void buildCloud(SGPropertyNode *cloud_def_root, SGPropertyNode *box_def_root, const string& name, sgVec3 pos, SGCloudField *layer);
void buildLayer(int iLayer, const string& name, double alt, double coverage);
void buildCloud(SGPropertyNode *cloud_def_root, SGPropertyNode *box_def_root, const string& name, sgVec3 pos, SGCloudField *layer);
void buildLayer(int iLayer, const string& name, double alt, double coverage);