re that paper… Most of the field trials put fixed GCP markers in the field at the start of the season, but that probably doesn’t help you much, and you still have to get good GPS values for the markers.
These fancy GCP markers are a great tool to have… (I was trying to find the actual cost but I can only find packages of 10 which cost like $7K, ie almost as much as RTK) so maybe it isn’t a better option.
But re-reading your question… Is your main requirement that the measurements in your models be physically accurate (ie 1m in the model = 1m in the real world), or do you need to align the maps more accurately to the real world and have them be internally spatially accurate?
So if you need measurement accuracy, then I think the question is how accurate ODM is at evenly reproducing spatial accuracy within a given model and if there are factors that impact this internal spatial accuracy?
If you can reliably know that the model is internally accurate, then the issue would be making sure it is scaled to re-world sizes. If this is the case, then if you are on-site anyway, couldn’t you manually measure the size of some obvious objects in the scene so you can scale the output model to be accurate and then go from there?
You could start by flying your own house or similar places you have access to and see if measuring something simple in the scene would let you accurately scale the model.
Other ODM people might have more to say on the internal spatial accuracy within ODM models.