UV Layout Best Practices

A SimReady 3D asset has two recommendations when it comes to UV mapping:

• Non-Overlapping UVs

• Use UV Channel 1 only

Every 3D asset that includes complex texture map layouts and is intended for simulation requires a UV mapping process. This results in a flattened 2D representation of the 3D asset so texture maps can be accurately projected on its surface. Any modern DCC app is capable of processing these unwrapped UV Maps.

The resulting UV Map is normalized in UV space using values between 0 and 1. The UV space is defined by two axes, U and V, where U represents horizontal coordinates (X) and V represents the vertical coordinates (Y).

SimReady requires UV maps in order to render 3D assets correctly. Consequently, UV Mapping is an important part of the creation process of assets intended for simulation.

Determining how to unwrap a 3D asset is a matter of personal preference. Creators can use different methods to generate their UVs, and, like the modeling process, there is no single “right way” to do so. What is important is to consider which UV unwrapping approach will be used and trying to be consistent.

Doing so will also ensure that your materials can be upgraded from older material types to newer ones as more advanced materials become available.

Defining Seams for UV Unwrapping

A creator should plan ahead for where their unwrapped UV seams will be located. This will help to prevent the display of unwanted, visible UV Map breaks that can impact the visual fidelity of the asset. Whenever possible, the goal is to place seams where natural transitions occur on the physical object that is being recreated.

Some tileable patterns can also cause seams to be more visible and difficult to hide. Placing seams behind other geometry could be a quick way to troubleshoot this issue. A creator can also weld two UV islands together in order to avoid unwanted seams. In some situations, a creator can leave a small amount of UV distortion (stretching or compression) in order to keep some UV islands together for the sake of better materials rendering. It is important to practice good judgment when making these decisions. Here is an example of good and bad approaches to these types of situations:

Don’t place seams in the middle of holes or geometry

Extending seams to the base of holes adds a tiny bit of distortion, but is better for mapping

Keep the following recommendations in mind when planning UV unwrapping for SimReady 3D assets:

• UV breaks or seams should follow the natural structure of the object

• For more complex 3D models, make sure to place the UV seams away from important viewing angles

• Limit the number of UV islands or shells to help make material creation work easier

• Make sure that there are no overlapping UV shells in the 3D model

• Limit your UV unwrapping workflow to using UV Channel 1 only

• Make sure that UV islands are oriented correctly to help with the natural flow of patterns on texture maps that are intended for the object in question (such as wood grain patterns)

There will be times when separating the 3D asset into parts or GeomSubsets will be necessary. The key in these cases is to be very strategic regarding the placement of UV seams and to hide them whenever possible.

UV Coherence

Working with UVs will require the use of visual aid texture maps (sometimes called UV Grids), that can help to quickly identify where poor orientation and distortion occurs when unwrapping a 3D asset. Modern DDC apps provide users with a couple of UV Grid bitmaps that can be used for this purpose. Creator should also be able to import their own custom texture maps if needed. Usually these texture maps include easily identifiable grid lines, shapes and text that can be used to visualize artifacts or errors on 3D surfaces. Creators can also use these UV grids to understand the overall size or scale of the 3D asset. Keep in mind the following recommendations when reviewing UV map coherence:

• Look for poorly oriented UV shells

• Flipped UVs facing the wrong direction

• Keep UV Grid textures evenly squared to minimize distortion, stretching, or tearing

• Ensure relative scale between UV islands (texel density)

Modern DCC apps include visible aid tools or features that make it easier to identify errors during the UV unwrapping process. Generally, this is done by displaying problem areas using color coding which makes identification of issues more efficient. Most DCC apps also include technologies that facilitate UV packing to help keep texel density homogeneous and organized.

Generally, it is best to target a minimum texel density of 512 pixels/meter for simulation. Currently, we recommend that the maximum texture resolution be kept at 4096x4096 pixels, and non-square textures are allowed. In order to achieve this resolution, UDIMs can be used. However, what is most important is a consistent texel density. If you need help understanding texel density and UDIMs, please refer to these articles:

• Texel Density Tutorial

• Udims Tutorial

Here are a couple of additional tips that can be used to help ensure the UV Unwrapping workflow is consistent:

• Keep all cylindrical UV islands straight so these can be packed in either a horizontal or vertical orientation. This will avoid the introduction of diagonal lines in texture bakes which result in lower resolution and artifacts.

• Avoid creating thin strip UV islands. Instead, straighten them and then attach them to vertical or horizontal UV islands.

• Keep UV islands oriented consistently to help make it easier to stamp fonts, alphas, and logos, as well as applying patterns like directional grains (e.g. brushed metals, wood, or directional scratching) on the 3D models.

• Make sure that UVs are relaxed to maintain proper texel density between all UV shells.

UVs and Real World Scale

It is very important to stay true to real world dimensions when 3D modeling an asset for SimReady. This will impact how the 3D model behaves regarding lighting, animation and physics for example. This level of compliance will also make texturing work easier to troubleshoot. The goal is to create UV islands capable of rendering the correct, real world size of the physical material sample. Most 3D artists target the use of the 1 UV = 1 Meter standard. By following a UV to world scale standard, materials that have been created with real-world size in mind will maintain proper scale as default behavior when applied.

To summarize, 3D assets intended for SimReady require a coherent UV workflow. This will guarantee full fidelity visualization throughout the array of render engines within a simulation platform. We encourage creators to plan ahead before starting work on UV layout to ensure that there is less troubleshooting in later stages of production. Affording this piece of mind early on will assure a more predictable and enjoyable time during the material and texture creation processes.