Are there any good resources on getting started with estimated object dimensions? Similar to the measurable app but to do height and width.
I recommend checking out our documentation of our SceneGeometry API that we presented in ARKit 3.5. A good overview is given in this tech talk:
Advanced Scene Understanding in AR
After getting a geometry that is good enough you still have to solve the task of isolating your object of choice and computing its volume. There would be several ways of doing it. For example cutting everything off above the ground level, or letting the user create a cube objects and then intersect it with the scene geometry, we do not have any code sample for these tasks, though.