Goal of the project is to develop a software pipeline to identify the lane boundaries in a video from a front-facing camera on a car.
Here's a link to output of this project.
Tools Used python (cv2) - OpenCV
Use camera calibration images and, test road images to develop the pipeline. Test the pipeline with project videos.
Pipeline is likely to fail if there is too much curving in the road which can be corrected by using higher order polynomial fits. It is also going to fail in the road conditions having more signs than lane lines i.e. (hov lanes, arrow directions ) in challenge video.
- Compute the camera calibration matrix and distortion coefficients given a set of chessboard images.
- Apply a distortion correction to raw images.
- Use color transforms, gradients, etc., to create a thresholded binary image.
- Apply a perspective transform to rectify binary image ("birds-eye view").
- Detect lane pixels and fit to find the lane boundary.
- Determine the curvature of the lane and vehicle position with respect to center.
- Warp the detected lane boundaries back onto the original image.
- Output visual display of the lane boundaries and numerical estimation of lane curvature and vehicle position.
The code for this step is contained in the 3rd code cell of the IPython notebook.
I start by preparing "object points", which will be the (x, y, z) coordinates of the chessboard corners in the world. Here I am assuming the chessboard is fixed on the (x, y) plane at z=0, such that the object points are the same for each calibration image. Thus, objp is just a replicated array of coordinates, and objpoints will be appended with a copy of it every time I successfully detect all chessboard corners in a test image. imgpoints will be appended with the (x, y) pixel position of each of the corners in the image plane with each successful chessboard detection.
I then used the output objpoints and imgpoints to compute the camera calibration and distortion coefficients using the cv2.calibrateCamera() function.
Using the coefficents from the camera calibration distortion correction is performed by using cv2.undistort() in the code cell 6. Here is the example for distortion corrected image.
Combination of color (H,S) and absolute sobel x thresholds are used to generate a binary image in the code cell 8. Here is the example on a test image.
The code for my perspective transform includes a function called unwarp_img(), which appears in code cell 10 of Iynb notebook. The unwarp_img() function takes as inputs an image (img), as well as source (src) and destination (dst) points and applies a perspective transform to get the birds eye view. I chose the hardcode the source and destination points in the following manner:
h,w = image.shape[:2]
#Define 4 source points (which takes shape of trapezoid)
src = np.float32([[170, h], [550, 480],[750, 480], [1200, h]])
# Define 4 destination points (which takes shape of rectangle)
dst = np.float32([[250, h], [250, 0], [1050, 0], [1050, h]])This resulted in the following source and destination points:
| Source | Destination |
|---|---|
| 170, 720 | 250, 720 |
| 550, 480 | 250, 0 |
| 1100, 480 | 1050, 0 |
| 1200, 720 | 1050, 720 |
I verified that my perspective transform was working as expected by drawing the src and dst points onto a test image and its warped counterpart to verify that the lines appear parallel in the warped image.
Applying histogram on the warped image gives the location of left and right lines, that information is used to define a search window to detect the location of left and right lane pixels. Using the coordinates of the pixels a second order polynomial fit is used to draw a smooth curve. Cell 12 has the code and example image is shown in the figure 4.
Radius of curvature is calculation and distance from center calculation is done in the code cell 15 with the help of lecture notes. Distance from the center is calculated as difference between the center of lane lines and center of the image.
The Pipeline is defined in the code cell 16 and it is tested with test image 6 in code cell 17. Result for the pipeline is shown in the figure 5
