Status	Rule
  Comment	;; Revison 1:  Intensity Surface-Interpolation for quadrilateral
  Comment	;; Expect better agreement with flatter quads (i.e. Intensity fields closer together)
  Comment	;; Rev. 1: Changed the way vertical slope was handled. Added Case for Pt. P lying anywhere along Edge[1-2]

  Satisfied	yP=y5
  Satisfied	y5=y6
  Satisfied	I5=(y5-y1)/(y4-y1)*I4 + (y4-y5)/(y4-y1)*I1
  Satisfied	I6=(y3-y6)/(y3-y2)*I2 + (y6-y2)/(y3-y2)*I3

  Comment	;;  This is new.   If R5=0 then either a) Edge[1-4] is vertical, or b) Pt. P is sitting along Edge[1-2]
  Satisfied	if OR(x4=x1,yP=y1) then R5=0 else 1/R5=(y4-y1)/(x4-x1) ;; usual slope. m5=1/R5 avoids !DIV0! with condition
  Satisfied	x5=x1+(y5-y1)*R5

  Satisfied	if OR(x3=x2,yP=y2) then R6=0 else 1/R6=(y3-y2)/(x3-x2)     ;; Similar to R5
  Satisfied	x6=x2+(y6-y2)*R6                                                         ;; Similar to x5

  Satisfied	IP=(x6-xP)/(x6-x5)*I5 + (xP-x5)/(x6-x5)*I6