Version: 16.3.1.167ea6ecff

Lens distortion Add-on

Description

The AQSENSE metric calibration tool does not correct the lens distortion, but the perspective distortion. So, in case the lens distortion is relevant, 3DExpress allows the user to correct the lens distortion before the metric calibration.

In this case, the metric calibration uses the parameters determined during the calibration and adds them to the metric calibration configuration. After this process 3DExpress is able to convert RangeMaps affected by lens distortion to undistorted COPs.

Please, take a look at the section Lens Distortion to get more information of the Lens Distortion and the corresponding calibration patterns.

Usage

To correct the lens distortion, the user should open the Frame viewer of the corresponding camera (by double-clicking on the appropriate input cell). There is a Lens menu in this viewer.

After placing the calibration pattern in front of the camera, the user should click on Lens > Calibrate. After choosing the corresponding pattern, 3DExpress determines the lens distortion parameters. However, for these parameters to take effect, it is necessary to use the Metric Calibration. When the user goes to that page and tries to calibrate, 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.

Calibrating the lens on the AT cameras

In case of Automation Technology cameras, the user should set the camera ROI to full ROI for the lens calibration. Later, during the metric calibration, 3DExpress automatically corrects the offset between the full ROI and the working ROI during the 3D acquisition.

So, it is not needed that the customer selects the mode "Absolute coordinates" on the camera. In case the customer selects this option, during the metric calibration, the user should set the offset to "0" (as in this case, both the lens calibration and the metric calibration are working on the same camera coordinates.

Calibrating the lens on the 3D03 Photonfocus camera

In case of working with the 3D03 camera from Photonfocus, the user should take an image of the lens calibration pattern using all rows of the sensor, but using the same columns used during the 3D acquisition.

Later, during the metric calibration, 3DExpress automatically corrects the rows offset between the lens calibration coordinate system and the metric calibration coordinate system.

Calibrating with a generic 2D camera

In case of working with a generic 2D camera, as 3DExpress can not access to the camera parameters, the user must calibrate the lens distortion using the same ROI used during the 3D metric calibration and during the 3D acquisition.

In case that the user has to work with different ROIs (for example, the ROI is too small for a correct lens calibration), during the metric calibration the user must introduce the offset difference between both ROIs.

During the metric tool calibration, 3DExpress displays a window that allows the user to introduce this ROI offset.

Note
This offset only allows to correct the offset on the Y axis (rows index), so, both ROIs (lens calibration and 3D metric calibration) must have the same offset in the X axis (column index).
lens_calib_generic2D.png
Different working ROIs with the same initial point