diff --git a/exp/board_detect.py b/exp/board_detect.py
--- a/exp/board_detect.py
+++ b/exp/board_detect.py
@@ -3,7 +3,6 @@ import sys
 sys.path.append("../src")
 
 import os
-import math
 import random
 import itertools
 import logging as log
@@ -15,6 +14,7 @@ import scipy.ndimage
 import scipy.signal
 
 from geometry import Line
+from ransac import DiagonalRansac
 from annotations import DataFile,computeBoundingBox
 from hough import show,prepareEdgeImg,HoughTransform
 from analyzer.epoint import EPoint
@@ -125,6 +125,16 @@ class BoardDetector:
 		transformed=cv.warpPerspective(rect,matrix,(self._rectW,self._rectH))
 
 		# determine precise board edges
+		intersections=[]
+		for p in lines[0]:
+			for q in lines[1]:
+				intersections.append(p.intersect(q))
+		sack=DiagonalRansac(intersections,19)
+		diagonals=sack.extract(10,2000)
+		log.debug("diagonals candidates: %s",diagonals)
+		for line in diagonals:
+			self._drawLine(linesImg,line,[0,255,255])
+		show(linesImg,"diagonals candidates")
 
 	def _detectRough(self,img,filename):
 		corners=self._annotations[filename][0]
@@ -191,7 +201,8 @@ class BoardDetector:
 
 		return matrix
 
-	def _drawLine(self,img,line):
+	def _drawLine(self,img,line,color=None):
+		if not color: color=[0,255,0]
 		(h,w)=img.shape[:2]
 		corners=[EPoint(0,0),EPoint(w,0),EPoint(0,h),EPoint(w,h)] # NW NE SW SE
 		borders=[
@@ -207,7 +218,7 @@ class BoardDetector:
 		if any(abs(x)>10**5 for x in [*a,*b]):
 			log.debug("ignored")
 			return
-		cv.line(img,(int(a.x),int(a.y)),(int(b.x),int(b.y)),[0,255,0])
+		cv.line(img,(int(a.x),int(a.y)),(int(b.x),int(b.y)),color)
 
 
 if __name__=="__main__":