CGI vs 3D rendering: what UK architects actually need
If you have ever been asked for "a CGI" by one person and "a 3D render" by another for the same scheme, you have been asked for the same thing. The words are used interchangeably. What actually changes the brief is not the name but the job the image has to do: help a client agree a design, support a planning application, or sell the finished building. This guide sets out the difference in plain terms and points to the UK guidance that decides what a planning image has to show.
The short answer: same thing, different words
CGI stands for computer generated imagery. A 3D rendering is an image produced from a 3D computer model. In architecture the two describe the same output: a still or animation made from a model of the proposal, with materials, lighting and context added.
So the useful question is not "CGI or rendering?" but three others:
What is the image for? Design review, planning or marketing.
How accurate does it need to be? Does anyone need to rely on it for position and scale, or is it there to explain an idea?
Who will judge it? A client, a planning officer, a design review panel or a buyer.
Three jobs a visual can do
Design development. Early on, a visual helps the client and the team agree the concept. The RIBA Plan of Work 2020 describes Stage 2 (Concept Design) as the stage where the Architectural Concept is prepared and iterated through regular design reviews with the client and other stakeholders, and where the client may seek pre-application planning advice. Visuals here can be quick and simple: massing, a few camera angles, materials still open.
Planning. The RIBA Plan of Work 2020 notes that planning applications are generally submitted at the end of Stage 3 (Spatial Coordination), so the information behind them is as coordinated as it can be. Planning images are judged on whether they represent the proposal fairly in its real context. This is where the UK guidance below applies.
Marketing. Images made to sell or let a finished building can be styled, lit for mood and framed for impact. That freedom is the point, and also why a marketing image should not be submitted as if it were a planning visual.
The same 3D model can serve all three. The camera, the method and the level of verification change.
What planning guidance actually asks for
Two documents set the vocabulary most UK planners and landscape consultants use.
Landscape Institute TGN 06/19: four visualisation types
The Landscape Institute's Technical Guidance Note 06/19, Visual Representation of Development Proposals (17 September 2019), defines four types:
Type 1, annotated viewpoint photograph. Shows the extent of the site within the view and annotates key features. The guidance calls it the most basic form.
Type 2, 3D wireline or model. Computer generated visuals, generally without a photographic context, suited to describing the development itself.
Type 3, photomontage or photowire. The type the guidance says will commonly be produced to accompany planning applications. It gives a reasonable level of locational and photographic accuracy, does not need verification data or a precise survey of camera locations, and is "not suitable for the most demanding and sensitive of contexts".
Type 4, photomontage or photowire (survey or scale verifiable). Uses equipment and processes that give quantifiable verification data, so the image can be checked for accuracy, as with industry standard AVRs or verified views. The guidance describes it as the highest level of accuracy and verifiability, for the most demanding situations.
London View Management Framework: AVR levels
The Mayor of London's London View Management Framework Supplementary Planning Guidance (March 2012) uses the term Accurate Visual Representation (AVR). It defines an AVR as a static or moving image that shows the location of a proposed development as accurately as possible, prepared following "a well-defined and verifiable procedure" so assessors can rely on it. Appendix C sets out a cumulative scale:
AVR level | What it shows |
|---|---|
AVR0 | Location and size of the proposal |
AVR1 | Location, size and degree of visibility |
AVR2 | As AVR1, plus a description of architectural form |
AVR3 | As AVR2, plus the use of materials |
The same appendix advises that assessors should only request AVRs of a type that show the properties that need to be assessed from a specific location. In other words, a fully rendered AVR3 is not automatically the right answer for every view.
How the two fit together
The AVR levels describe how much of the proposal is shown. The TGN 06/19 types describe how the image is produced and how far it can be verified. TGN 06/19 states that the AVR0 to AVR3 approaches can be applied to Type 3 and Type 4 visualisations. A fully rendered, photoreal image can therefore still be a Type 3 if it was not made with verifiable survey data and camera matching.
So what do you actually need?
A practical way to brief it:
Concept and client sign off: simple model views or quick renders. No verification needed.
Planning, most schemes: ask the planning officer or your landscape and heritage consultants which viewpoints matter and which TGN 06/19 type they expect. The guidance says Type 3 is the type commonly produced for planning applications.
Sensitive sites, protected views and London Plan views: expect Type 4 verified views, and agree the AVR level for each viewpoint before any modelling starts.
Marketing: brief for mood and audience, and keep these images separate from the planning set.
Agree the viewpoints, type and AVR level early, ideally at pre-application stage, so the model is built to the accuracy the views will need. If you are comparing studios for this work, our guide to architectural visualisation in the UK covers what to look for.
Sources
Landscape Institute, Technical Guidance Note 06/19: Visual Representation of Development Proposals, 17 September 2019.
Mayor of London, London View Management Framework SPG, March 2012, Appendix C: Accurate Visual Representations.
RIBA, Plan of Work 2020 Overview, 2020.
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