing it for myself and something that I enjoy doing. Yet, this was the first time since I’ve started at McGill that I’ve felt guilty about my efforts. I hope it’s the last. In the meantime, here’s what Denis can do: