Thanks for your reply Meta4. I had a chimney sweep ask me if there was a way to get measurements of a chimney with a drone for doing inspections, since some of the chimneys are quite high and on steep roofs. I started playing with it and if you know some of the parameters for the picture like the focal length, distance of the subject, and resolution, you can determine the size of a pixel and then measure the number of pixels to get the measurement. I was using the DJI Go app and the distance it gives on the screen from the collision avoidance system, but I don't think that is real accurate, since it will jump from 12 to 15 to 20 and back and forth. I saw the subject distance in the details of the file and thought if there was a way to turn it on, that would work great. I guess there isn't. Any other suggestions on how I might get a good distance for the calculations? Thanks.