ActiveTarget – for simplified and automated spatial camera calibrations

The ActiveTarget is a unique solution transforming what was a long and manual spatial camera calibration procedure into a fully automated, highly accurate and easily repeatable process. The watertight ActiveTarget has embedded LED dots in a 20 x 20 array totaling 200 x 200 mm in size. Several targets can be combined to customize the target size and shape to fit your experiment.

The brightness of the LEDs is optimized to assure high quality calibration images. With automatic target detection and encoding of the LEDs’ positions, the software automatically acquires calibration images and creates spatial calibrations for all connected cameras. With ActiveTarget(s) mounted on the dedicated waterproof traverse, called ActiveTarget Traverse, fully automated calibrations in water and air can be performed.

During the automated spatial camera calibration process, the LED’s are turned on and off individually to encode the position of each LED on the target. The encoding of a specific LED’s position is done by the software running a vertical and a horizontal sequence during which the LED’s are turned on and off. For every step of the sequence images are acquired. The software analysis the acquired images and notes if a specific LED is on or off (LED on =1, LED off =0) and generate binary numbers representing the LED’s position on the target. One advantage is that not all markers needs to be visible on the acquired images. If only parts of the target markers are visible the system will still be able to determine the marker location.

Active Image Stitching – for multi-camera setups to cover a large field of view

In a multi-camera setup where all cameras are jointly spatially calibrated using ActiveTarget(s), the user can now seamless stitch together slightly overlapping images (e.g. for PIV or LIF) to cover at large FoV. The analysis method Active Image Stitching takes the image ensembles from the individual cameras as well as calibration information to warp the images into a common frame of reference. This feature is useful in experimental setups where the FoV of a single camera is not enough to cover the area/volume of an experiment at a sufficiently high resolution. One or several ActiveTargets can be stitched together using the Target Connector plates (see ordering information). As example it is possible to combine 2, 3 or even 4 ActiveTargets in-line to create a target up to 800 mm in length (height 200 mm).

Slightly overlapping FoV of 3 cameras. An automated spatial camera calibration using three ActiveTargets in-line is performed
Active Image Stitching applied to slightly overlapping PIV images

A software add-on allowing the use of a PC screen as a target is available as a cheaper but less accurate solution.

Data Sheets and Literature