metrics_lefsky function classifies empty voxels as "Oligophotic"

[huytrungth]

Hi @ptompalski ,

I tested the metrics_voxels function with an ALS plot using zmin = min(Z) and noticed a potential issue in the metrics_lefsky function, specifically in lines 31-37. It appears that empty voxels are being incorrectly classified as "Oligophotic," likely because some voxels have Zmax = NA.

[ptompalski]

thanks @huytrungth
I will investigate and get back to you!
P