ftt_treespp-class: S4 class for tree species: ID codes and keys to look up...
In mikemahoney218/blender-forthetrees: See the Forest (Using 3D Renders in Blender)

S4 class for tree species: ID codes and keys to look up rendering methods.

id_code: The code indicating what sort of identifier is stored in id_key – one of fia_code, plants_code, common_name, genus, or species.
id_key: The key identifying the tree species in the schema referenced by id_code.
idx: Character: a unique identifier (or "index") for each object to be modeled. Must be unique with no NA or NULL values, but otherwise is not validated.
x,y,z: Numeric: distance of the origin of the object from the origin of the grid system (the central point at 0, 0, 0) in meters in the given direction. Must have no NA, NULL, NaN, Inf, or -Inf values.
metadata: Data frame: a table containing additional information on the objects to be modeled. Optional, but if this slot is used then the data frame must contain a column named idx which should correspond to the idx slot. Only the existence of this column is validated.
appendix: List: additional data produced in the generation of the object. Not validated; any additional outputs that don't map to modeled objects may be inserted here.