How to use "PASCAL Annotation" files to train SVM with C++ - c++

Question

I need to test my selfwritten person detector using Hog Descriptor (Dalal paper) on a Scientific dataset (INRIA person dataset). I have thousands of pos and neg Images in my Folder to train a Support Vector Machine (SVM). However to label the Images as positive (1.0) or negative (-1.0) I need to read the information from a text file that is provided with the dataset in a so called "PASCAL Annotation" format.
My problem is that I don't know how to read this format efficiently. I'm using C++ and OpenCV. Does anyone know how to do this efficiently? Are there already code snippets for C++?
In the end I need a loop that goes through a file "Annotations.lst" where all the picture filenames are listed. The program loads the picture and the corresponding annotation file (picturename.txt) to see if this picture belongs to a positive or negative training data (or later when actually detecting: if the tested picture belongs to a detected person or not)
Thanks for your help!

Answer 1

Maybe it's not the best implementation but works fine, hope it becomes useful even today! You will need filesystem library in order to work with files.
string line,value; //Line stores lines of the file and value stores characters of the line
int i=0; //Iterate through lines
int j=0; //Iterate through characters
int n=0; //Iterate through ,()-...
char v; //Stores variable value as a char to be able to make comparisions easily
vector <Rect> anotations; //Stores rectangles for each image
vector <int> bbValues; //Bounding box values (xmin,ymin,xmax,ymax)
fs::path anotationsFolder = "THE FOLDER PATH OF ANOTATIONS"; //Path of anotations folder
fs::path anotationsParsedFolder = "THE FOLDER PATH TO STORE PARSED ANOTATIONS"; //Path to store new anotations
fs::recursive_directory_iterator it(anotationsFolder); //Iteradores of files
fs::recursive_directory_iterator endit;
cout<<"Loading anotations from "<<anotationsFolder<<endl;
while((it != endit)) //Until end of folder
{
if((fs::is_regular_file(*it))) //Good practice
{
fs::path imagePath(it->path()); //Complete path of the image
cout<<"Reading anotations from"<<it->path().filename()<<endl;
ifstream inputFile; //Declare input file with image path
inputFile.open(imagePath.string().data(), std::ios_base::in);
i=0;
while (! inputFile.eof() ){ //Until end of file
getline (inputFile,line);//Get lines one by one
if ((i>=17) && ((i-17)%7==0)){ //In lines numer 17,24,31,38...where bounding boxes coordinates are
j=69;
v=line[j]; //Start from character num 69 corresponding to first value of Xmin
while (j<line.size()){ //Until end of line
if (v=='(' || v==',' || v==')' || v==' ' || v=='-'){ //if true, push back acumulated value unless previous value wasn't a symbol also
if (n==0){
bbValues.push_back(stoi(value)); //stoi converts string in to integer ("567"->567)
value.clear();
}
n++;
}
else{
value+=v; //Append new number
n=0;//Reset in order to know that a number has been read
}
j++;
v=line[j];//Read next character
}
Rect rect(bbValues[0],bbValues[1],bbValues[2]-bbValues[0],bbValues[3]-bbValues[1]); //Build a rectangle rect(xmin,ymin,xmax-xmin,ymax-ymin)
anotations.push_back(rect);
bbValues.clear();
}
i++;//Next line
}
inputFile.close();
cout<<"Writing..."<<endl;
//Save the anotations to a file
ofstream outputFile; //Declare file
fs::path outputPath(anotationsParsedFolder / it->path().filename());// Complete path of the file
outputFile.open(outputPath.string().data(), ios_base::trunc);
// Store anotations as x y width heigth
for (int i=0; i<anotations.size(); i++){
outputFile<<anotations[i].x<<" ";
outputFile<<anotations[i].y<<" ";
outputFile<<anotations[i].width<<" ";
outputFile<<anotations[i].height<<endl;
}
anotations.clear();
outputFile.close();
}
++it;//Next file in anotations folder
}