Question: How do you make your 3D models?

Josh Wolstenholme answered on 19 Jun 2020:

Good question! Usually when I want to make a model I first need to think of something that I need. I use them to create topographic elevation files so that I can run numerical models and look at things like flooding and sediment movement. In the past, I have used the 3D models to produce a birds eye view of a surface to look at stone and vegetation coverage.

First, depending on what I’m looking at, I’ll need to decide if I can use my handheld camera or the drone. I then take lots of photos of what I’m interested in that overlap and are at slightly different angles. I also need ground control – this is what allows me to scale the model correctly. Sometimes I’ll use what’s called a ‘local’ coordinate system which means I don’t need where the site is in the context of the real world, so I can use points that match up further down the line as long as I know the distance between the points. If I am interested in where it is, I’ll need to go to each of those points and use a GPS or differential GPS which is a cm accurate system.

After doing all of the field work, back in the office I’ll download my photos and import them into a software called Agisoft Metashape. I use the pro version, but there is a 30 day trial so you can do this at home! There are also lots of different types of software for this. I’ll start by ‘aligning’ the photos. This involves the computer looking at all of the pictures and determining if they overlap or not, and what points are likely the same. The process can take a while and produces a sparse point cloud – basically a collection of points that don’t look like much. After that has finished, I need to tell the computer where those ground control points are so it can scale the model later, this is very tedious, especially when you have lots of photos!

Once that is done, we can generate the dense cloud, this is the model that looks like what you want, and also takes a while. Finally we can generate a mesh or 3D object file that we can play with to create elevation, 3D print or do other cool stuff with. You can see an example of my model of a small river in Dalby Forest here: https://sketchfab.com/3d-models/dalby-forest-uav-survey-20191203-be64f2985a4747988b2549d62c012952