How much to scale the tree model compared to what is in the .spm file.
The default value of scaleFactor is 0.3048, the conversion ratio from feet to meters. By default, 1 unit in SpeedTree Modeler is 1 foot, while the most conventional measurement in Unity is 1 unit = 1 meter. Therefore we apply a default scaling at import time so that the size of the imported model matches the source model.