I. Distance measurement
1. Touch the point you want to know the distance to.
2. After moving one step, touch the first point and the point you want to know the length of.
3. A line connecting the two points is shown, and then the calculation proceeds. When the calculation is finished, the result screen is displayed.

** Step: The distance the camera moves after clicking the first point
The distance calculation result is calculated as a ratio to the Step, and the result is calculated by multiplying this ratio by the Step. In case of "Gps on", the step is calculated using Gps. When "Gps off", the Step is entered manually in millimeters.

** The error in the calculation is due to the error in the distance between the estimation of the essential matrix and the position of the camera. In the case of the essential matrix, we tried to reduce it as much as possible by repeating calculations several times. Errors due to camera position occur in the following routine. In this app, the positions of matching points are calculated after epipolar alignment of two screens taken by the camera. It is assumed that the camera position is shifted from the epipolar alignment process during the epipolar alignment process. It has been found empirically that this error occurs greatly when moving left and right. Therefore, it is recommended to move the camera forward or backward between the first and second scenes.

** Matching uses corner detection. Occasionally, there is a case where there is no matching, which is caused by the matching method, and it was found that when the stride length is greater than 1/20 times the distance (empirical), matching is not possible.

** In the case of stride length, about 1/100 to 1/20 times the measurement distance is the appropriate stride size. Below 1/100x, it is not easy to recognize the difference between the two scenes (because the pixel position difference is small). Of course, we tried to overcome it by calculating in units of sub-pixels, but this is about 2 to 5 times the resolution and precision improvement.

** The optimal display resolution is 1480x720, 1280x720.

II. Camera Calibration (Optional)
1. Click the button to save "Chessboard.pdf" to the download folder.
2. Print the Chessboard.pdf.
3. Prepare the Chessboard, click the Camera Calibration button to start calibration. Follow the on-screen instructions to rotate the Chessboard up, down, left and right.
4. When calibration is complete, the screen automatically switches.