Introduction:
In the intricate world of 3D rendering, 3D model preparation stands as the unsung hero, ensuring visuals come to life in the most captivating way. Delving into the nuances of this crucial step can transform an average render into a masterpiece. In this blog, we’ll unravel the key practices to perfect your 3D model preparation and take your renders to unparalleled heights.
Creating your models using CAD or Polygonal Modelling: What’s the difference?
3D models are digital representations of real-world objects. This digital copy can be calculated and built in many ways and is often created differently for the various use case requirements. Models made using CAD are most often developed for manufacturing and utilise a parametric modelling process in which the model’s geometry is defined and controlled by dimensions.
What is a Polygon?
In 3D modelling, a polygon is a flat, two-dimensional shape defined by a closed loop of vertices connected by edges. Polygons serve as the building blocks that make up the surface of 3D models. The most commonly used types of polygons in 3D modelling are triangles (triangular polygons with three sides) and quadrilaterals (four-sided polygons), though polygons with more sides can also be used. The faces, or polygons, are filled in to create the surface that gives the model its appearance when rendered. In 3D graphics, polygons are often used to approximate the surface of more complex shapes, allowing them to be rendered efficiently by a computer.
CAD modelling
This is often the more precise method that will generate the most accurate models, but the user’s control over the mesh is limited which can make life difficult when importing in 3D rending packages.
Polygonal modelling
This is a little different. These models are typically formed as a collection of vertexes and tri’s or quad meshes (and sometimes more) that we call faces or polygons.
A quad mesh would have a collection of four-sided faces with a vertex at each point of intersection.
A tri-mesh would be largely similar to this but would have each face split once further diagonally from one corner effectively turning each quad into 2 triangles.
Again, all three points on each triangle would intersect others and each of these points are called vertices. Models created in this method will often not have the dimensional accuracy of a CAD model, but will have a superior mesh, which lends itself better to rendering and simulating geometry.
3D model preparation becomes crucial when transitioning between these modeling techniques or when gearing up for the rendering phase. An in-depth understanding of CAD and Polygonal Modelling ensures that the transition is seamless and that the final render or simulation showcases the model in its best light.
Whether you’re refining the precision of a CAD design or optimising the mesh of a Polygonal model, the art of 3D model preparation can make or break the final outcome.
By emphasising proper model preparation, designers can navigate the unique challenges of each method and bring their digital visions to life with unparalleled clarity and detail.
What is design intent and why is it important?
Design Intent is the considered approach that a designer applies to their modelling process. It is always important that models are well considered from the off and are not as we call in the industry ’botched’. Regardless of whether you are using a CAD or Polygonal modelling method, without a considered approach, it is likely that the model will typically not import well for high level rendering.
Issues that are commonly experienced without applying design intent include but are not limited to:
- vertices not being welded;
- overlapping faces;
- gaps in the models etc.
Without a “solid” mesh you will struggle.
3D model preparation is intrinsically tied to the principle of Design Intent. This preparatory phase serves as the bridge between the initial design concept and its final execution in the digital realm. When designers give priority to the intent behind their designs, it facilitates a smoother journey during the 3D model preparation stage.
By anticipating and addressing potential issues, like unwelded vertices or overlapping faces, early in the design phase, the likelihood of encountering discrepancies during rendering diminishes.
The clear design intent is a foundation upon which successful 3D model preparation is built, ensuring that the final visual output aligns with the designer’s original vision and is free from common modeling pitfalls.
Don’t forget the nuts and bolts
It is important that all parts and elements are reproduced in a realistic way from the start. This means that every separate part on the real-world object needs to be separate in the 3D model. This will make materialising and then animating your models that much easier.
Now parts that are often missed when modelling are the fixings, and we know all too well that the last thing an artist wants to do is go through the model adding in every nut and bolt. But this is key to achieving the photo-realistic renders that we all want to see.
It’s these small details such as fixings, sticker recesses, split lines, and text embossing, which will elevate your renders to the next level.
Now sometimes it is the case that a client will provide us a multi-part model that has all these details, but it unfortunately will import as one object. Fortunately, you will often find that in most 3D modelling packages you can grab elements and split them off from the mesh or alternatively you can create this separate element hierarchy within the object as a 3D artist.
Remember, it’s the meticulous attention to detail that differentiates a good render from a great one. Ensuring that every component, no matter how minute, is accurately represented, not only ensures fidelity to the original object but also enhances the depth and realism in the final render. Whether it’s detaching elements from a single mesh or crafting a hierarchical structure within the object, these steps in 3D model preparation are pivotal.
It’s a testament to the saying that ‘the devil is in the details.’ By investing time in these nuances, artists lay the groundwork for a seamless rendering process, emphasising the role of comprehensive 3D model preparation in achieving lifelike and visually striking results.
Fillets are your friends
The 3D space is the same as the real-world space and follows the same laws. For example, one must ensure filleted/chamfered edges on all parts to ensure the correct interaction of light. Nothing in reality is perfectly sharp and requires a sort edge if only 0.01mm of a fillet it will benefit your renders.
During the 3D model preparation process, it’s essential to remember these natural principles that govern both our tangible and digital realms. Incorporating even the tiniest of fillets can profoundly influence how light interacts with your model, resulting in more realistic and dynamic renders.
Keep your model tree tidy
Similarly, when exporting different models and file types, the need for separating the parts can extend into the layer tree as well; or in the case of Keyshot can require different model sets to represent changes in texture or colour also.
Many of our tests have shown that GLB and USDZ models can retain such information that affects the output. This is the first place to experiment if you are getting part or material issues upon export and can quickly solve some of the calculations the AR files make to distinguish between elements.
A cluttered or haphazard tree can lead to inefficiencies and misinterpretations, especially during the export phase. By ensuring each part, layer, and set is clearly defined and logically structured, artists can streamline the rendering and exporting processes, minimizing potential glitches or inaccuracies.
Whether you’re aiming for optimal AR file interpretations or seamless transitions between textures and colours, a tidy model tree is the backbone of effective 3D model preparation. It’s the structured approach that ensures consistent, high-quality results every time.
…Now, the points so far have been applicable to both CAD and Polygonal modelling. However, there are a few additional points to consider when modelling with polygons…
3D model preparation: Working with polygons
As mentioned above the need for welded vertices cannot be stressed highly enough, especially for an AR export. A welded part is a closed mesh and that means that no light will pass through. It means that you can align the normal to the real world and guarantee the highest quality base for rendering.
Just as a moulded plastic part for a toy would be closed and without access to the inner shell, we must ensure that this closed object is produced in 3D. You will find that this is especially useful with glass and the refraction of light on a bottle for example which also has volume.
-
Connected edges
One common issue we find is when edges or faces overlap. When two parts slot together, they do so without intersection in the real world (at least not to their fundamental volumes) so when producing something that fits into another part it is essential that these elements do not clash in the 3D space or strange artifacts will appear. This occurs more often than we like even as professional 3D artists, so it is important to correct them in the 3D model preparation face rather than fixing them in post.
-
Clean topology
Clean topology is made up of lines and curves that follow the form of a product or part. If one can use the lines of the mesh to follow the form of the shape including its neighbouring polygons, then one can more accurately represent the way light bends over the object. Understanding this crucial concept will tremendously impact your 3D model preparation and, your resulting renders.
-
Centralise all individual pivots
During our work with USDZ and GLB AR Models, we have discovered that the requirement for part centralisation of pivots is essential. Each part should have its pivot point aligned within its boundaries and separated from the group to which is it bound (if objects are split into groups) so that when exported into the AR space it will calculate the centre of each part relative to the point of origin of the main model. Without this step, it is possible to have parts exported in different locations to what is visible in the viewports. This is a key element in proper 3D model preparation to ensure accurate renders.
-
Optimise polygon and tri count
In 3D model preparation, you have to remember a key concept: The higher the number of polygons in a model the larger it is and the more calculation points there are. The benefit of these high poly models is quality. Typically, if you have a denser mesh then you have more smoothing points such as you would on a curve. A circle of 180 points will have an edge between each point. A circle of 360 points will have a shorter edge between points and could be expressed as twice as smooth.
There are now visual calculation tools that can display lower poly meshes with more smoothing and options for high to low-poly baking for game engines.
When it comes to AR you want the smallest file size possible. This will be the main challenge. There is a trade-off for quality vs. load speed and in this day and age, nothing is more impressive and important than high quality for the lowest memory cost. This balance can only be structured and found during extensive testing but ideally, you are aiming to produce something between 5mb and 100mb.
-
The difference between Quad and Tri meshes
Typically, the requirement of quad or tri meshes will depend on the software you are using. Software such as 3DS Max will prefer quad meshes and software like Keyshot will want a tri mesh. If you are doing simulation or AR models, then knowing the difference between the two and how your software will work with each type of mesh is a need to know before you begin your 3D model preparation so that you do not double your workload. Again, there are many tools that can quickly convert your mesh from one to the other but only if all the previous practises have been observed.
-
UVW unwrapping
We have also found that differences in UWV unwrapping and UWV mapping with standard primitives also can have varied results. One would reasonably assume that the UWV unwrap will be retained in all instances of export, but that assumption would be wrong. For specific parts or objects, standard UVW mapping often offers superior results and smaller file sizes, whereas unwrap maps can lead to more pixelated textures due to increased scaling. Keep this in mind as you learn proper 3D model preparation as it may just save your project down the line.
Conclusion
In the multifaceted arena of 3D design, the choice between CAD and Polygonal Modelling hinges on specific project needs and desired outcomes. While CAD excels in precision, especially for manufacturing applications, its limited mesh control can pose challenges for 3D rendering. Conversely, Polygonal Modelling, with its versatile mesh configurations, proves optimal for rendering and simulations, albeit without the pinpoint accuracy of CAD.
Ultimately, understanding the intricacies of both methods enables designers to harness their unique strengths, ensuring impeccable results tailored to each project’s demands.”
