In Android version 6.0 or lower, you need to set permissions such as location and camera in the application settings of the mobile phone after the first installation.

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 visible, and then the calculation is carried out, and when the calculation is finished, the result screen is displayed.

** 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 of not being able to match. This is caused by the matching method, and it was found that when the stride length is greater than 1/20 times the distance (empirical), the matching is not possible.

** In the case of stride length, about 1/100 to 1/20 times the measurement distance is the proper size of the stride. 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.