It’s quite simple actually. You determine the distance from the threshold (r) and height above obstacle clearance surface. You need to be above this surface by the following:
A = BG + ISA dev + 4/3 * sqr root(r sqrd * ANP + r sqrd * WPR + r sqrd * FTE + r sqrd * SSE + r sqrd * VAL + r sqrd * ATIS temp)
where BG = body geometry (accounts for reduced wing tip clearance in a turn), WPR = waypoint resolution (compensates for waypoint co-ordinate rounding errors), FTE = flight technical error (allow for stupid pilot who can’t stay on path, nominally 65 feet), SSE = static source error, VAL = vertical angle leg (glide path angle).
Usually a half decent pilot doing the radios will constantly recalc this and advise the flying pilot if they are infringing the obstacle clearance.