Cylinder fitting (measuring DBH) for tropical forest plots
We have been trying to work with the cylinder fitting function of computree for quite some time for the purpose of automatically estimating DBH. The problem is that the cylinders never fit the true shape of the tree especially if it is has irregular shapes/leaning or so. We performed the function on individually extracted trees but it still fail to recognize the structure of the trees.. instead we got several cylinders that deviated from the tree and hanging on air.
If anyone already overcome these issues please share your experiences. Is there a certain parameter to be set or a step to follow other than the one on the HT5_Measuring_DBH_automatically.xsct2 step?
Note: our plots are in tropical cloud forest.
Thanks in advance!
RE: Cylinder fitting (measuring DBH) for tropical forest plots - Added by Hackenberg Jan over 2 years ago
” the cylinders never fit the true shape of the tree especially if it is has irregular shapes/leaning”.
Two different problems named here. Leaning tree is problematic for all cylinder fitting methods which have as a validation to catch wrong fits a good agreement between the cylinder axis and the z-axis. Alexandre has I think such validation in his DBH step - ONF plugin. You can try out if you want the SimpleTree solution given here: http://rdinnovation.onf.fr/boards/1/topics/912
The big problem is though irregular shape. I also worked with butress tropical trees and the SimpleTree cylinder fitting method is expected to perform worse here in disrespect to the first problem. MLESAC relies on RANSAC which is in this case less reliable than Gauss Newton methods. I know from a bit deeper state in the art that people do not recommend fitting circular structures at all. You need to research though on your own what might be prefarable. That one I refound quite easily as I know some of the authors better fast for starters:
Nölke N, L Fehrmann, I N Surati Jaya, T Tiryana, D Seidel and C Kleinn. 2015. On the geometry and allometry of big-buttressed trees - a challenge for forest monitoring: new insights from 3D-modeling with terrestrial laser scanning. iForest - Biogeosciences and Forestry, 8: 574-581. DOI: 10.3832/ifor1449-007.