Calibration & Setup
This is a manual to guide you through the automatic spatial alignment of a multi-sensor setup comprising of 4 Intel Real Sense cameras. The proposed method is reliant on an easily-assembled calibration structure which lifts the requirement of placing/gluing markers onto it. In essence, it includes two independent steps in order to achieve high quality estimations. Firstly, given as an input a quadraple of depth images (180x320 px) it utilizes machine learning techniques to produce initial estimations. Secondly, towards further refining the initial results, a graph-based optimization scheme is used to maximize the overlap of point-clouds of neighboring viewpoints.
The goal is to deliver an easily-assembled reference structure for the calibration procedure to the public. Thus, the proposed structure requires 4 low-cost and commercially available packaging boxes from the IKEA, and specifically the JÄTTENE boxes. In practice, the calibration structure could be assembled using any 4 boxes, sized 56 x 33 x 41 cm each.
Since the proposed calibration structure does not require markers, users should only pay attention in placing the boxes, one on top of each other following a 90o rotational pattern, as depicted in the following pictures. Snapping is performed using each respective bottom boxes sides.
The first image shows the assembling procedure from a diagonal perspective. For more descriptive design we use color-coded representation. The first (bottom-most) box is colored in red, the second in green, the third in blue while the last (top-most) is depicted in yellow.
The succeeding image displays the identical positioning of the boxes as viewed from the front-view.
And this last image depicts the corresponding calibration procedure from the top-view.
The formerly placed calibration structure acts as the global coordinate system anchor.
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The setup requires all 4 Intel RealSense sensors to be placed perimetrically around the calibration structure and looking inwards (i.e., towards the structure).
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In order to capture the desired object in full-360o, sensors should be placed approximately at 90o intervals,
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Importantly, towards achieving better performance during the graph-based refinement step, sensors should be positioned diagonally, which means that planar sides of the structure look in-between two adjacent sensors.
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All viewpoints should target the middle of the structure in a way that the structure is depicted at the center of the received images both horizontally and vertically.
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Considering the specific field-of-view of the Intel RealSense and with a view to capturing a standing person at the center of the capturing space, all sensors must be positioned at a distance from the structure ranging from 1.75 to 2.2 meters.
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Finally, the distance from the ground of all sensors must be between 1.1 and 1.5 meter.
An outline of the appropriate positioning of sensors is depicted in the following figure.
