August 31, 2020
Posted by Vikram Sharma, Software Engineering Intern; Jianing Wei, Staff Software Engineer; Tyler Mullen, Senior Software Engineer
Today, we are excited to release the Instant Motion Tracking solution in MediaPipe. It is built upon the MediaPipe Box Tracking solution we released previously. With Instant Motion Tracking, you can easily place fun virtual 2D and 3D content on static or moving surfaces, allowing them to seamlessly interact with the real world. This technology also powered MotionStills AR. Along with the library, we are releasing an open source Android application to showcase its capabilities. In this application, a user simply taps the camera viewfinder in order to place virtual 3D objects and GIF animations, augmenting the real-world environment.
Instant Motion Tracking in MediaPipe
The Instant Motion Tracking solution provides the capability to seamlessly place virtual content on static or motion surfaces in the real world. To achieve that, we provide the six degrees of freedom tracking with relative scale in the form of rotation and translation matrices. This tracking information is then used in the rendering system to overlay virtual content on camera streams to create immersive AR experiences.
The core concept behind Instant Motion Tracking is to decouple the camera’s translation and rotation estimation, treating them instead as independent optimization problems. This approach enables AR tracking across devices and platforms without initialization or calibration. We do this by first finding the 3D camera translation using only the visual signals from the camera. This involves estimating the target region's apparent 2D translation and relative scale across frames. The process can be illustrated with a simple pinhole camera model, relating translation and scale of an object in the image plane to the final 3D translation.
By finding the change in relative size of our tracked region from view position V1 to V2, we can estimate the relative change in distance from the camera.
Next, we obtain the device’s 3D rotation from its built-in IMU (Inertial Measurement Unit) sensor. By combining this translation and rotation data, we can track a target region with six degrees of freedom at relative scale. This information allows for the placement of virtual content on any system with a camera and IMU functionality, and is calibration free. For more details on Instant Motion Tracking, please refer to our paper.
A diagram of Instant Motion Tracking pipeline is shown below, consisting of four major components: a Sticker Manager module, a Region Tracking module, a Matrices Manager module, and lastly a Rendering System. Each of the components consists of MediaPipe calculators or subgraphs.
Diagram of Instant Motion Tracking Pipeline
The Sticker Manager accepts sticker data from the application and produces initial anchors (tracked region information) based on user taps, and user gesture controls for every sticker object. Initial anchors are then sent to our Region Tracking module to generate tracked anchors. The Matrices Manager combines this data with our device’s rotation matrix to produce six degrees-of-freedom poses as model matrices. After integrating any user-specified transforms like asset scaling, our final poses are forwarded to the Rendering System to render all virtual objects overlaid on the camera frame to produce the output AR frame.
The Instant Motion Tracking solution is easy to use by leveraging the MediaPipe cross-platform framework. With camera frames, device rotation matrix, and anchor positions (screen coordinates) as input, the MediaPipe graph produces AR renderings for each frame, providing engaging experiences. If you wish to integrate this Instant Motion Tracking library with your system or application, please visit our documentation to build your own AR experiences on any device with IMU functionality and a camera sensor.
Instant Motion Tracking solution allows bringing both 3D stickers and GIF animations into Augmented Reality experiences. GIFs are rendered on flat 3D billboards placed in the world, introducing fun and immersive experiences with animated content blended into the real environment.Try it for yourself!
Demonstration of GIF placement in 3D
MediaPipe Instant Motion Tracking is already helping PixelShift.AI, a startup applying cutting-edge vision technologies to facilitate video content creation, to track virtual characters seamlessly in the view-finder for a realistic experience. Building upon Instant Motion Tracking’s high-quality pose estimation, PixelShift.AI enables VTubers to create mixed reality experiences with web technologies. The product is going to be released to the broader VTuber community later this year.
Instant Motion Tracking helps PixelShift.AI create mixed reality experiences
We look forward to publishing more blog posts related to new MediaPipe pipeline examples and features. Please follow the MediaPipe label on Google Developers Blog and Google Developers twitter account (@googledevs).
We would like to thank Vikram Sharma, Jianing Wei, Tyler Mullen, Chuo-Ling Chang, Ming Guang Yong, Jiuqiang Tang, Siarhei Kazakou, Genzhi Ye, Camillo Lugaresi, Buck Bourdon, and Matthias Grundman for their contributions to this release.
