Metric Linear Calibration Add-on

The Metric Linear Calibration is a metric calibration system suitable for laser triangulation set-ups with linear movement. In the Metric Calibration Tool page there is a brief description of what it does.

As with the Static Metric calibration it 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.

This linear metric calibration requires the acquisition of a rangemap of a metric calibration pattern. This calibration requires a constant step between all profiles of the rangemap. It is recommended the use of an encoder to trigger the camera (or cameras) at equal steps.

This metric calibration allows to calibrate the laser acquisition set-up without restrictions on the alignment between laser, movement and pattern.

The Metric Linear Calibration uses a different pattern (reference calibration object) than the static for the extraction of the calibration parameters. For more information, please read the Section Linear calibration pattern
Linear Metric Calibration Panel

In order to calibrate the system, the user should introduce the dimensions of the linear pattern. These dimensions can be introduced either in the top table (and the additional height textbox) or by loading the points from file. This file is a txt-plain file containing the following data:

x1 y1 z1
x2 y2 z2
x3 y3 z3
x4 y4 z4
x5 y5 z5
x6 y6 z6
x7 y7 z7
x8 y8 z8
x9 y9 z9
x10 y10 z10
x11 y11 z11
x12 y12 z12

Where the first 12 lines contains the 3D coordinates of the pattern vertices, and the last line contains the metric distance between the top and base plane.

In case the user did not acquire the pattern rangemap, the user can use the "Grab one" button to get a rangemap from the camera, or it can load a RangeMap from file. Thanks to the bottom window, user can observe this rangemap.

If the calibration pattern covers does not cover all the rangemap width, it is recommended to use a calibration ROI. In that case, the user should introduce the first colum (ROI left) and the last column (ROI right) where the pattern is located.

If possible, it is recommended that the pattern calibration covers all the working area.

After calibration, the user can save this metric configuration to a file if desired, for a possible combination with sal3d.

In addition to the accuracy report, user can click on "Compare ideal". In this case the 3D reconstruction of the pattern is compared with an ideal pattern (according to the calibration points). A new window will pop-up showing the disparity between both patterns. To better visualize the errors, it is recommended to set the viewer in "Color disparity" mode.

In case the customer calibrated the lens distortion (see Lens distortion Add-on) before the metric calibration, 3DExpress will pop-up the following message:
You have done a lens calibration. It will be used at this metric calibration. If you don't want to use the lens calibration, please answer Cancel.
In case you want to use the lens calibration parameters together with the metric, you should click on Ok, otherwise, clicking on Cancel, you will calibrate without using the lens distortion parameters.
In case of combining Lens with metric calibration, user should ensure the goodness of the relation between RangeMap coordinates (for the metric calibration) system and Frame coordinate system (for the Lens Calibration). Please take a look on the Section Lens distortion Add-on for more information).

Metric additional outputs

Combined zmaps (one camera and two lasers)

The linear metric calibration allows to calibrate an acquisition system composed by one camera and two lasers. This calibration allows to reconstruct both rangemaps to generate COPs on the same coordinate system.

To generate the combined ZMap, the user should activate the "ZMap combined" checkbox and select the corresponding additional input.

Panel to configure the ZMap output
This option to combine different inputs on a single output is only valid in case of a single camera with multiple ROIs.