This option is useful for highly uneven 1st background grids. A good choice of this parameter is around 70. Should the code fail to construct the search grid due to too many intersecting elements, the error message contains the required mie. It's essential to reserve some of the boundary nodes to preserve its integrity. AGrid automatically reserves those boundary nodes near which the curvature is high.
Cubic spline is used to compute the curvature.
Reserved nodes are never moved, deleted or snapped in the optimization process. However, in order to reduce the number of skew elements left after the geometric run, the reserved nodes are allowed to be deleted in this run. This may cause the boundary to be self-looped. Therefore a check is made at the end of this run to indicate problematic boundary nodes and the user can easily fix it with Gredit. Therefore this option may not be robust and the bi-section method may fail.