Photogrammetry #2

As I posted last week, I have decided to try my hand at Photogrammetry, it is the perfect blend of many of the things I am interested in: photography, drones, and computers.

My first attempt was a little dodgy, but I was using a set of pictures that were not taken specifically for the purpose. So yesterday I sent up my little drone and took 675 pictures doing 4 circuits of the church at different distances, a grid of pictures looking straight down, and a bunch of close-ups of various details of the building. I have realized that I have bitten off quite a ridiculous subject as my first project- most of the tutorials I have read suggest tackling your car, or a shed, or something small and simple rather than a 30,000 sq ft church complex surrounded by trees! But I like a challenge 😉

I am using an open-source app called Meshroom to do this, and the first thing you do is feed in your pictures so it can analyze them. The screenshots above are after my computer working away overnight- it uses the gps and altitude info embedded in the pictures to locate each one (each of the squares is a camera position where a picture was taken, and the wireframe pyramid attached to it is the angle it was looking at) and then it analyzes each picture to find points of reference that it can triangulate from multiple pictures (interesting aside- I took and fed in 675 pictures, and it decided that 9 were not useful for the project, so it used 666- of a church!).

Anyhow, once it has that info, you can set boundaries of the actual area you are interested in, and then it will build a wireframe model of it. This then has to be simplified to make the files a reasonable size (you can make it super detailed, but the file sizes are HUGE!), and then you have to let it go back through all the pictures to add what is called the “texture” to the model- this is where it cuts little sections out of all the pictures you took and assigns them to the triangles of the wireframe model (and there are over 1/2 a million in this simplified wireframe- the original before I processed it down had nearly 4 million!).

This whole process took nearly 24 hours of my Xeon and Nvidia powered computer with 128 GB of RAM running all its 12 cores at between 90-100%, but at the end I had a very nice model I could upload to Stetchfab:

You can use your mouse to rotate the model, right click to move it around, and use your mouse wheel to zoom in and out.

I still have a lot to learn- there are a few rough edges and odd glitches here and there (and the top of the steeple is missing for some reason), but I’m really happy with how this turned out for just my second attempt 🙂