Girdle thickness is measured in 720 directions in steps of 0.5 degrees. The thickness of the girdle any given direction is measured by intersecting the vertical plane that defines the direction with the facets that constitute the girdle. HPOxygen finds the upper and lower points of the intersection between the girdle and the vertical plane. The difference between the Z coordinates of these points (along vertical axis) is the final thickness of the girdle in the given direction.
If there are extra facets on the girdle, they may be treated in two different ways
- in case if the extra facet has less than 15° deviation from the girdle (steep girdle extra facet), the extra facet is included into the girdle for the purposes of this measurement
- more than 15° (shallow girdle extra facet), the extra facet is not included.
Unlike Crown height or Pavilion depth measurements, no virtual model is used.
The obtained arrays of values are used to draw the involutes of the girdle surface and to determine the bezel, valley and bone girdle thicknesses. The valley, bezel and bone girdle thicknesses may be measured in at most 16, 8 and 8 points accordingly for most rounded cuts. These girdle thicknesses are measured using a virtual cut without Extra facets.
