INTERFACE PZGeo3;

(* Miscellaneous geometry tools *)
(* Last edited on 1999-08-06 22:03:36 by hcgl *)

IMPORT LR3;

TYPE
  Point = LR3.T;
  LONG = LONGREAL;

PROCEDURE LinearInterpolate(
    t: LONG; 
    a: LONG; READONLY pa: Point; 
    b: LONG; READONLY pb: Point;
  ): Point;
  (*
    Interpolates linearly the position at time "t" between 
    points "pa" and "b", assuming they have times "a" and "b". *)

PROCEDURE HermiteInterpolate(
    t: LONG; 
    a: LONG; READONLY pa: Point; READONLY va: Point; 
    b: LONG; READONLY pb: Point; READONLY vb: Point;  
    VAR p: Point;
    VAR v: Point;
  );
  (*
    Performs cubic Hermite interpolation for argument "t" given
    positions "pa" and "pb" and velocities "va" and "vb" at times "a"
    and "b". Best used for "t" between "a" and "b". *)

PROCEDURE EstimateVelocityQ(
    a: LONG; READONLY pa: Point; 
    b: LONG; READONLY pb: Point; 
    c: LONG; READONLY pc: Point;
  ): Point;

PROCEDURE EstimateVelocityL(
    a: LONG; READONLY pa: Point; 
    b: LONG; READONLY pb: Point; 
    c: LONG; READONLY pc: Point;
  ): Point;

PROCEDURE EstimateVelocityC(
    a: LONG; READONLY pa: Point; 
    b: LONG; READONLY pb: Point; 
    c: LONG; READONLY pc: Point;
  ): Point;
  (* 
    These procedures return estimates of a curve's velocity at time "b", 
    given its positions "pa", "pb", "pc" at three successive times "a", "b", "c".
    
    EstimateVelocityQ uses quadratic interpolation. It is precise for
    quadratic functions but is unstable when "b" is near "a" or "c".
    
    EstimateVelocityL uses linear interpolation between "(a,pa)" and "(c,pc)".
    It ignores "b" and "pb".  It is therefore robust for uneven intervals,
    but is not precise for quadratics. 
    
    EstimateVelocityC uses a formula that degenerates to linear
    interpolation between "(a,pa)" and "(b,pb)" when "b" is close to
    "c", and to linear interpolation between "(b,pb)" and "(c,pc)"
    when "b" is close to "a".  It thus gives an "unconstrained
    derivative" effect at double nodes, which is useful for
    modeling. It is more robust than EstimateVelocityQ, but 
    is not precise for quadratics. *)


PROCEDURE HermiteCurveLength(
    a: LONG; READONLY pa: Point; READONLY va: Point; 
    b: LONG; READONLY pb: Point; READONLY vb: Point;  
  ): LONG;
  (*
    Computes the approximate length between "pa" and "pb"
    of the cubic curve that interpolates "(a,pa)" and "(b,pb)", 
    with velocities "va", "vb" at those points. *)


PROCEDURE BSplineApproximation(
    t: LONG;
    a: LONG; 
    b: LONG; READONLY Pabc: Point;
    c: LONG; READONLY Pbcd: Point;
    d: LONG; READONLY Pcde: Point;
    e: LONG; READONLY Pdef: Point;
    f: LONG;
  ): Point;
  (*
    Computes the position at time "t" of a cubic B-Spline curve
    with control points "Pabc", "Pbcd", "Pcde", "Pdef",
    and knot sequence "a",... "f".  Assumes "t" lies between "c"
    and "d". *)

END PZGeo3.