Any lens objective introduce radial distortion in the image formation. The main effect of radial distortion is that straight lines in the scene appear as curved ones in the image. The "curving" effect is more significant the more distant to the image center are the imaged objects. Some lens manufacturers have a range of "high-end" lenses that incorporate optical correction systems so that the induced radial distortion is minimal.
As a rule of thumb, the bigger is the focal distance to sensor size ratio, the smaller is the induced distortion. However, choosing a long focal distance reverts into smaller field of view, hence the user must deal with this trade-off between field-of-view and distortion. The overall effect of radial lens distortion is a less accurate 3D calibration and RangeMap merging.
The Lens Distortion Tool allows to compute the lens distortion parameters to compensate the radial distortion. These parameters can be later used during the Metric Calibration
SAL3D library allows two types of calibration patterns, chessboard pattern and dots pattern. In both patterns, the number of cells or dots can be modify by the user. In addition, in opposite to other techniques, ONLY a single pattern image is required to compensate the lens distortion. However, more images can be used to get a more accurate solution.
Chessboard pattern is recommended in case of high distortion. In these situations, dots pattern can fail. On the other hand, dots pattern is recommended to increase the accuracy, specially in cases where it is difficult to get a good printing quality. In addition, dots pattern requires that only dots are present on the image.
Chessboard | 
Dots |
|---|
SAL3D contains two different distortion models (tsai and cubic) and some other ones for internal use. The tsai model can be use for simple configurations, and the cubic model allows to compensate more complex lens distortions, like for example, in the case of Scheimpflug adapters.
by 
1.7.6.1