21. A computer program product for simulating a virtual environment having a virtual model, said computer program product comprising: a computer usable medium having computer usable program code embodied therewith, said computer usable program code comprising: a computer usable program code configured to: identify a user entering the virtual environment and user context in the virtual model; render an output of the virtual model using objects in the virtual model; locate, in associated user memory, previous versions of the objects in the virtual model; identify specified differences between the objects in the virtual model and the previous versions of the objects located in the user memory; and render a layer of the identified differences on the rendered output of the virtual model by modifying the objects in the virtual model based on user preference, wherein an identified difference is rendered differently than another identified difference according to the user preference and according to type of object.
21. A computer program product for simulating a virtual environment having a virtual model, said computer program product comprising: a computer usable medium having computer usable program code embodied therewith, said computer usable program code comprising: a computer usable program code configured to: identify a user entering the virtual environment and user context in the virtual model; render an output of the virtual model using objects in the virtual model; locate, in associated user memory, previous versions of the objects in the virtual model; identify specified differences between the objects in the virtual model and the previous versions of the objects located in the user memory; and render a layer of the identified differences on the rendered output of the virtual model by modifying the objects in the virtual model based on user preference, wherein an identified difference is rendered differently than another identified difference according to the user preference and according to type of object. 23. A computer program product according to claim 21 wherein said computer usable program code is further configured to identify a subset of previous versions of the objects located in the user memory according to the user context comprising objects within a particular range of the user, wherein subsequent steps in the method only consider objects identified in the subset.