I've learned a lot from what others share online. I'll try to give back a little here...
October 24, 2018
Clearly, this is not a blog that you want to sit on the edge of your seat waiting for the next post, unless you like to perpetually sit on the edge of your seat. To follow up on the blurb from May 2, I have satisfied myself on a couple points about using drones for gathering 3D data. First, they require several integrated components to work well, and this in practice is actually a little hard to get. Maybe the wifi signal goes away or suffers intereference, the rotors get clogged with the season's fallen leaves, or the camera just can't adapt to lighting conditions--any and all of these can happen, and result in crappy 3D models, and a cranky operator. I've decided to simplify. With a pole. The camera sits on the pole. I move the pole. If I can get my smartphone to connect to the camera, I get a first person view on the phone, and trigger the camera. If wifi fails, I place the camera on a timer. The camera takes the photo. I move the camera. The camera...About the camera. I have purchased a Canon G9 with a 1 inch sensor, and I'm blown away by the resolving power. The low end drone image in May 2 post captures the first order relief in a scene. The G9 captures higher order (that is, smaller) features. I can't fly as high, but for the features I am targeting, a 7 m pole is actually overkill. And not expensive. If you're thinking of SfM, I'd suggest becoming friends with a pole and a camera with at least a 1 inch sensor. And a smartphone that can control the camera.
May 2, 2017
I have been exploring low-end aerial imagery from a very inexpensive drone as a data collection tool. Actually, I'm trying to build a comparative study of low to high end drones to find the lower limit on cost and model definition. I purchased an Elfie drone (JRC-37) for ~$40, and spent another $20 on batteries and spare motors, and another $20 or so soldering iron and jewelers tool kit for addressing tiny screws. Other drones waiting in the wings (for calm days and a more sure hand at driving a drone) are Parrot's Bebop (~$200), and DJI's Mavic Pro (~$1000).
The first tests are in. I flew Elfie via an app on my android phone (Nexus 5) around my backyard. Videos are streamed to the phone and recorded in the phone automatically. Google Photos uploads the videos from the phone to the cloud (behind the scenes when wifi is available, usually). From the cloud, I download the movie to my PC, and then use VLC to extract frames from the video (640 x 512 pixels per frame). These are then loaded into a structure from motion software (I use PhotoScan for this), and a 3D model results from the imagery. Here's my house. Not bad for a toy drone. I think one could measure the house dimensions to within several inches (10-20 cm or so).