Function clearance_above

pub fn clearance_above(
    field: &LayeredField,
    config: &FieldConfig,
    x: usize,
    y: usize,
    w: Scalar,
) -> Result<ClearanceReport, LayeredFieldError>

Distance from w upward (along local +z) to the next surface crossing.

Crossings within tolerance.linear() of w are treated as the reference surface itself, not as a blocker, so standing on a slab does not report zero clearance against that same slab.