XO3D Studio · Technical guide
CAD to CGI.
CAD describes how a product is made. CGI has to describe how it looks and feels, to someone deciding whether to buy it. Those are different jobs, and the gap between them is where most technical product visualisation goes wrong. This is what actually transfers, what breaks on the way, and what your engineering team should send.
The studio behind this guide
When the CAD pipeline is our work
XO3D builds production CGI directly from client CAD, and the supplied geometry is reviewed before the model is scoped. Come to us when the source data is real engineering geometry and dimensional accuracy has to survive into the finished frame. One limit worth stating up front: a model built from your CAD is not an engineering sign-off and cannot certify a tolerance.
How XO3D compares to the other five supplier modelsIn short
What CAD to
CGI does.
CAD to CGI prepares engineering geometry, materials and scene structure for the camera and the output a project needs. CGI then does for a product what a photoshoot would, producing images and film, without needing a physical sample.
For the wider terms, see what CGI means in our glossary, or what product CGI covers. The table below is the short version of this guide: the five source issues that most often change the work, and what to confirm before modelling starts.
| Source issue | Why it matters to the image | What to confirm |
|---|---|---|
| Curved surfaces | CAD curves become polygons for rendering. Too coarse and a close-up shows facets. | Which shots are close-ups, so detail goes where the camera looks. |
| Assembly relationships | Anything that moves, opens or separates needs its own part in the hierarchy. | What moves in the film, and whether the export kept the parts separate. |
| Appearance references | CAD colours are for reading the model, not for the finished look. | The real finishes, from specifications, photographs or a physical sample. |
| Hidden parts | Internal parts slow every frame, but removing the wrong one can show through a gap. | Which views the shot list needs, so simplification follows the camera. |
| Design revision | A render of the wrong revision can still look convincing. | Which file is the current revision, and who can say so. |
CAD rendering or CAD to CGI?
A render made inside CAD software is a quick way to see a design. It uses the engineering model as it stands, with its own materials and lighting. CAD to CGI is a different job: the geometry, materials, lighting and camera are prepared as a production scene for a specific film or set of stills. This guide is about that second job.
Formats
What we
work from.
If your format is not listed, ask. Most engineering formats are workable, and the honest answer about yours takes one look rather than a meeting.
What survives depends on the export
Treat the notes in the table as starting points to check, not guarantees. Which 3D file format you send matters, but so do the export settings, whether referenced part files travel with an assembly, and what the importing software supports. Send a sample early and include every part the assembly depends on. With the files, note the units, the source revision and the export settings used, so the studio can tell a missing part from a deliberate omission. For format details, Check format options on XO3D Labs.
| Format | Software | Notes |
|---|---|---|
| STEP (.stp, .step) | Universal CAD interchange | Preferred starting point. Usually carries the geometry and assembly structure, depending on the export settings; check a sample. |
| IGES (.igs, .iges) | Universal CAD interchange | Common alternative to STEP. Workable in most production pipelines. |
| SolidWorks (.sldprt, .sldasm) | SolidWorks | Native files can keep more of the assembly hierarchy and appearance settings, if every referenced part file is sent with the assembly. |
| Rhino (.3dm) | Rhinoceros | Common in industrial and product design. Direct import. |
| Inventor (.ipt, .iam) | Autodesk Inventor | Native engineering files for mechanism and assembly work. |
| OBJ, FBX, 3MF | Generic 3D formats | Workable as a fallback when CAD source is not available. |
Five real problems
Where the
pipeline breaks.
None of these is a reason not to work from CAD. All of them are reasons to know about them before the model is built rather than after the first review.
Exact surfaces have to become polygons
CAD describes a curve as mathematics. A renderer needs triangles. That conversion, tessellation, is where a beautifully engineered fillet turns into visible faceting on a hero close-up. It is a production decision rather than an import setting, and it has to be made per part, at the resolution the final shot needs.
Assembly structure gets flattened
Exported CAD often arrives as one merged object. If the brief involves a mechanism opening, a part separating or an exploded view, that hierarchy has to be rebuilt before anything can move. Native files and a well-structured STEP export preserve far more of it, which is why the format you send matters.
CAD carries no usable appearance data
Engineering colour assignments are for reading the model, not for photography. Materials are developed from the available photographs, specifications and physical samples where supplied: the actual finish, the grain direction, the anodising, the soft-touch coating, how the paint behaves at a grazing angle. This is the largest single difference between a render that reads as real and one that reads as CAD.
Everything is in there, including what nobody sees
A production assembly contains fasteners, brackets and internal components that will never be visible. Left in, they slow every frame for no benefit. Taken out carelessly, something shows through a gap in a shot nobody anticipated. Deciding what to keep is part of the build.
Concept-stage geometry keeps moving
For a product still in development, the CAD you send is not the CAD that ships. That is normal and it is workable, but it means the 3D build has to be version-controlled alongside engineering rather than treated as a one-time handover. Fundamental changes to a mechanism are a scope conversation, not a silent absorption.
Three more things a source review may find
Not every CAD model has these problems. They are worth checking because each one is quicker to deal with before the model is built.
Referenced parts go missing
A native assembly often points to separate part files. If only the assembly file is sent, those parts can arrive empty or not at all. Send the full folder of dependent files, or a STEP export made from the complete assembly, and say if any parts were left out on purpose.
Surfaces are not ready for textures
Labels, printed artwork and directional finishes such as brushed grain need surfaces prepared to take a texture. Engineering geometry is not built for that, so a source review may find surfaces that need UV preparation before artwork can sit on them correctly.
The scene is heavier than the shots need
Thousands of separate objects with engineering names make a scene slow to work with and hard to animate. A source review may find parts to combine or rename. The shot list and the moving parts decide what can be simplified, so nothing that has to move or be seen up close gets merged away.
For more technical depth from a practitioner's side, Digital Production published an article on what goes wrong between engineering data and CGI.
Quality check
Check the model
at the intended
camera distance.
A curve in CAD is exact. For rendering it becomes a set of flat polygons, and how many polygons it gets is a judgement about the shot. A curve built coarsely can look perfectly smooth on a part in the background, and visibly faceted when the same part fills the frame in a close-up.
The opposite mistake costs time rather than quality. Geometry far denser than any shot needs makes the scene slower to open, animate and render, for no visible gain. So the useful question is not "how fine is the mesh?" but "how close does the camera get to this part?"
That is why the shot list matters to the model. Name the close-ups and the parts they feature, and the detail can go where the camera looks. Parts that only appear at a distance, or never appear, can be lighter.
Worked example
From evolving
Petalite CAD to a
reviewed product film.
Petalite's EV charging system is a published XO3D project where the problems in this guide came up in real production. The charger was still being developed while the films and stills were made.
The case records the CAD clean-up step by step. Petalite's CAD was taken into production and rebuilt: topology was repaired, overlapping geometry was resolved, the model was set to real-world scale, and a clear naming and grouping system was set up. That structure is what kept the project stable as the design changed, and kept every component consistent across the stills, turntables and animation.
The design did keep changing. The case notes that assets were updated regularly to reflect the latest engineering iterations. This is the revision problem described above: the model had to follow engineering rather than being a one-time handover.
Cable movement was the other hard part. There was little visual reference for how the cables should behave, so every cable beat was reviewed with the client in greycard, an untextured grey render, before final lighting. Those passes were used to agree sag, weight, bend radius and contact while changes were still quick to make.
As everywhere in this guide, a model reviewed with the client is a visual representation, not an engineering validation. See the Petalite project.
The gate that matters
Engineering
reviews the
model first.
Before any material, light or camera is added, your engineering team reviews the 3D model. Nothing else in the process protects a technical project as effectively, and skipping it is how a beautiful render of the wrong revision reaches a launch page.
What that review catches is specific: the wrong product version, an assembly relationship that does not reflect the real mechanism, a component at the wrong scale, geometry simplified somewhere it carries meaning. All of those are quick to fix at model stage and slow to fix once lighting, animation and multiple formats are built on top. The same review matters most for exploded views built from a CAD assembly, where every part is seen close up. For how a CAD model differs from the visual model and a digital twin, see digital model versus CAD model.
It needs one named person who can say yes. A review circulated to a group without an owner tends to come back as silence, which is the most expensive answer available.
On why the model has to be right
On a lot of the product launches we work on at XO3D, the CAD has to be accurate to the millimetre, and the product has to be represented exactly as it is.
Be precise about this
What accurate
does and does
not mean.
A model built from your CAD and confirmed by your engineers is a strong basis for a technically credible image. It supports a claim that the visual reflects the product as designed and as reviewed.
It is not a validation of the manufactured product, it is not an engineering sign-off, and it is not a regulatory approval. A render cannot certify a tolerance and should never be presented as though it does.
Where a specific accuracy or representational requirement exists, particularly on medical, industrial or safety-related products, define it at brief stage and name who approves it. That is a short conversation before production and a serious problem afterwards.
Edges are a simple example of the gap between an engineering model and the physical product. Thomas Howcroft, Founder and Creative Director, on what CAD leaves out:
In a CAD file the edges will be very sharp, like perfectly sharp, like a knife edge. But in real life you will never get the plastic to go into the edges like that. So you always get a nice filleted edge on almost all materials because there's never a 100% edge, or a perfect edge, no matter what material you use.
Before you send anything
The five things
worth gathering.
- The best CAD you have, in the best format you have
- STEP is the safest default. Native SolidWorks, Rhino or Inventor files preserve more. If the geometry is at concept stage, send it anyway and say so.
- Material and finish specifications
- Not colour names. The actual finish: anodised, powder-coated, soft-touch, brushed, and in which direction. Physical samples are better than any document.
- Engineering drawings where they exist
- Dimensions, tolerances and assembly relationships resolve ambiguity in the model far faster than a conversation about it.
- The mechanism sequence, if something moves
- What moves, in what order, and how far. A short video of a prototype, however rough, is worth more than a description.
- A named technical reviewer
- One person on your engineering side who can confirm the model is right before materials and lighting are built on top of it. This is the single most valuable thing you can supply.
Confidentiality comes first if the product is unreleased. How CAD is handled, who can open it and how long it is kept is set out on trust and security.
Handover
Record each
source before
it is used.
When CAD, photographs, a prototype and a specification all arrive together, they rarely agree on every detail. A short record for each source makes the disagreements visible before they reach a render. These six fields are a suggested format, not a form that ships with a project; leave a field blank if you do not know the answer yet.
- File and revision
- The file name and the revision or date it represents.
- What it is authoritative for
- Geometry, dimensions, finish, colour or artwork. One source rarely covers all of them.
- Date supplied
- When it reached the studio, so later files are easy to spot.
- Known changes
- Anything already known to differ from the production version.
- Unresolved detail
- Where this source disagrees with another one, and what is still open.
- Technical reviewer
- The named person who can settle a disagreement for this source.
Prepare the handover with the XO3D Labs asset preparation tools.
Check which product revision the reference actually shows
Connor describes projects where the supplied CAD and later product reference did not agree. He also describes a physical prototype whose materials and finish were not representative of the final product. A reference can be useful and still be the wrong authority for a particular detail.
Label the revision and purpose of each source: geometry, dimensions, finish, colour or artwork. Photograph the sides that are easy to miss, supply original logo and label artwork, and identify the person who can resolve a disagreement between the model, photographs and specification.
When sources conflict, confirm the intended production version before approving the model or material test. Keep the unresolved detail visible in the review notes. A convincing render cannot establish which manufacturing revision is correct.
From a production discussion, edited for clarity.
Past production insight from
Jack Robertson
Former Mid-Level Artist, XO3D
CAD can be missing the small parts, or carry far too much of them
Jack described supplied CAD as a mixed bag. Some models are missing minor details that an exploded shot depends on, such as screws and fasteners. Others include every small part, with very heavy mesh. Where parts are missing, the team fills the gap from a library of standard parts such as screws and nuts, or XO3D's modellers build the specific part from scratch.
On the G-Lab Keyz Hydrogen keyboard, the CAD lacked much of the internal detail. The team modelled parts such as the membrane and the button pads so the keyboard looked realistic in the exploded shots of the film.
In his words, a finished XO3D model contains correctly named parts, a named hierarchy with subgroups and the correct pivots. "The main thing it will include is a bespoke UV unwrap, to ensure that all textures, artworks and decals can be correctly applied."
From a production discussion while Jack worked at XO3D, edited for clarity. XO3D's named expert on this subject is Thomas Howcroft, Founder and Creative Director.
Related
Where to
go next.
Common questions
Technical
answers.
What CAD format should we send for CGI?
STEP is the safest default. It usually carries the geometry and assembly structure, but what survives depends on the export settings, so send a sample early. Native SolidWorks, Rhino or Inventor files can keep more of the hierarchy and appearance settings when every referenced part file is included. IGES is a workable alternative. OBJ, FBX and 3MF can be used as a fallback where no CAD source exists, though they arrive with less structure to work from. If your format is not listed, a source review will show what is usable.
Can you work from CAD that is not finished?
Yes, and much of the most useful work happens exactly there. For a product still in development the 3D build is version-controlled alongside engineering, so design changes can be brought in as they happen. Minor revisions such as a material change or a component adjustment are usually absorbed efficiently. A fundamental mechanism change is a revised scope conversation, and we raise that at the time rather than at delivery.
Does CGI from CAD mean the render is dimensionally accurate?
It means the visual model is built from your supplied CAD and reviewed by your engineering team before production continues. That is a strong basis for a technically credible image. It is not a validation of the manufactured product, and it is not a substitute for engineering or regulatory approval. Where a claim depends on accuracy, define the requirement at brief stage and name who signs it off.
Why do materials have to be rebuilt if the CAD already has colours?
Because CAD appearance data exists to help engineers read the model, not to survive a camera. A real finish behaves in ways a colour assignment cannot describe: how anodising shifts at a grazing angle, how a soft-touch coating scatters light, which way a brushed grain runs. Materials are developed from the available product references, and that reconstruction is most of the difference between a render that reads as a product and one that reads as CAD.
What if our CAD is enormous?
Large assemblies are normal for industrial and engineered products. The work is deciding what is visible in the shots the brief actually needs, retaining the geometry that carries detail at close range, and simplifying what will never be seen. Send the full assembly rather than a guess at what matters, and that decision gets made against the shot list.
Start with the files
Send us what
you have.
Tell us the format, the stage the design is at, and what the visuals have to do. We will tell you what is workable and what is missing.
Send us your CAD questionsYour next project
Start with the product source.
CAD is a starting point, not a finished campaign asset. Identify the current revision, visible components and material references before setting cameras or approving a production schedule.
A route to consider
Master Asset Build
One product built to production standard, with materials, lighting and a directed hero deliverable. Further uses are scoped around that foundation.
Bring these three things.
- Which CAD revision is approved?
- Which parts or finishes are still changing?
- Who can review the product model?
Start with an outline. We review the product, intended outputs and timing before agreeing the production scope.