AQSENSE's Metric Calibration Tool permits the reconstruction of the COP with metric units (cm, mm, etc.) removing the perspective distortion introduced by the scene projection onto the image sensor. In laser triangulation systems, there are several ways to reconstruct a scene: linear scanning, using rotating tables, using robot arms, etc.
The Metric tool accepts range maps obtained from several laser triangulation layouts:
The SAL3D Metric Calibration is also working for special configurations, when having more than one camera-laser system. Please, take a look to the section Special Metric Layouts.
This calibration tool is adjustable for working in different scenarios, one specific for linear scanning (Linear Metric Calibration) and a second one (Static Metric Calibration).
In case of using the Linear Metric Calibration, the linear displacement is characterized by a pulse (e.g. encoder), therefore it is possible to accumulate all consecutive profiles and to obtain the COP from a single RangeMap.
By using the the Static Metric Calibration, the 3D coordinates are obtained from a single profile. Then, The information of consecutive profiles must be merged to get a full COP. For example, in case of using a rotating table, each profile should be rotated in consonance with the rotating axis.
For a human observer, closer objects seem to be bigger than the same objects in a farther position (related to the observer).
The observer has the impression that a long pipe, as looked at from one of its extremes, seems to be decreasing in diameter as the observer looks farther along the pipe.
This is known as Perspective Effect (see following figure) or in terms of 3D acquisition, Perspective Distortion.
Observing the cloud of points and also the ZMap obtained in both situations, it is clear that the proportional reconstruction distortes the object, while the SAL3D Metric reconstruction preserves the original shape.
The Metric Calibration Tool requires the scanning of a calibration pattern to determine the parameters which relate Profiles or RangeMaps coordinates with metric 3D coordinates. Two kind of calibrations are supported: linear and static. For angular calibrations please refer to the Angular Metric Calibration Tool
This approach involves the acquisition of the RangeMap of a specially designed object (see Description of the linear calibration pattern). The procedure return a Metric Configuration (MetricConfig) suitable for mapping RangeMap coordinates to 3D metric coordinates.
All the functionality is provided by a single function of the sal3d::Metric namespace:
This approach only requires a single profile to determine the relation between camera pixels and metric units. This profile should correspond to the projection of the laser plane over the Description of the static calibration pattern.
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