Calculation based on control points - TNSB3

14.2 Calculation based on control points

This method first calculates the minimum rectangle that encompasses all cross section points. Within this rectangle the program looks for the best position for control points, trying to minimize the following values:

1. The distance from each point to the cross section. This enables the section to be positioned as close as possible to the cross section.

2. The variation in point distances. It is not enough to say that points are close to the cross section; the distance should also be as similar as possible in all control points.

If you do compensate for the positions of the control points, you can make the alignment disappear as the points "pull" in one direction. In the following figure we have calculated the alignment offset with the three control points (marked with an x).

The cross section can be seen in red, the position of the template over the alignment in white, and in green the calculated position of the template using the control points.

It will appear as displaced upwards, because if you lower the axis, the points on the sides will have a worse evaluation (they will be distanced from the cross section) because the cross section is widened.

Figure 59 - Three Control Points

By adding a fourth point can make the point "pull away" upwards from the calculated position.

Figure 60 - Four Control Points