The Complete PRC/U3D to VRML Conversion Guide

Free-Form Surfaces Support:

PRC/U3D: Full support | VRML: Partial support

VRML Notes:

Limited NURBS support in VRML 2.0

Impact:

Free-form surfaces allow a CAD user to design surfaces with advanced controls over curvature and continuitiy. While these surfaces are common for CAD models (in the form of so-called boundary representations or "B-reps"), they need to be converted to polygonal triangle or quad data to work with most 3D rendering engines - a process called tessellation. In this example, a surface patch is used to describe a part of a curved surface of a product. Without support for this feature, the free-form surface has to be tessellated into quads or triangles.

Geometry Compression Support:

PRC/U3D: Full support | VRML: No support

Impact:

Geometry compression describes the process of compressing the representations of a 3D model's geometry, usually a triangle mesh. 3D geometry compression does not change the topology of a 3D model, but just changes the way that a 3D model and its 3D positions and related vertex data is stored. Geometry compression can be lossy (just like JPEG compression in image processing can be lossy, for example), in which case one might notice slight artifacts like variations in 3D vertex positions (compared to the uncompressed 3D model). However, such differences are often not noticeable. There are only very few standards for geometry compression, like glTF's support of Draco compression and similar extensions.

Quad Meshes Support:

PRC/U3D: Full support | VRML: Partial support

VRML Notes:

Primarily triangle-based with some quad support

Impact:

Quad meshes are a common way to hand-model and edit 3D models. 3D artists get intuitive control and such meshes are also easy to refine, as well as well-suited for creation of skinned animations. However, real-time rendering pipelines and hardware are usually all based on triangles, so if a 3D model should not be edited any more, it is safe to convert quads to triangles (and engines will do this automatically before sending data to the rendering hardware). In this example, a part of a mesh is modeled with quads. Without support for this feature, quads will have to be triangulated, producing a pure triangle mesh.

Texture Compression Support:

PRC/U3D: Partial support | VRML: No support

PRC/U3D Notes:

Basic texture compression for document embedding

Impact:

Texture compression refers to a process of compressing 2D texture images for memory-efficient rendering (and sometimes for efficient transmission). The decompression of compressed texture data is therefore performed on-the-fly during rendering, so that it never has to be stored in unpacked form, but can be kept as-is in GPU memory. Formats supporting texture compression methods, such as the ones offered by glTF through KTX2 containers, therefore allow 3D models to use a smaller memory footprint on the client device during rendering. This can speed up rendering time, and also make it possible to store and use larger amounts of texture data than it would otherwise be possible.

Multiple UV Channels Support:

PRC/U3D: Full support | VRML: Partial support

VRML Notes:

Basic multi-texturing capabilities

Impact:

Multiple UV channels allow the optimized and sophisticated use of various 3D modeling features at once. For example, one can use one set of UVs and 2D texture data to model a tiling texture or procedural material, and another UV set to leverage a global lightmap or occlusion map of the 3D model. In this example, a combination of tiled texture (UV channel 1) and baked ambient occlusion map (UV channel 2) is used. Without support for this feature, one needs to either give up the tiling property (e.g., by using a tool like RapidPipline to bake a single texture atlas), or give up the ambient occlusion map, as only one UV channel will be usable.

Embedded Textures Support:

PRC/U3D: Full support | VRML: No support

Impact:

Embedded textures allow the storage and exchange of an entire 3D model and its materials within a single file, by embedding the texture images directly into the 3D file (and not storing them as separate image files). Without support for this feature, textures have to be stored in separate image files, and referenced from the main 3D model file.

Normal Mapping Support:

PRC/U3D: Partial support | VRML: No support

PRC/U3D Notes:

Limited normal mapping support

Impact:

Normal maps are used to model shading differences that are arising from small geometric details on a surface, such as fabric structures, visible gaps between bricks forming a wall, or rough rock surfaces. In this example, a normal map is used to model a fabric structure. Without support for this feature, the rendered fabric will look smoother than it actually is in the real world, as the fabric structure won't be visible.

Skinned Animations Support:

PRC/U3D: Partial support | VRML: No support

PRC/U3D Notes:

Basic skeletal animation support in U3D

Impact:

Skinned animations are commonly used for 3D character models in interactive applications, such as games or virtual worlds. They make it possible to easily animate the 3D model using a helper structure based on virtual bones, composing a virtual skeleton for animation control. In this example, a skinned animation is used to pose a 3D character. Without support for skinned animations, the 3D model will remain in its default pose, such as the default T-pose.