To view the 3D Visualisation, click View | 3D Visualisation. Alternatively, click the toolbar button illustrated with a green cube. This will bring up the 3D Visualisation window.
Loading geometry into the Visualisation will take a time proportional to the size of the model. For particularly large models this may take several seconds to initialise. Once it has been loaded in, this will not need to be repeated as long as the Visualisation window is open.
Very large models may use a significant proportion of system memory. For viewing large models it is recommended that your system has a reasonable amount of RAM (2GB) or a dedicated graphics card - graphics cards are of course much more efficient at handling this sort of thing.