3D Dynamic Scanning

Background

[Dynamic foot scanning. Prospects and limitations of using synchronized 3D scanners to capture complete human foot shape while walking (Schmeltzpfenning et al, 2010)]

There has been a tremendous technical development in foot measurement devices leading to a major improvement in the objective analyses of human foot shape. However, standard measurement devices are still limited to static conditions. In order to characterize the changes in foot shape (e.g. arch height during walking and running) investigators currently use plantar pressure plates, three-dimensional motion capture systems and two-dimensional video-based analysis systems. However, all three techniques have major limitations with regard to detecting the shape of an object.

To capture the 3D - information of a moving object with an inconsistent shape like the human foot, there are currently two approaches conceivable: the stereo matching method and the structured light method.
The stereo matching method, as a passive technique without texture projection, is based on triangulation of multiple synchronized cameras. The main disadvantage of this method, however, is the intricate correspondence between images from multiple views.
The structured light method uses a projector–camera system as an active device with defined light patterns projected on the moving object (see pictures below). The correspondence between images is therefore easily solved. Furthermore, information on depth is more precise, especially by applying the phase-shift technique, and noise is reduced compared to a camera–camera system. The structured light method is being applied by the ViALUX zSnapper system that is used in this research project.

                                                                                       
               Picture: Höfling et al. (2004)

Dynamic 3D scanning results in point clouds, i.e. mathematical data sets of x, y, z coordinates of great amounts of topographical points. Thanks to the development of appropriate software tools and methods, these data sets can be processed and analyzed automatically. Characteristic parameters for the development of shoe lasts, shoe design, orthotics design, foot modeling and other uses can be automatically extracted using these tools and methods.

ViALUX zSnapper System

The basic principle of operation for the ViALUX zSnapper 3D Scanners is the phase encoded photogrammetry which is a version of full-field triangulation and represents a technology advancement for the well-known and precise white light scanners. All ViALUX scanners use blue LED light which is a significant practical improvement, e.g. for the suppression of ambient light influence. The zSnapper scanner captures a full section of the 3D surface in a single shot. A sequence of pre-defined patterns is projected onto the object and a camera takes synchronized records from a different perspective view. The 3D reconstruction software calculates an independent (x,y,z) coordinate for each single pixel of the camera.

Both, digital camera and digital projector can be treated as an equivalent unit forming a stereo pair in the phase encoded photogrammetry. Both are completely calibrated so that the second camera (frequently seen in other scanners) is not longer necessary. 3D surface data can be measured for all surface points that are visible in the camera image and are illuminated by the projector at the same time.

The "zSnapper multiple" configuration contains multiple scan units, synchronized and pre-calibrated as an ensemble. The system delivers 3D data that are instantly in the same world coordinate system. In this way, the zSnapper scanners are capable of recording dynamic 3D scenes with comprehensive data from all sides. Therefore, with this measurement setup it is possible to capture the entire foot shape including height, circumferences, width and length measures during walking. Capturing plantar data is possible when a glass platform is integrated into the walkway.

Unlike other pattern switching scanner devices, the described technique provides the ability to combine high resolution with a short shutter time (<1.0 ms) and short recording time which results in a maximum 3D video frame rate of 49 fps for a five-piece zSnapper system.

 

Measurement setup

The three research partners each have a distinct measurement setup with specific characteristics and features, in line with the specific needs required for the respective workpackages in this project.

Thomas More - MOBILAB

The five-piece ViALUX scanner ensemble is built-in in the fully equipped gait analysis lab of MOBILAB. This enables recording other biomechanical parameters simultaneously with the 3D scanner data. Ground reaction forces for example, can be measured simultaneously by means of the glass force plate under which one of the ViALUX scanners is mounted. The other 4 ViALUX scanners can be assembled and disassembled in an easy and flexible way.

                                                               

KU Leuven

At KU Leuven, in vitro experiments were performed. The motion of cadaver feet is measured during simulated gait. The advantage of in vitro measurements is that invasive bone pin markers can be used to measure individual bone motion with high accuracy. In addition, 3D dynamic scanning is used to dynamically measure the foot surfaces during the same motion. The combined measurement of individual bone motion and foot surfaces provides a valuable dataset for validation of the methodologies developed in this project.

Sportmedizin Tübingen

The multi-sensor system DynaScan4D was developed in a former corporation between ViALUX and the Sportmedizin Tübingen (Schmeltzpfenning, 2009). The system is attached on a 4.6m long and 0.8m high walkway. Five ViALUX scanner-units are installed above (4) and below (1) the glass plate and allow the measurement of static and dynamic 3D foot scans. Additionally, a plantar pressure measurement system (EMED, Novel GmbH, Munich) as well as a light barriers system are integrated. The DynaScan4D can be built up in different locations and allow capturing huge sample sizes.