The need to illustrate recent speaking engagements, has necessitated the revisiting a virtual model of the Roman timber rampart based on foundations found at Shields Road, Byker, which a real place in Newcastle.  In addition, live reaction to my work, provides an opportunity to reconsider and improve its subsequent presentation, and thus every question, comment or observation is important.
Since this particular technological approach, and in particular the underlying reverse engineering, has proved too advanced for a parochial academia, it is worth restating the fundamental methodical differences between CAD modelling and visualisation of the past.
Reverse engineering ramparts
Previous Work on this type of structure has been well documented on this site; my initial modelling is always on paper in the form of a technical drawing, although in this case, I also built a scale models using match wood. Since they are time consuming, I only build 3d computer models of structures to test and demonstrate ideas, once I have a clear objective in mind.
This post is illustrated with screen “snapshot” of a 3d computer model in SketchUp, the quality of which is related to my computer's screen resolution. I could also output moving images from the model, such as a walk through or a panning view.
Quite unlike modelling a building, the key conceptual idea is that it the spaces between the posts that give the structure its utility. The robbed post pits at Shields Road suggest a foundation of posts placed in pairs, around which a rampart constructed from horizontal timbers placed at 0˚/ 90˚ to the line of the structure with others placed at 60˚. This would produce a very strong and credible structure with a wide fighting platform. The plan of this structure is entirely consistent with scale of timber ram parts frequently mentioned in the writings of Caesar.
Computer modelling, while it has become much easier, is still labour intensive, so it is important to define the objectives and scope of your project at the beginning. This helps determine the structure of your model in terms of components and layer; each baulk of timber is a component, and can belong to a layer, a group of components that can be visually turned off and on.
Getting it wrong....
In most systems there is a practical limit to amount of information that can be displayed or rendered. While it is possible to store vast amounts of image data, to process and display a high level of detail is more complex especially if the image is ‘moving’.
We have noted an underlying conflict between the requirement for some degree of “realism” to convey a sense of materials and the need to ensure the observer is aware that this is technical diagram designed to convey understanding.
While “pictures” and “diagrams” both convey information, the former tends to interact on a more emotional level, while the latter is aimed at comprehension and rational engagement.
Each individual model, like any diagrammatic representation, has to be understood on its own terms and visual conventions; your house may have started off flat with a bluish tinge, but that is not how it ended up. You may buy a new build house based on a picture, and perhaps a plan, but the builder required a set of diagrams, to convey the precise technical information required.
While such observations are already out of date, the ability to build virtual models in photo-realistic detail threatens to blur this important distinction. For the house builder this is a sales tool which can visualise the house with red carpets and green walls, or vice versa. However, for the archaeologist a diagram should express real data, as distinct from a picture, which however artistic or realistic is a work of the imagination.
Computer models are clever diagrams.
This explains why it is this websites somewhat radical policy to add anachronistic spoilers to images, just in case the viewer imagines they are dealing with an artistic representation, a picture of the past - one of those fictionalised conceptions which is added to enhance and give weight to a peer reviewed text.
Archaeology is only credible if we are able to embrace the idea of doubt and close our eyes to the beguiling simplicity of a visual past.
 Caius Julius Caesar "De Bello Gallico" and Other Commentaries English translation by W. A. MacDevitt, introduction by Thomas De Quincey (1915) http://www.gutenberg.org/etext/10657