LOD Group的显示百分比，计算方法为
LodPercentage = 物件包围盒的高度 / 当前屏幕的高度
然后用LodPercentage，在配置中进行匹配

Percentage: As the object’s screen height goes from the current LOD height percentage to next, the blend factor goes from 1 to 0. Only the meshes of the current LOD will be rendered. Cross-fade: You need to specify a Transition Width value to define a cross-fading zone at the end of the current LOD where it will to transit to the next LOD. In the transition zone, both LOD levels will be rendered. The blend factor goes from 1 to 0 for the current LOD and 0 to 1 for the next LOD.The blend factor is accessed as the unity_LODFade.x uniform variable in your shader program. Either keyword LOD_FADE_PERCENTAGE or LOD_FADE_CROSSFADE will be chosen for objects rendered with LOD fading.

当包围盒的高度低于50%时，切成了LOD1