INTERFACE H3;

     (*
         Oriented projective geometry in three dimensions

         Author: Jorge Stolfi

         Last edited: M. Carrard - 18/05/1993 - Transcricao para modula-3
      *)

IMPORT R3, R4, R4x4;

TYPE
     Point = RECORD c: R4.T END;     (* c[0..3] are coords [w,x,y,z]. *)
     Plane = RECORD c: R4.T END;     (* c[0..3] are coeffs <W,X,Y,Z>. *)
     PMap =  RECORD dir: R4x4.T; inv: R4x4.T END;
     Sign =  [-1..1];

PROCEDURE errmsg( s: TEXT );                    (* Output error messages *)

PROCEDURE mk_point( w,x,y,z: REAL ): Point;     (* Sets res := [w,x,y,z] *)

PROCEDURE mk_plane( W,X,Y,Z: REAL ): Plane;     (* Sets res := <W,X,Y,Z> *)

PROCEDURE test( p: Point; Q: Plane ): Sign;     (* Returns sign of point p
                                                   relative to plane Q:
                                                    +1 in positive halfspace
                                                     0 on the plane
                                                    -1 in negative halfspace
                                                *)

PROCEDURE join( p,q,r: Point ): Plane;          (* Return the plane through
                                                   p, q, and r. *)

PROCEDURE meet( P,Q,R: Plane ): Point;          (* Return the point common 
                                                   to P, Q, and R. *)

PROCEDURE map_point( p: Point; m: PMap ): Point;(* Applies projective map m 
                                                   to point p. *)

PROCEDURE map_plane( P: Plane; m: PMap ): Plane;(* Applies projective map m
                                                   to plane P *)

PROCEDURE comp_map( m,n: PMap ): PMap;          (* Results the composition 
                                                   of m and n, applied in that
                                                   order *)

PROCEDURE dir( frm,tto: Point ): R3.T;          (* *)

PROCEDURE dst( frm,tto: Point ): REAL;          (* *)

PROCEDURE persp_map( obs,foc,upp: Point ): PMap;(* Computes a perspective 
                                                   transformation with given
                                                   viewing parameters.
                                                   obs => scenesys coords of imagesys (0,0,d) (observer)
                                                   foc => scenesys coords to imagesys (0,0,0) (image focus)
                                                   up  => scenesys point to project on imagesys Z axis
                                                 *)

END H3.