Optical 3D Measurement Technologies at Fraunhofer IOF

High Performance 3D Sensor Network for Real-Time Reconstruction

3D sensors.

3D sensors.

Experimental setup (A).

Experimental setup (A).

3D representation of the reconstructed surface of a male body (B).

3D representation of the reconstructed surface of a male body (B).

Fast, high precision 3D measurement of people and large objects by structured light based methods remains a challenge. Reasons for this are, for example, large datasets which should be processed quickly and different reflection properties of the objects’ surfaces. Furthermore, for the acquisition of people, their motions should be compensated and the structured illumination must not disturb the person.A high-precision 3D sensor network with short latency time for 3D measurements of people and other complex objects up to a size of 2 m x 1 m x 0.5 m has been developed at Fraunhofer IOF. This network consists of several independent 3D sensors operating with structured light projection in the near-infrared (NIR) range.

Application fields of such sensor systems are the apparel industry, fitness and sports, medicine, and industrial production. The main feature of the sensor network is the short latency time of less than 200 ms from image recording to the calculated 3D point cloud. This makes the system real-time capable.

The network consists of several independent 3D sensors, each composed of a projector and two NIR cameras. The projection unit was realized according to the GOBO (graphical optical blackout) principle using aperiodic fringe patterns. The cameras have a 2 MPix resolution and can record up to 110 frames per second. The system operates at 850 nm wavelength. Using appropriate filters, the visible light can be blocked. Each sensor is calibrated separately. Afterwards the positions and viewing directions of all sensors are calibrated in a common world coordinate system with high accuracy.

Each sensor generates a 3D point cloud of object points in its viewing area. Due to the simultaneous 3D measurement by all sensors, a whole body measurement can be realized in a very short time.Figure A shows an example of the sensor arrangement. The network is suitable e.g. for whole body measurements of slow moving people for adapted machine control.

Figure B shows the 3D representation of a measured mannequin.

 

 

Authors: Christoph Munkelt, Daniel Höhne, Peter Kühmstedt, Gunther Notni

Optical 3D Measurement of Glass and Transparent Plastics

Fig. 1: Laboratory setup of an optical 3D-sensor for measuring transparent plastics and glasses.
© Fraunhofer IOF

Fig. 1: Laboratory setup of an optical 3D-sensor for measuring transparent plastics and glasses.

When it comes to non-contact, fast, and highly precise 3D measurements of objects, optical stereo-vision systems developed by the Fraunhofer IOF have proven their efficacy for certain applications in industry and research. Based on active pattern projection, new 3D systems with wavelengths in the near infrared offer accurate, irritation-free 3D measurements of humans, e.g. for applications in the field of human-machine interaction.

The basic principle of these 3D systems is the active projection of optical patterns onto the objects’ surfaces, which works successfully in the visible or near-infrared wavelength range for a multitude of materials. Yet 3D image errors always arise if the optical properties of certain materials such as glass or transparent plastics interfere with the process of diffuse reflection.

Fig. 2: Thermal image of plastic glasses with a thermal pattern on the surface (top). Reconstructed 3D point cloud with color-coded depth information (bottom).
© Fraunhofer IOF

Fig. 2: Thermal image of plastic glasses with a thermal pattern on the surface (top). Reconstructed 3D point cloud with color-coded depth information (bottom).

Fraunhofer IOF has developed a new method which makes the 3D measurement of these reflective or transparent materials possible. For this purpose, thermal patterns (in the infrared about 10 μm) are absorbed from the object’s surface and their re-emission is analyzed with thermographic cameras. The patterns are generated based on a CO2 laser and an adapted GOBO principle which is described in: S. Heist et al.: High-speed three-dimensional shape measurement using GOBO projection, Opt. Laser Eng. Vol. 87 (2016). Glass and transparent plastics become absorbent by changing the spectral range to the thermal infrared.

The top of figure 2 shows a thermal image of glasses made from plastics with a typical thermal pattern on the object surface. A thermal contrast of about 1 to 2 Kelvin between pattern and surface is sufficient for the further image processing. The bottom of figure 2 shows a complete 3D point cloud of the glasses which was reconstructed by correlating the image stacks of two thermal imaging cameras after various pattern projections.

 

Authors: Anika Brahm, Simon Schindwolf, Stefan Heist, Peter Kühmstedt, Gunther Notni