1. Format structure
F4D is composed of 1 header file, 3 folders for indoor data structure, 3 binary files for outdoor data structure and 4 image files for textures used in LOD 2~5. Different with LOD systems of other 3D graphics fields, LOD system of F4D has reverse LOD order. The lower number LOD a model has, the more detailed data it has. It is for, in future, supporting flexible LOD based on an idea that bigger buildings can be seen from further distance. The name of the folder which contains one F4D dataset is ‘F4D_[dataKey]’ where ‘dataKey’ is an unique key for an F4D dataset.