INTERFACE SPIntegral;

IMPORT  SPTriang;

TYPE
  Point = SPTriang.Coords;
  Triangle = ARRAY[0..2] OF Point;
  Function = PROCEDURE (READONLY p: Point): LONGREAL;

PROCEDURE OnTriangle(
    READONLY u, v, w: Point;
    func: Function;
    order: CARDINAL := LAST(CARDINAL);
  ): LONGREAL;
  (*
    Computes the integral of function "func" over the spherical
    triangle with corners "p,q,r", using subdivision into "4^order"
    subtriangles and Gaussian qudrature of order 5 (error
    "O(h^6)") on each part. *)

PROCEDURE OnTwoTriangles(
    READONLY pa, qa, ra: Point;
    READONLY pb, qb, rb: Point;
    func: Function; 
    order: CARDINAL := LAST(CARDINAL);
  ): LONGREAL;  
  (*
    Decomposes the intersection of triangles "pa,qa,ra"
    and "pb,qb,rb" into zero or more triangles,
    and calls "OnTriangle" on each of them. *)
  
END SPIntegral.