`cyl` specification in OBJ format?

[han16nah]

Problem With the standard OBJ specification, modelling tree objects, whose woody structure can be approximated by cylinders, requires many triangle faces, depending on the level of detail, with which the cylinders should be approximated.

Possible solution An easier way could be the definition of cylinders, as done in the librat model. Example:

g object_name # define an object named "object_name" 
usemtl stem     # using material stem 
v 0 0 0              # the I vector defining the intersection 
v 0 10000 0      # the N vector defining the direction 
cyl -1 -2 5000   # a cylinder object with circumference 5000 units 

(https://github.com/philwilkes/librat_in_jupyter/blob/master/1.3_adding_objects_to_the_scene.ipynb)

We should think about if it would be feasible and beneficial to implement such a format. This also depends on how typical this format is and how easy it is to convert to/from.

Such a format is used in the original Wytham Woods 3D forest scene data publication (https://bitbucket.org/tree_research/wytham_woods_3d_model/src/master/stems/) as Calders et al. 2018 used it with the librat radiative transfer model.