Monday, October 22, 2012

Beaglebone: Installing Ubuntu 12.10

I've got my hands on a Beaglebone, and the first thing I did was installing the latest Ubuntu 12.10 on it. Here how I proceeded.

This post is mainly for self-documenting, feel free to follow my footsteps at your own risk. These steps will probably also work on the Beagleboard.

Back up the original image

The Beaglebone comes with the Linux Ångström distribution. So I backed up the original image, in case something failed. Even if I were to stick with the Ångström distro, it's a good idea to back up the original image.

I removed the microSD that shipped with the Beaglebone, and inserted it into my PC SD slot. Then I checked in which partition it got mounted, using the following command.
df -l
/dev/sda is my PC harddrive, and /dev/sdb is the Beaglebone SD card.

After identifying where the SD was mounted, I used the following command to backup the SD.
dd if=/dev/<sdx> | gzip > /path/to/image.gz
In case I needed to restore the image, I'll have to use the following command:
gzip -dc /path/to/image.gz | dd of=/dev/<sdx>

Installing Ubuntu

I followed the instructions from elinux. These are the summarized steps:
  • Download the minimal Ubuntu 12.10 image
cd ~/Desktop
  • Verify the integrity of the image
md5sum ubuntu-12.10-r2-minimal-armhf-2012-11-29.tar.xz
Which should match the following output
b0ee1964a3f8196f4f1a501d1d2ac83a ubuntu-12.10-r2-minimal-armhf-2012-11-29.tar.xz
  • Untar the package
tar xJf ubuntu-12.10-r2-minimal-armhf-2012-11-29.tar.xz
cd ubuntu-12.10-r2-minimal-armhf-2012-11-29
  • Flash the image into your SD
sudo ./ --mmc /dev/<sdx> --uboot bone

Finished flashing the Ubuntu image into the SD card.

For the record (Older releases):

Release 1:
MD5: 31be6761a37af98906c5c1e892601e85

Connecting to your Beaglebone

After flashing the Ubuntu image, I removed the SD from my PC and plugged it back into the Beaglebone. I decided to make the first connection using the tty over USB.

After connecting the Beaglebone to my PC using a USB cable, I had to figure out the exact name of the ttyUSBx with the following command.
dmesg | grep ttyUSB
From documentation, ttyUSB0 -> JTAG, ttyUSB1 -> UART (terminal)

I used GNU screen to stablish the connection:
sudo apt-get install screen
screen /dev/<ttyUSBx> 115200
After the connection was established. I saw no output so I pressed the reset button on the Beaglebone.


The default login information is below.
  • login: ubuntu
  • password: temppwd

Things to do after installing Ubuntu

OK, I logged in! ... Now what?

Change your password

First thing first, I changed the default password to something stronger
# On the Beaglebone

Connect the Beaglebone to the internet

I plugged an Ethernet cable into the Beaglebone, and checked if the connection was OK.
# On the Beaglebone
I let ping run for a while and then I finished it with Ctrl+C.
Notice the "0% packet lost", that's a Win.

OK I lied, it didn't work the first time, I got 100% packet lost, but resetting the Beaglebone solved the problem.


Next, I enabled bash completion - a.k.a. the tab autocompletion:
# On the Beaglebone
sudo apt-get update && sudo apt-get install bash-completion

Change the hostname

The terminal prompt says "ubuntu@arm". This means the Beaglebone hostname is "arm". I changed that with the following commands.
# On the Beaglebone
cat /etc/hosts
I got the following output.
# On the Beaglebone localhost arm
So I changed the second line with:
# On the Beaglebone
sudo nano /etc/hosts
# changed the second line from arm to <new-hostname>
Next, I did:
# On the Beaglebone
cat /etc/hostname
And got:
# On the Beaglebone
I changed that with:
# On the Beaglebone
sudo nano /etc/hostname
# changed the hostname from arm to <new-hostname>
Finally I rebooted the Beaglebone to apply the changes.
# On the Beaglebone
sudo reboot

Change your login name

Now the terminal prompt says "ubuntu@beaglebone", the login is "ubuntu". I also changed that.

I had to enable the root account:
# On the Beaglebone
sudo passwd root
# Entered a temporary password
Pressed "Ctrl + D" to logout and I logged as root:

Logging as root.

I changed the old username with:
# On the Beaglebone
usermod -l <new-username> ubuntu
I also added a comment to my new user:
# On the Beaglebone
usermod -c "<full-name-or-comment>" <new-username>
Next, I moved to my new home:
# On the Beaglebone
usermod -md /home/<new-username> <new-username>
Finally, I also renamed the "ubuntu" group to match my new username:
# On the Beaglebone
groupmod -n <new-username> ubuntu
I logged out (Ctrl + D) and logged with my new username:

Logged with my new username.

Finally I locked the root account:
# On the Beaglebone
sudo passwd -l root

Set up a zeroconf hostname

A zeroconf hostname, simplifies SSHing with a local machine by assigning it a hostname on the LAN. This way I don't need to know the IP (which can change over time) to start a SSH session.
#On the Beaglebone
sudo apt-get install avahi-daemon
Now I can connect to the BeagleBone via ssh using the following command:
# On the PC
ssh <beagle-username>@<beagle-hostname>.local

SSHing the Beaglebone

I finished the screen session, using Ctrl+A and then K. I rebooted the Beaglebone, this way the avahi daemon got launched on the next boot.

ssh jorge@beaglebone.local instead of ssh jorge@192.168.1.x

SSH login without password

Everytime I SSH'ed the Beaglebone I needed to input the Beaglebone login and password. The next commands got rid of that.
# On the PC
ssh-keygen # Don't enter a passphrase
ssh-copy-id <beagle-username>@<beagle-hostname>.local

SSH without login

Install GNU screen

I quickly found out that I needed multiple SSH sessions to open multiple terminals on the Beaglebone. Searching for a workaround I found GNU Screen.

With GNU screen I can create multiple "screens", with one terminal inside each of them. All this can be done with keyboard commands.
#On the Beaglebone
sudo apt-get install screen
To start screen I needed to use the following command on every login.
#On the Beaglebone
screen -S 1
This was annoying, so I automated the task:
# On the PC
gedit ~/.bashrc
I appended the following text:
Now with a single command, I can SSH login into the Beaglebone and enter in a running "screen" or create a new "screen", if it doesn't exists.
#On the PC

SSH session with the Beaglebone splitted in 3 using screen.

Other important software

I also installed additional software:
#On the Beaglebone
sudo apt-get install man-db # Manuals
sudo apt-get install vim # Text editor
sudo apt-get install octave # Numerical package
sudo apt-get install build-essential # make, gcc, et al.

What's next?


Sunday, October 21, 2012

Ubuntu: How to add Eclipse to the Unity Launcher

A quick how to: Add Eclipse to the Unity Launcher. You can add any other application to the Unity Launcher using these steps.

All the Unity Launchers (e.g. evince, gedit, etc) are implemented as .desktop files. These files are stored in the folder /usr/share/applications/. The .desktop file contains the following information: where the icon is located, where the executable is located, the launcher name, and other secondary information like a comment about the launcher.

Make Eclipse accessible from the command line

All the commands accessible from the command line are stored in a "bin" folder. The folder destined to user binaries is located in /usr/bin.

Let's add the eclipse executable to /usr/bin using the following command.

sudo ln -s /path/to/eclipse/eclipse /usr/bin/

Now eclipse is accessible from the command line as the command eclipse.

Put the icon in the right place

All the icons associated to a Unity Launcher are stored in the /usr/share/pixmap folder. Let's place the eclipse icon in the right folder.

sudo cp /path/to/eclipse/icon.xpm /usr/share/pixmap/eclipse.xpm

Create the .desktop file

Finally, you'll need to create a new .desktop file for Eclipse. Proceed with the following command.

sudo gedit /usr/share/applications/eclipse.desktop

Insert the following text inside this new file.

Note 1: If you didn't add eclipse to /usr/bin, you'll have to use the full path in the Exec section, e.g. Exec=/path/to/eclipse/eclipse

Note 2: If you didn't place the eclipse icon under the /usr/share/pixmap folder, you'll have to use the full path in the Icon section, e.g. Icon=/path/to/eclipse/icon.xpm

This is the result.

Now, Eclipse is accessible from dash and the Unity Launcher.

Sunday, October 7, 2012

Windows: Installing qwt library

Qwt is a Qt based library that extends the Qt API with plotting capabilities.


 I'm assuming you have already installed MinGW (GCC compiler) and the Qt library, if you haven't then check this post.

Next you'll need to add the MinGW binaries to the PATH environment variable, if you haven't done so. If you don't know how to edit environment variables, check this post.

Append "C:\mingw\bin" (use the correct directory path) to the PATH variable.

Append "C:\Qt\4.8.3\bin" to the PATH variable.

Grab the latest qwt source (zip version) from here.

Unzip the zip file, go inside the qwt folder and open the qwtconfig.pri file with a text editor.

Comment (i.e. add a '#' character to the leftmost side) the following line:

QWT_CONFIG     += QwtDesigner

Save and close the .pri file.

Now open a command line window and type the following commands:

cd C:\path\to\downloaded\qwt
make install

Note: Instead of  "C:\path\to\downloaded\qwt" use the correct path like "C:\Users\Jorge\Downloads\qwt-6.0.1"

A new folder will be created in the C:\ drive named qwt-6.0.1 or similar.

The final step is updating the environment variables, if you don't know/remember how check this post.

Append "C:\qwt-6.0.1\include" to CPLUS_INCLUDE_PATH
Append "C:\qwt-6.0.1\lib" to LIBRARY_PATH

Note:  You won't be able to see the qwt widgets in Qt designer with these installation steps. I haven't figured out yet how to enable that.

How to use qwt

Create a new Qt project in Qt creator, and add to the .pro file the next line:

Linking qwt library

Next, you'll need the library header files, all of them start with "qwt_". Add them where necessary as shown in the next image:

Including qwt header files.

Simple test

Let's do a very simple test and see if everything has been installed correctly. In your mainwindow.cpp source file type the next code:

Simple test source code.

Then run it, and you should see the following output.

Simple test output.

Other Examples

For more elaborated examples check qSerialTerm and ImageQ.

 ImageQ in Windows. Histogram was plotted using QwtPlot.

Windows: Environment Variables for MinGW

Environment variables, as the name implies, are variables that hold directories paths as strings. Environment variables goal is to keep track of important files for the system.

In windows, the most important environment variable is the PATH variable. You can check its content on the command line using the following command:

echo %PATH%

Environment variables can also keep track of important files for the compiler (e.g. MinGW GCC) like header files and static and dynamic library files.

Adding, editing or deleting environment variables

To add, modify or delete an environment variable, you'll need to head to Control Panel > System > Advanced System Settings. On the Advanced tab, click on the Environment Variables... button.

The following window will pop out.

List of environment variables

Environment variables are divided in two groups: User variables and System variables. The most important group is the System group. You can create, modify or delete variables using the button New, Edit or Delete respectively.

Let's try editing the Path variable. Click on the Path variable in the System variables group and then click the Edit button.

As you can see, the variable is a list of directory paths separated by the ";" character. The most safe way of adding a new directory is by appending the path as follows:


That way there won't be name crashes.

There are many environment variables, let's review the most important ones.

Binary path (PATH)

The PATH (or Path, Windows is case insensitive) variable holds paths to binary files like .exe files, to commands and to .dll files.

Be careful with this variable, do not delete the default path like System32 and so on. Generally, you'll only need to append new directory paths to this variable.

For example:

Append ";C:\mingw\bin" to the Path variable

Important note: Do NOT create a new Path or PATH (again, Windows is case insensitive) variable in the system variable group or you'll override the default paths and you'll be in trouble.


These variable hold the directory paths to header files (like library header files). Important for linking new installed libraries.

Generally you'll need to append the path to a library "include" folder.

For example:

Append ";C:\mingw\include" to the CPLUS_INCLUDE_PATH

CPLUS_INCLUDE_PATH and C_INCLUDE_PATH are pretty much the same. When the compiler looks for a header file, it looks in both variables. So having two variables is only useful for the programmer to keep things tidy.

Library path (LIBRARY_PATH)

This variable hold the directory paths to static library (.lib or .a files). This one is also important for linking new libraries.

Generally you'll need to append the path to a library "lib" folder.

For example:

Append ";C:\mingw\lib" to the LIBRARY_PATH

Saturday, October 6, 2012

How to: OpenCV in Qt creator and ImageQ

In this post I'll cover how to glue the OpenCV libraries to Qt creator via an example. And I'll also release ImageQ, a Qt based image processing application.


OpenCV is an open source library that contains various functions for computer vision and image processing. OpenCV is written in C/C++ but there are ports for Java and Python.

Qt framework

Qt is a framework for cross development of Graphical User Interfaces (GUI) in C++. Qt libraries are open source.

Qt creator is an Integrated Development Environment (IDE) for Qt applications. Qt creator was created using the Qt framework as well.


You'll need the following libraries/software:

  • Qt creator
  • Qt libraries
  • OpenCV libraries


Open a linux terminal and type the following commands:

sudo apt-get install qtcreator # Qt creator + Qt libraries
sudo apt-get install libopencv-dev # OpenCV libraries

On Ubuntu 12.04 you'll end with Qt libraries version 4.8 and OpenCV libraries version 2.3.


First, you need Qt creator and Qt libraries. Follow the steps in this post and come back.

Now, grab and unzip OpenCV from here.

Next, install CMake (win32 exe) from here.

You'll need to add C:/mingw/bin to your PATH environment variable. Check this post for a how to.

Now, launch cmake-gui.

Select as source folder: The unzipped version of OpenCV and as build folder: any folder you want. Then click on the configure button, from the drop down menu select the MinGW makefiles and accept. You should get the following output.

OpenCV build configuration.

Go with the default configuration and click the generate button.

Now open a cmd and head to your "build folder" (the one you selected in CMake) and run the following command:


Now go get a coffee, a sandwich or take a nap while the compiler does it job.

(coffee break)

OK, after thousands of compiler messages, you finally obtained the necessary binaries.

Execute the next command:

mingw32-make install

A new folder name "install" will be created in your "build folder". Copy the contents of this "install" folder in any folder you like (e.g. C:/opencv). You can now delete the "source code folder" (the one you download from OpenCV website) and the intermediate compiled objects (a.k.a. your "build folder").

Now you'll need to modify some environment variables. Check this post if you don't know how.

I'm assuming you are using the C:\opencv folder, change the path if necessary.

Append to the PATH (or Path, is the same, do NOT create a new variable) variable: C:\opencv\bin

Append to the CPLUS_INCLUDE_PATH variable: C:\opencv\include

Append to the LIBRARY_PATH variable: C:\opencv\lib

Setting up the Qt project

(The rest of the article is the same for Ubuntu and Windows users)
  • Launch Qt creator.
  • Start a new project (usually Qt Gui Application).
  • Head to your .pro file.
  • Inside the .pro file add these lines:

Linking OpenCV libraries (Linux)

Note: You probably won't need to link all the libraries, only link the ones you are going to use. The most common libraries are core, highgui and imgproc.

Adding the headers

OpenCV library headers are inside the opencv2 folder. To add these headers to your application add the following line:

Adding OpenCV library headers.

Displaying the images

OpenCV offers a function named cv::imshow for displaying images. However this method won't integrate to your Qt application.

In Qt, images are usually displayed in QLabels using the method setPixmap(). As the name implies the argument for this method must be a QPixmap object. QPixmap objects are optimized for displaying, meanwhile QImage objects are optimized for pixel manipulation. Using the static method QPixmap::fromImage() a QImage can be converted in a QPixmap.

Is easier to convert a cv::Mat, the basic OpenCV image object, to a QImage object than to a QPixmap objetc.

In summary, the necessary steps are listed below:

  • Convert the cv::Mat object to a QImage object.
  • Convert the QImage object to a QPixmap object, using QPixmap::fromImage().
  • Add the QPixmap object to a QLabel, using setPixmap().

To convert a cv::Mat to a QImage, you can use my implementation available on the following links: header and source.

An example

Let's put everything together in an example. Head to your .ui file and add a label (leave the default name "label"), as shown in the following image. (I have also added grid layout, not necessary but helps visualization)

Toy application layout

Next, add the mat2qimage.cpp and mat2qimage.h to your project.

Now, on your mainwindow.cpp source file type the following code:

Toy application source code.

Note: In Windows, I had to use the full path to the image and the '\' characters needed to be written as "\\" insted. Example: "C:\\Users\\Jorge\\Desktop\\myimage.JPG".

This is the output, after running the example:

Toy example output. (Image from wikipedia)


Using these basics, I have developed ImageQ in Qt. ImageQ provides GUI access to some basic OpenCV functions. You can use ImageQ to learn the basics of image processing or to experiment with OpenCV function parameters.

ImageQ: Coin image after Sobel operator.

You can get ImageQ source code from this github repository.

P.S. For ImageQ you'll also need Qwt libraries, you can install these in Ubuntu using the following command. (Windows users, check this post instead)

sudo apt-get install libqwt-dev