Could somebody explain what is the problem with electronic shutter for aerial photography ?
I've seen many critics related to GoPro's shutter system, but honestly, I don't understand how it can interfere with photogrammetry priciples.
Electronic shutter means the sensor reading is done line by line. So, even though at pixel level, exposure may be very short (1/1600), the whole photo takes a while to be read, as much as 1/25seconds... that's ages!
Lets say you fly at 10m/s (fast for a copter but rather slowish for a plane), a photo that takes 1/25 s starts to be exposed at a point P and capture is finished 40cm ahead. Each pixel is excited for short time so the photo may look sharp, but the geometry is compressed along flight path if sensor readout rolls upwards... but the case is actually worse because the flight path is not a perfect line nor the speed is constant, and aircraft vibrations cause geometry ripples... the result is that photogrammetry principles are basically destroyed.
I got pixel errors for reprojections bigger than 14 pix for some markers that look perfect! the ground control error is 16 centimeters while the GSD is 4 milimeters. That's a nonsense!
I did the very same flight project one month ago just before excavations, with the very same lens but with an Olympus EPM1. It gave 0.15 pixel, and 0.009 m for ground control error... pretty decent.
After the flight with the GM1, the archaeologycal findings were covered with geo-textile and filled with sand to prevent damage and unwanted "visitors" during this winter. This was done inmediately after the flight and having photos briefly checked at my order "OK, surveying done, start closing the site"... but actually the survey done is a crap and I can't heal it by no means.