## 2 A Review of Available Landscape Object Resources  
3D virtual environments can be created using a number of landscape objects, which can be viewed in different perspectives and dimensions. These perspectives and dimensions are measured from real world objects. Some objects are location specific (wind turbines), others are more spatially generic and can be found everywhere with little variation (houses). Surface objects are commonly divided into geo-specific (as actually exists at the location) and geo-typical (as can normally be found in the vicinity). This distinction was first articulated by [PERSON] _et al._[7]. [PERSON] _et al._[8] extended this distinction to four main classes of landscape objects (Figure 1):  
* Specific: such as an actual identifiable buildings or trees. For example, the iconic Eureka Tower in Melbourne;
* Typical: individually located objects which are of the correct species (e.g., _Eucalyptus_ _camaldulensis_ in the basalt plains north of Melbourne) or building style (e.g., \"a Victorian Terrace \" but do not represent each tree or house individually;
* Representative: similar to typical but not individually placed. May be scattered within a town or forest boundary;
* Generic: randomly located trees or buildings (e.g., house, shed, factory, block of flats) not specific or even necessarily typical to the location. Figure 1: Four classes of landscape objects: Specific–the Eureka Tower Melbourne; Typical–a Victorian terrace house; Representative–Eucalyptus camaldulensis tree species on basalt plains; Generic–a tree.’  
Typical and representative landscape elements vary with context. In the case of buildings the vernacular architecture changes from country to country, between city to rural areas and over time. As object libraries become populated with greater numbers of typical elements so the mapping on which the landscape simulation is based can become more detailed in its attributes. The same applies to vegetation, which has typical species within mapped bioregions or vegetation classes. Our initial focus was on objects appropriate for Victorian conditions. [PERSON] [9] identifies the elements of landscape visualisation as landform, vegetation, water, structures, animals and people. Landform and water form parts of the surface and do not require inputs from an object library. Their geometry is always specific while the textures applied to their surfaces could be any of specific, typical, representative or generic. With the increasing availability of high resolution satellite imagery the land form texture is most commonly specific. The other Ervin elements are therefore the subject of this development. In particular we worked with structures (primarily buildings) and vegetation. At this stage we have paid limited attention to animals and people (avatars), though we have captured some of these in the Landscape Object Library. Creating and storing these landscape objects with the attribute information (height, width, density of an object in a region-discussed in section 3.2) creates some practical challenges. It is not yet possible that each and every object which comprises the real world would be modelled and stored in a comprehensive attributed digital format. In recent years, some developments towards this aspirational goal have been discussed [10]. The Victorian Department of Primary Industries (DPI) and Department of Sustainability and Environment (DSE) with the University of Melbourne and Royal Melbourne Institute of Technology (RMIT) University, are not only developing a collection of 2D and 3D objects, but are also making these objects openly available to support the creation of 3D virtual environments for past, present and future Victorian landscapes [11]. Such a collection of objects is referred to as a 3D object library.