Hi William, thanks for getting back to me. Post producion means fixing proplems or enhancing an image resulting from 3D output.
Generally Architectural Visualisation (ArchVis) is when you work from cad drawings from say an Architect. You have layouts, plan views and elevations but they may be 2d. Firstly we would use these 2D drawings to create a 3D model using Sketchup or 3D max etc These are 3D modelling prorams. You would build a 3D model in the computer. It is truly 3 D you can rotate it go inside it much like a computer game...........so now you have the the geometry it is a collection of 3D shapes that you have made into the shape of a house or apartment block etc. You have built the house, driveway roads. pathways landscaping etc this may include plants or trees. So you have now built the geometry. This geometry has spatial information. But it now needs materials. You apply Materials, brickwork. plaster, coloured paint, metal, grass etc to the surfaces of the model. So now you have geometry with materials. But that is just geometry with materials applied. Then it is usual to export that geometry with the applied materials into a render engine. A render engin is a program that for ease of explaination recognises the geometry and materials and you configure it to shoot vertual photons at the geometry and materials. These vertual photons are modified by the materials in different ways and the "photons' Bounce around as they do in the real world until they hit the camera where the results are recorded as an image. That is a render. You do not need to know very much of the physics of lighting and photons. It is dumbed down for use mere motrals into a user friendly render program. The results may have some issues, A prime example is if you look at my image of the waterfront render you will se the ocean surface is 3d waves reflecting the light as it would in the real world...............BUT............where the surface meets the yatch hull at the jetty it is flat. but it should not be flat it should actually be wavy (disturbed) like the ocean surface. I would or should fix that with a phioto manipulation program like Affinity Photo. This is post production. I may also wish to add people modify a shadow or creates highlight or contrast/ colour temperature, mist fog, god rays put in a better sky etc. Render engines may not be perfect and the imperfections are fixed of modified in post production. The3d renders have lots of tools, but an artifact or abboration may not be noticed antil after the render is finnished. Renders can take a lot of time so it is much easier to fix or inproved in post production rather than gouing back to the render changing some settings and waiting for a result.
That was long winded and a fairly generic explination but the best I can do