diff --git a/exp/stone_detect.py b/exp/stone_detect.py
--- a/exp/stone_detect.py
+++ b/exp/stone_detect.py
@@ -1,5 +1,9 @@
+import sys
+sys.path.append("../src")
+
 import os
-import sys
+import math
+import heapq
 
 import cv2 as cv
 import numpy as np
@@ -8,6 +12,13 @@ import scipy.ndimage
 
 from annotations import DataFile,computeBoundingBox
 from hough import show
+from analyzer.epoint import EPoint
+
+
+class NeighboringPoint(EPoint):
+	def __init__(self,x,y):
+		super().__init__(x,y)
+		self.neighbours=[]
 
 
 def kmeans(img):
@@ -27,38 +38,79 @@ def quantize(img,centers):
 	return pixels
 
 
-def filterContours(contours,bwImg,stoneDims):
+def filterStones(contours,bwImg,stoneDims):
 	contourImg=cv.cvtColor(bwImg,cv.COLOR_GRAY2BGR)
 	res=[]
 	for (i,c) in enumerate(contours):
 		keep=True
-		print(i)
 		moments=cv.moments(c)
 		center=(moments["m10"]/(moments["m00"] or 1), moments["m01"]/(moments["m00"] or 1))
-		print("center:", center)
 		area=cv.contourArea(c)
-		print("area:",area)
 		(x,y,w,h)=cv.boundingRect(c)
-		print("bounding box:",(x,y,w,h))
 		if w>stoneDims[0] or h>stoneDims[1]*1.3 or w<2 or h<2:
 			cv.drawMarker(contourImg,tuple(map(int,center)),(0,0,255),cv.MARKER_TILTED_CROSS,12)
 			keep=False
 		coverage1=area/(w*h or 1)
-		print("coverage1:",coverage1)
 		hull=cv.convexHull(c)
 		coverage2=area/(cv.contourArea(hull) or 1)
-		print("coverage2:",coverage2)
 		if coverage2<0.8:
 			cv.drawMarker(contourImg,tuple(map(int,center)),(0,127,255),cv.MARKER_DIAMOND,12)
 			keep=False
-		print()
 		if keep:
-			res.append(c)
+			res.append((EPoint(*center),c))
 			cv.drawMarker(contourImg,tuple(map(int,center)),(255,0,0),cv.MARKER_CROSS)
+	print("accepted:",len(res))
+	print("rejected:",len(contours)-len(res))
 	show(contourImg)
 	return res
 
 
+def computeDistances(points):
+	n=len(points)
+	res=np.zeros((n,n),dtype=np.float32)
+
+	for (i,a) in enumerate(points):
+		for (j,b) in enumerate(points):
+			if j<i: continue
+			elif j==i: res[i,j]=0
+			else:
+				res[i,j]=res[j,i]=a.dist(b)
+
+	return res
+
+
+def collectNeighbours(points):
+	# we could do this in O(n log n)
+	# doi:10.1007/BF02187718
+	# https://link.springer.com/content/pdf/10.1007/BF02187718.pdf
+	""":param points: [EPoint, ...]
+	:return: [(k_i,dist_i) for i in range(4)]"""
+	neighborhood=[NeighboringPoint(p.x,p.y) for p in points]
+	dists=computeDistances(points)
+	for (i,a) in enumerate(points):
+		neighbours=heapq.nsmallest(4,enumerate(dists[i]),key=lambda x: x[1] if x[1]>0 else 1000)
+		neighborhood[i].neighbours=[neighborhood[j] for (j,d) in neighbours]
+	return neighborhood
+
+
+def growLine(r,s):
+	""":param r: NeighboringPoint
+	:param s: NeighboringPoint
+	:return: NeighboringPoint or None"""
+	u=s-r
+	alpha=math.atan2(u.y,u.x)
+	t=None
+	beta=alpha+math.pi # -alpha
+	for t_ in s.neighbours:
+		v=t_-s
+		beta_=math.atan2(v.y,v.x) # beta_ in (-pi, pi]
+		if abs(abs(alpha-beta_)-math.pi)>abs(abs(alpha-beta)-math.pi):
+			beta=beta_
+			t=t_
+	if abs(alpha-beta)<math.pi/12: return t
+	else: return None
+
+
 if __name__=="__main__":
 	filepath=sys.argv[1]
 	annotations=DataFile(sys.argv[2])
@@ -92,4 +144,25 @@ if __name__=="__main__":
 	print("stone dims:",tuple(x/2 for x in stoneDims),"-",stoneDims)
 
 	(contours,hierarchy)=cv.findContours(stones,cv.RETR_LIST,cv.CHAIN_APPROX_SIMPLE)
-	filterContours(contours,stones,stoneDims)
+	stoneLocs=filterStones(contours,stones,stoneDims)
+	neighborhood=collectNeighbours([point for (point,contour) in stoneLocs])
+
+	linesImg=cv.cvtColor(np.zeros((h,w),np.uint8),cv.COLOR_GRAY2BGR)
+	cv.drawContours(linesImg,[c for (point,c) in stoneLocs],-1,(255,255,255),-1)
+	for p in neighborhood:
+		cv.drawMarker(linesImg,(int(p.x),int(p.y)),(255,0,0),cv.MARKER_CROSS)
+
+	for p in neighborhood:
+		for q in p.neighbours:
+			length=1
+			while True:
+				q_=growLine(p,q)
+				if q_:
+					q=q_
+					length+=1
+				else: break
+			if length>1 or True:
+				print(length,p,q)
+			cv.line(linesImg,(int(p.x),int(p.y)),(int(q.x),int(q.y)),(255,255,0),min((length+1)//2,3))
+	show(linesImg)
+	cv.imwrite("/tmp/img.png",linesImg)