Using CAD models vs 3D scans for Model Targets

In this article, we compare Model Targets generated from a CAD model and Model Targets generated from a 3D scans.

There are two ways of acquiring a model for tracking. From a CAD model and from a 3D scan.

  • Model Targets from CAD allows you to recognize objects by shape using pre-existing 3D models. It is likely that a CAD model is available when the object is industrial equipment, a vehicle, toy, or consumer product.
  • Model Targets from a 3D scan are Model Targets generated from 3D scans when a CAD model is not available.

Prerequisites

Model Targets require the CAD model and its physical counterpart. If a CAD model is available it is usually ready to be imported into the Model Target Generator (MTG) without pre-processing. A variety of file formats are supported in the MTG but consider formats that retain the unit scale.

Model Targets from a 3D scan are digital reconstructions based on the physical object. High quality images of the physical object in its entirety are used to reconstruct a digital model mesh with textures. We recommend one of the tested and verified photogrammetry software tools to reconstruct your 3D model. Note that some reconstruction tools still require you to post process the model in a 3D modeling software, either to reduce file size, complexity, or re-scaling before importing it into the MTG.

For more information on supported formats and supported objects for Model Targets, please see Model Targets Supported Objects and CAD Model Best Practices.

Differences

Model Targets from CAD

Model Targets created from CAD work well in many different environments and for many types of objects due to Vuforia’s capabilities in edge and physical feature tracking. We recommend using Model Targets from CAD models for industrial settings, tools, medicinal equipment, reflective objects, and cars. In addition, Model Target detection and tracking is based on the shape of the object and therefore also works if the object is not well textured or its appearance varies – e.g. different colors on cars or different textures for tools or toys.

Compared to a Model Target made from a 3D scan, a ready CAD model that is true to the physical object is faster and easier to work with as you avoid mismatches that is sometimes introduced from the scanning approach. For example, lighting and shadows on the object can be transferred while scanning, or some reflective and transparent materials won’t be picked up by the scanner .  

In general, using existing CAD data over creating a 3D scan is always preferrable if such CAD data is available.

Model Targets from a 3D scan

If no CAD data is available for generating a Model Target, a mesh can be created from a 3D scan with a photogrammetric model reconstruction. However, this will require your model to be somewhat well textured, non-reflective, and the physical object available to you to scan.

Compared to a Model Target from a CAD model, it is challenging to get a true digital replica of the physical object, unless a high-end photogrammetry solution is selected. Creating a 3D Model using photogrammetry has some advantages though; sculptures, natural objects, immovable objects, and hand-crafted unique products are suitable to scan and track as a Mode Target.

When an object is scanned, the texture is included and often accurately represents that of the physical object. Therefore, when a Model Target is generated from a 3D scan, the object will be tracked using the texture by setting the realistic optionin the MTG. This can prove advantageous for objects that lack visual features and clear edges.

In cases where your object is highly textured, but texture varies significantly between objects (e.g., for wooden objects), Model Targets from a CAD model will give you better results. Also, matte and highly reflective objects are difficult to capture with photogrammetry.

The following table summarizes the recommended approaches for object tracking.  

Tracking Feature

Suitability

Model Targets from CAD

Suitable for objects with corresponding CAD Models.

Examples include 3D printed objects, cars, equipment, tools, industrial objects, consumer appliances, all with or without texture.

Model Targets from a 3D Scan

Useful when a CAD model of the object is not available. Examples include industrial customized objects or equipment, natural objects, statues.

Non-reflective and dark matte objects may not work well.

Small and Large Objects as Model Targets

Consider the following aspects when using small objects as Model Targets:

  • Scanning objects smaller than a few centimeters usually doesn’t provide a 3D model accurate enough for Model Target tracking.
  • A small object with a matching CAD model can work better but such small objects require users to move much closer to the object to detect and track.

There is no specific limit on how large a Model Target can be:

  • But users should not be able to move into or inside the object.
  • Large objects also possess more detail and complexity which likely oversteps the threshold for our supported 3D models; even when simplified.
  • The larger Model Target also impacts the performance on devices, and users may find the experience to lag and have long loading times.