Geometry of Stereo Vision explained

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In this video, I explain the geometry of stereo Vision. Please have look at my other tutorial about finding the essential and fundamental matrix.

The relation between the size of an object and its projection in camera fame

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What is the relation between the size of an object and its projection in camera fame? In this video, I explain how far you should stay from an object to see it at your desired size at camera frame

Vanishing points in computer vision explained

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In this tutorial, I explain the vanishing points in computer vision.

Equation of Line and Plane in 3D Space Explained

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The equation of Line and plane in 3D Space:

How to develop GUI Application with PyQt (python Qt)

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There are two main methods for developing GUI application with qt:
1) Adding all widgets in your code (your cpp or python code)
2) Creating qt UI files, adding widgets there and load everything into your application.

1)Adding all widgets in your code

Here is the snippet for adding all widgets and their slots in code:

import sys
print(sys.version)
import warnings
warnings.filterwarnings('ignore')


from PyQt5 import QtCore, QtWidgets
from PyQt5.QtWidgets import QMainWindow, QLabel, QSlider
from PyQt5.QtCore import QSize, Qt, pyqtSlot,pyqtSignal 



class HelloWindow(QMainWindow):
    
    pushButtonClicked = pyqtSignal()
    valueUpdating = pyqtSignal(int)
    
    
    def pushButtonClicked(self):
        self.title.setText("PyQt updated!")
            
    def valueUpdating(self, value):
        self.title.setText(str(value))
    
    def __init__(self):
        QMainWindow.__init__(self)

        self.setMinimumSize(QSize(640, 480))    
        self.setWindowTitle("Hello world") 

        self.title = QLabel("PyQt!", self)
        self.title.setAlignment(QtCore.Qt.AlignCenter) 


        self.pushButton = QtWidgets.QPushButton(self)
        self.pushButton.setGeometry(QtCore.QRect(140, 200, 99, 27))#x,y, width, height
        self.pushButton.setObjectName("pushButton")
        self.pushButton.setText("Click Me!")
        self.pushButton.clicked.connect(self.pushButtonClicked)
        
        self.slider = QtWidgets.QSlider(self)
        self.slider.setGeometry(QtCore.QRect(100, 20, 100, 30))
        self.slider.setFocusPolicy(Qt.StrongFocus)
        self.slider.setTickPosition(QSlider.TicksBothSides)
        self.slider.setSingleStep(1)
        self.slider.setPageStep(1)
        self.slider.setMaximum(100)
        self.slider.setMinimum(0)
        self.slider.setOrientation(Qt.Horizontal)
        
        self.slider.valueChanged.connect(self.valueUpdating)
        


if __name__ == "__main__":
    app = QtWidgets.QApplication(sys.argv)
    mainWin = HelloWindow()
    mainWin.show()
    sys.exit( app.exec_() )

import sys

print(sys.version)

import warnings

warnings.filterwarnings('ignore')

from PyQt5 import QtCore, QtWidgets

from PyQt5.QtWidgets import QMainWindow, QLabel, QSlider

from PyQt5.QtCore import QSize, Qt, pyqtSlot,pyqtSignal

class HelloWindow(QMainWindow):

pushButtonClicked = pyqtSignal()

valueUpdating = pyqtSignal(int)

def pushButtonClicked(self):

self.title.setText("PyQt updated!")

def valueUpdating(self, value):

self.title.setText(str(value))

def __init__(self):

QMainWindow.__init__(self)

self.setMinimumSize(QSize(640, 480))

self.setWindowTitle("Hello world")

self.title = QLabel("PyQt!", self)

self.title.setAlignment(QtCore.Qt.AlignCenter)

self.pushButton = QtWidgets.QPushButton(self)

self.pushButton.setGeometry(QtCore.QRect(140, 200, 99, 27))#x,y, width, height

self.pushButton.setObjectName("pushButton")

self.pushButton.setText("Click Me!")

self.pushButton.clicked.connect(self.pushButtonClicked)

self.slider = QtWidgets.QSlider(self)

self.slider.setGeometry(QtCore.QRect(100, 20, 100, 30))

self.slider.setFocusPolicy(Qt.StrongFocus)

self.slider.setTickPosition(QSlider.TicksBothSides)

self.slider.setSingleStep(1)

self.slider.setPageStep(1)

self.slider.setMaximum(100)

self.slider.setMinimum(0)

self.slider.setOrientation(Qt.Horizontal)

self.slider.valueChanged.connect(self.valueUpdating)

if __name__ == "__main__":

app = QtWidgets.QApplication(sys.argv)

mainWin = HelloWindow()

mainWin.show()

sys.exit( app.exec_() )

2) Creating qt UI files, adding widgets there and load everything into your application

Now let’s do what we have done in the first method in a UI file and load it. First, create a text file and put the followings in it and save it as “mainwindow.ui”

<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
 <class>MainWindow</class>
 <widget class="QMainWindow" name="MainWindow">
  <property name="geometry">
   <rect>
    <x>0</x>
    <y>0</y>
    <width>617</width>
    <height>419</height>
   </rect>
  </property>
  <property name="windowTitle">
   <string>MainWindow</string>
  </property>
  <widget class="QWidget" name="centralwidget">
   <widget class="QPushButton" name="pushButton">
    <property name="geometry">
     <rect>
      <x>200</x>
      <y>120</y>
      <width>99</width>
      <height>27</height>
     </rect>
    </property>
    <property name="text">
     <string>PushButton</string>
    </property>
   </widget>
   <widget class="QLabel" name="title">
    <property name="geometry">
     <rect>
      <x>60</x>
      <y>30</y>
      <width>67</width>
      <height>17</height>
     </rect>
    </property>
    <property name="text">
     <string>PyQt!</string>
    </property>
   </widget>
   <widget class="QSlider" name="slider">
    <property name="geometry">
     <rect>
      <x>190</x>
      <y>30</y>
      <width>160</width>
      <height>29</height>
     </rect>
    </property>
    <property name="orientation">
     <enum>Qt::Horizontal</enum>
    </property>
   </widget>
  </widget>
  <widget class="QMenuBar" name="menubar">
   <property name="geometry">
    <rect>
     <x>0</x>
     <y>0</y>
     <width>617</width>
     <height>25</height>
    </rect>
   </property>
  </widget>
  <widget class="QStatusBar" name="statusbar"/>
 </widget>
 <resources/>
 <connections/>
</ui>

<?xml version="1.0" encoding="UTF-8"?>

<class>MainWindow</class>

<rect>

</rect>

</property>

<string>MainWindow</string>

</property>

<rect>

</rect>

</property>

<string>PushButton</string>

</property>

</widget>

<rect>

</rect>

</property>

</property>

</widget>

<rect>

</rect>

</property>

<enum>Qt::Horizontal</enum>

</property>

</widget>

<rect>

</rect>

</property>

</widget>

</widget>

</ui>

Now call it in your python file like this:

import sys
print(sys.version)
import warnings
warnings.filterwarnings('ignore')


from PyQt5 import QtCore, QtWidgets
from PyQt5.QtWidgets import QMainWindow, QLabel, QSlider
from PyQt5.QtCore import QSize, Qt, pyqtSlot,pyqtSignal 
from PyQt5.uic import loadUi


class HelloWindow(QMainWindow):
    
    pushButtonClicked = pyqtSignal()
    valueUpdating = pyqtSignal(int)
    
    
    def pushButtonClicked(self):
        self.title.setText("PyQt updated!")
            
    def valueUpdating(self, value):
        self.title.setText(str(value))
    
    def __init__(self):
        QMainWindow.__init__(self)

        self.setMinimumSize(QSize(640, 480))    
        self.setWindowTitle("Hello world")
        loadUi('mainwindow.ui',self)
        self.pushButton.clicked.connect(self.pushButtonClicked)
        self.slider.valueChanged.connect(self.valueUpdating)

if __name__ == "__main__":
    app = QtWidgets.QApplication(sys.argv)
    mainWin = HelloWindow()
    mainWin.show()
    sys.exit( app.exec_() )

import sys

print(sys.version)

import warnings

warnings.filterwarnings('ignore')

from PyQt5 import QtCore, QtWidgets

from PyQt5.QtWidgets import QMainWindow, QLabel, QSlider

from PyQt5.QtCore import QSize, Qt, pyqtSlot,pyqtSignal

from PyQt5.uic import loadUi

class HelloWindow(QMainWindow):

pushButtonClicked = pyqtSignal()

valueUpdating = pyqtSignal(int)

def pushButtonClicked(self):

self.title.setText("PyQt updated!")

def valueUpdating(self, value):

self.title.setText(str(value))

def __init__(self):

QMainWindow.__init__(self)

self.setMinimumSize(QSize(640, 480))

self.setWindowTitle("Hello world")

loadUi('mainwindow.ui',self)

self.pushButton.clicked.connect(self.pushButtonClicked)

self.slider.valueChanged.connect(self.valueUpdating)

if __name__ == "__main__":

app = QtWidgets.QApplication(sys.argv)

mainWin = HelloWindow()

mainWin.show()

sys.exit( app.exec_() )

The results should be the same as what you got in the first method.

Adding Qt UI files to your CMake

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Qt uses qmake to generate classes from UI files and compile everything in the project, luckily there are some macros in CMake that allows you to bring everything into your CMake and build everything there, here is what you need to do:

cmake_minimum_required (VERSION 2.8.12)
project (Qt5CMake)

find_package (Qt5Widgets)

set (MyProjectLib_src ${PROJECT_SOURCE_DIR}/src/mainwindow.cpp)
set (MyProjectLib_hdr ${PROJECT_SOURCE_DIR}/include/mainwindow.h)
set (MyProjectLib_ui  ${PROJECT_SOURCE_DIR}/UI/mainwindow.ui)
set (MyProjectBin_src ${PROJECT_SOURCE_DIR}/src/main.cpp)

qt5_wrap_cpp(MyProjectLib_hdr_moc ${MyProjectLib_hdr})
qt5_wrap_ui (MyProjectLib_ui_moc  ${MyProjectLib_ui})

include_directories (${PROJECT_SOURCE_DIR})
include_directories (${PROJECT_BINARY_DIR})

add_library (MyProjectLib SHARED 
    ${MyProjectLib_src}
    ${MyProjectLib_hdr_moc}
    ${MyProjectLib_ui_moc}
)
target_link_libraries (MyProjectLib Qt5::Widgets)

add_executable(MyProject ${MyProjectBin_src})
target_link_libraries (MyProject MyProjectLib)

cmake_minimum_required (VERSION 2.8.12)

project (Qt5CMake)

find_package (Qt5Widgets)

set (MyProjectLib_src ${PROJECT_SOURCE_DIR}/src/mainwindow.cpp)

set (MyProjectLib_hdr ${PROJECT_SOURCE_DIR}/include/mainwindow.h)

set (MyProjectLib_ui ${PROJECT_SOURCE_DIR}/UI/mainwindow.ui)

set (MyProjectBin_src ${PROJECT_SOURCE_DIR}/src/main.cpp)

qt5_wrap_cpp(MyProjectLib_hdr_moc ${MyProjectLib_hdr})

qt5_wrap_ui (MyProjectLib_ui_moc ${MyProjectLib_ui})

include_directories (${PROJECT_SOURCE_DIR})

include_directories (${PROJECT_BINARY_DIR})

add_library (MyProjectLib SHARED

${MyProjectLib_src}

${MyProjectLib_hdr_moc}

${MyProjectLib_ui_moc}

)

target_link_libraries (MyProjectLib Qt5::Widgets)

add_executable(MyProject ${MyProjectBin_src})

target_link_libraries (MyProject MyProjectLib)

you can find the full project at my Github

Clang format and code beautifier for Qt Creator

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Different developers use different styles with different IDE (i.e some people use space, some use tab) which may cause lots of change in your git repository. One solution to this is to use some standard code formatting and beautifier. clang is a great tool for this purpose and can be easily integrated with git hooks and IDE.
First, install it by:

sudo apt-get install clang-format

1	sudo apt-get install clang-format

now if you have a file like this:

after running the following:

clang-format -style=WebKit -i main.cpp

1	clang-format -style=WebKit -i main.cpp

now you can use it like:

Available styles are LLVM, Google, Chromium, Mozilla, WebKit.

You can config clang for Qt Creator:

go to Tools>Option then:

And then go to the Environment>keyboard and set your shortcut:

This is what I get after pressing shift+s:

Every thing you need to know to master git, Part 7, git branch

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It quite often happens that a software product is on a git server and developers add new features to the product. To make the job easier, developers usually create branches beside the master branch (which is the default branch) and work on their branch and once the changes are confirmed and tested, they will be merged to the master branch. So let’s get started:

mkdir repos1
mkdir repos2
mkdir remote_repose

cd repos1
git init
git init --bare ../remote_repose/
git remote add origin ../remote_repose/

touch  A.txt
date >A.txt
git add -A
git commit -a -m 'A Added'
git push --set-upstream origin master
cd ../repos2
git clone ../remote_repose .

mkdir repos1

mkdir repos2

mkdir remote_repose

cd repos1

git init

git init --bare ../remote_repose/

git remote add origin ../remote_repose/

touch A.txt

date >A.txt

git add -A

git commit -a -m 'A Added'

git push --set-upstream origin master

cd ../repos2

git clone ../remote_repose .

ok now let’s create two branches, one for developer1 and one for developer2,

cd ../repos2
git branch b2
cd ../repos1
git branch b1

cd ../repos2

git branch b2

cd ../repos1

git branch b1

let’s make some work on the first branches:

cd ../repos1
git checkout b1
touch B.txt
git add -A
git commit -a -m 'B.txt Added in branch b1'
git push --set-upstream origin b1

date > A.txt
git add -A
git commit -a -m 'A.txt updated in branch b1'
git push --set-upstream origin b1

cd ../repos1

git checkout b1

touch B.txt

git add -A

git commit -a -m 'B.txt Added in branch b1'

git push --set-upstream origin b1

date > A.txt

git add -A

git commit -a -m 'A.txt updated in branch b1'

git push --set-upstream origin b1

and some changes in the second branch:

cd ../repos2
git checkout b2
touch C.txt
git add -A
git commit -a -m 'C.txt Added in branch b2'
git push --set-upstream origin b2

date > A.txt
git add -A
git commit -a -m 'A.txt updated in branch b2'
git push --set-upstream origin b2

cd ../repos2

git checkout b2

touch C.txt

git add -A

git commit -a -m 'C.txt Added in branch b2'

git push --set-upstream origin b2

date > A.txt

git add -A

git commit -a -m 'A.txt updated in branch b2'

git push --set-upstream origin b2

now you should see this in git gui or if you type:

git graph

git graph

Now in the git gui, go to merge>local merge and choose b1, you will get the following error because of the merge conflict:

so call the following to solve the conflict:

choose C and save and then:

git clean -i
git commit -m 'branch b1 merged into b2'
git push

git clean -i

git commit -m 'branch b1 merged into b2'

git push

Every thing you need to know to master git, Part 6, git stash

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Sometimes you have made some changes into your local copy and you don’t want to make a commit because your code doesn’t compile, but something came up and you should change your branch for instance and you will lose your local changes. In this situation, you can stash your changes and save your changes and change your branch for instance.

Let’s have a complete example:

mkdir repos1
mkdir repos2
mkdir remote_repose

cd repos1
git init
git init --bare ../remote_repose/

git remote add origin ../remote_repose/

touch A.txt
git add -A
git commit -a -m 'A.txt added'
git push --set-upstream origin master

touch B.txt
git add -A
git commit -a -m 'B.txt added'
git push --set-upstream origin master

mkdir repos1

mkdir repos2

mkdir remote_repose

cd repos1

git init

git init --bare ../remote_repose/

git remote add origin ../remote_repose/

touch A.txt

git add -A

git commit -a -m 'A.txt added'

git push --set-upstream origin master

touch B.txt

git add -A

git commit -a -m 'B.txt added'

git push --set-upstream origin master

now we make some change:

date > A.txt
ls > B.txt

1 2	date > A.txt ls > B.txt

now let’s stash changes:

git stash

git stash

we can list and drop changes by:

git stash list
git stash drop
git stash save <msg>
git stash list
git stash show -p <stashid>
git stash drop <stashid>
git stash drop
git stash pop

git stash list

git stash drop

git stash save <msg>

git stash list

git stash show -p <stashid>

git stash drop <stashid>

git stash drop

git stash pop

Every thing you need to know to master git, Part 5, git cherry-pick

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To illustrate what is cherry-pick let’s imagine the following situation: you and another developer start working on project, you will both make some changes, but after a while the other developer find a bug in the code and you are interested in to only apply that hot-fix without taking other changes from another developer, in this situation you should do a cherry pick, so let’s do it:

mkdir repos1
mkdir repos2
mkdir remote_repose

cd repos1
git init
git init --bare ../remote_repose/
git remote add origin ../remote_repose/

touch A.txt
date >> A.txt
git add -A
git commit -a -m 'A Added'
git push --set-upstream origin master

mkdir repos1

mkdir repos2

mkdir remote_repose

cd repos1

git init

git init --bare ../remote_repose/

git remote add origin ../remote_repose/

touch A.txt

date >> A.txt

git add -A

git commit -a -m 'A Added'

git push --set-upstream origin master

and you continue with something like:

touch B.txt
git add -A

1 2	touch B.txt git add -A

The other developer checks out the repository and will start working and make the second commit:

cd ../repos2/
git clone ../remote_repose/ .
touch C.txt
git add -A
git commit -m 'C added' git push

cd ../repos2/

git clone ../remote_repose/ .

touch C.txt

git add -A

git commit -m 'C added' git push

and in the third commit, he fixes the problem with A.txt so he would something like this:

echo "Bug in the code fixed, please hot patch me" > A.txt
git add -A
git commit -m 'Problem with A.txt fixed, please fix your local copy'
git push

echo "Bug in the code fixed, please hot patch me" > A.txt

git add -A

git commit -m 'Problem with A.txt fixed, please fix your local copy'

git push

And he may continue his work with another commit:

touch D.txt
git add -A
git commit -m 'D added'
git push

touch D.txt

git add -A

git commit -m 'D added'

git push

Now you are only interested in the third commit and you don’t want to add other files to your local copy so you have to cherry pick the third commit, so all you have to do is fetch all changes, find the corresponding SHA1 value for the third commit and apply the cherry pick.

cd ../repose1
git fetch
git cherry-pick 8f81bfa2bebb55583b7049b0a7f6926c27acd4b2

cd ../repose1

git fetch

git cherry-pick 8f81bfa2bebb55583b7049b0a7f6926c27acd4b2

And now the file A.txt in repose1 should be same as the file in repose2 while C.txt and D.txt are not added to repose1.