opencv getPerspectiveTransform not working - c++

Question

so I am working on an assignment in which I have to classify road signs based on input images. So naturally I used the canny function, and findContours, followed by approxPolyPD in order to get the corners of the image that I will be transforming.
However for some reason, I keep getting an error when I attempt to use getPerspectiveTransform for the next step. Please help.
Error:
OpenCV Error: Assertion failed (0 <= i && i < (int)vv.size()) in getMat_, file /home/path_to_opencv/opencv/modules/core/src/matrix.cpp, line 1192
terminate called after throwing an instance of 'cv::Exception'
what(): /home/path_to_opencv/opencv/modules/core/src/matrix.cpp:1192: error: (-215) 0 <= i && i < (int)vv.size() in function getMat_
Aborted (core dumped)
Code used:
#include "opencv2/core/core.hpp"
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include "opencv2/calib3d/calib3d.hpp"
#include <iostream>
#include <stdio.h>
#include <stdlib.h>
#define WARPED_XSIZE 200
#define WARPED_YSIZE 300
using namespace cv;
using namespace std;
Mat src; Mat src_gray, warped_result; Mat dst;
Mat speed_80, speed_40;
int canny_thresh = 154;
#define VERY_LARGE_VALUE 100000
#define NO_MATCH 0
#define STOP_SIGN 1
#define SPEED_LIMIT_40_SIGN 2
#define SPEED_LIMIT_80_SIGN 3
RNG rng(12345);
/** #function main */
int main(int argc, char** argv)
{
int sign_recog_result = NO_MATCH;
speed_40 = imread("speed_40.bmp", 0);
speed_80 = imread("speed_80.bmp", 0);
// you run your program on these three examples (uncomment the two lines below)
//string sign_name = "stop4";
string sign_name = "speedsign12";
//string sign_name = "speedsign3";
//string sign_name = "speedsign4";
string final_sign_input_name = sign_name + ".jpg";
string final_sign_output_name = sign_name + "_result" + ".jpg";
/// Load source image and convert it to gray
src = imread(final_sign_input_name, 1);
/// Convert image to gray and blur it
cvtColor(src, src_gray, COLOR_BGR2GRAY);
blur(src_gray, src_gray, Size(3, 3));
warped_result = Mat(Size(WARPED_XSIZE, WARPED_YSIZE), src_gray.type());
// here you add the code to do the recognition, and set the variable
// sign_recog_result to one of STOP_SIGN, SPEED_LIMIT_40_SIGN, SPEED_LIMIT_80_SIGN, or NO_MATCH
// PART 1 of Assignment 2
Mat canny_output;
vector<vector<Point> > contours;
vector<Vec4i> hierarchy;
Canny(src_gray, canny_output, canny_thresh, canny_thresh*2, 3);
findContours(canny_output, contours, hierarchy, RETR_EXTERNAL, CHAIN_APPROX_NONE, Point(0, 0));
vector<vector<Point> > contours_poly(contours.size());
for (unsigned int i = 0; i < contours.size(); ++i) {
approxPolyDP(Mat(contours[i]), contours_poly[i], contours_poly[i].size()*.02, true);
}
// Part 2 of Assignment 2
vector<vector<Point> > transform_result(contours_poly.size());
warped_result = getPerspectiveTransform(contours_poly, transform_result);
warpPerspective(src, dst, warped_result, dst.size());
//imshow("input", src);
//imshow("output", dst);
/*
Mat drawing = Mat::zeros( canny_output.size(), CV_8UC3 );
for(unsigned int i = 0; i< contours_poly.size(); i++ ) {
Scalar color = Scalar( rng.uniform(0, 255), rng.uniform(0,255), rng.uniform(0,255) );
drawContours( drawing, contours_poly, i, color, 2, 8, hierarchy, 0, Point() );
}
// Show in a window
namedWindow( "Contours", CV_WINDOW_AUTOSIZE );
imshow( "Contours", drawing );
//*/
// Returning to the predetermined code.
string text;
if (sign_recog_result == SPEED_LIMIT_40_SIGN) text = "Speed 40";
else if (sign_recog_result == SPEED_LIMIT_80_SIGN) text = "Speed 80";
else if (sign_recog_result == STOP_SIGN) text = "Stop";
else if (sign_recog_result == NO_MATCH) text = "Fail";
int fontFace = FONT_HERSHEY_SCRIPT_SIMPLEX;
double fontScale = 2;
int thickness = 3;
cv::Point textOrg(10, 130);
cv::putText(src, text, textOrg, fontFace, fontScale, Scalar::all(255), thickness, 8);
/// Create Window
char* source_window = "Result";
namedWindow(source_window, WINDOW_AUTOSIZE);
imshow(source_window, src);
imwrite(final_sign_output_name, src);
waitKey(0);
return(0);
}