FF/FL Define sample lines

This step helps to arrange the sample lines inside each test section (according to the standard).

For each test section:

Choose the appropriate pattern among Parallel and perpendicular and 45 degrees.
Define the Number of sample lines (perpendicular to the main direction or the 45 degrees direction).
If the Compute button is greyed out, the computation would fail: refer to the notes below.
Otherwise, click Compute: a levelness colormap is computed and you can Edit color. In case of failure, refer to the notes below.

A failure means the computation can't be made according to the standard:

increase the number of sample lines (double click the actual number). The FL computation requires a higher cumulative length than FF computation.
rearrange the sample lines in orange (sample line too close to another one) and red (sample line crossing a hole in your cloud):
- automatically:
  - change the pattern mode.
  - change the pattern main direction (only in 45 degrees mode).
- or manually:
  - select one and give it a new position.
  - select one and shorten it using CTRL + MOUSE WHEEL (only in 45 degrees mode).