diff -urN rt_v18/cross.py rt_v19/cross.py
--- rt_v18/cross.py	2018-04-07 23:36:02.000000000 +0900
+++ rt_v19/cross.py	2018-04-12 09:39:53.000000000 +0900
@@ -61,21 +61,6 @@
 	crs['xy_cond_f'] = lambda x, y: x+y<=1 and -x+y<=1 and y>=0
 	return plane_z0_xy_cond(crs)
 
-def poly_n(crs):
-	n = d.get('n', 3)
-	deg = 360.0 / n
-	rad = mt.deg_to_rad( deg * 0.5 )
-	h = math.cos(rad)
-	w = math.sin(rad)
-	for i in range(n):
-		axi = ax.slide_y(-1).compo( ax.zoom([w,h,1]) ).compo( ax.rot_z(i*deg) )
-		#crs_ = { 'l': axi.tr( 'g2l', crs.get('l') ), 'd': crs.get('d') }
-		crs_ = { 'l': axi.tr_line( 'g2l', crs.get('l') ), 'd': crs.get('d') }
-		if triangle(crs_):
-			crs['t'] = crs_.get('t')
-			return True
-	return False
-
 def ball(crs):
 	# r = 1, c = zero
 	# l = p + v t
@@ -88,6 +73,10 @@
 	c = np.dot( l.p, l.p ) - 1
 
 	ts = mt.quadratic_formula(a, b, c)
+	if not ts:
+		return False
+	if len(ts) > 1 and crs.get('eq_d'):
+		ts = sorted( ts, key=abs )[-1:]
 	ts = sorted( filter( lambda v: v > 0, ts ) )
 	if not ts:
 		return False
@@ -129,6 +118,10 @@
 	c = px*px + py*py - 1
 
 	ts = mt.quadratic_formula(a, b, c)
+	if not ts:
+		return False
+	if len(ts) > 1 and crs.get('eq_d'):
+		ts = sorted( ts, key=abs )[-1:]
 	ts = sorted( filter( lambda v: v > 0, ts ) )
 	if not ts:
 		return False
@@ -186,6 +179,10 @@
 	c = px*px + py*py - pz*pz + 2*pz - 1
 
 	ts = mt.quadratic_formula(a, b, c)
+	if not ts:
+		return False
+	if len(ts) > 1 and crs.get('eq_d'):
+		ts = sorted( ts, key=abs )[-1:]
 	ts = sorted( filter( lambda v: v > 0, ts ) )
 	if not ts:
 		return False
@@ -210,8 +207,13 @@
 	crs['nv'] = v.unit(p)
 
 def cross(crs):
-	l_g = crs.get('l_g')
 	d = crs.get('d')
+	kind = d.get('kind')
+
+	if crs.get('eq_d') and kind in [ 'square', 'circle', 'triangle' ]:
+		return False
+
+	l_g = crs.get('l_g')
 	l2g = d.get('l2g')
 	#crs['l'] = lstx.tr( l2g, 'g2l', l_g )
 	crs['l'] = lstx.tr_line( l2g, 'g2l', l_g )
@@ -220,12 +222,11 @@
 		'square': square,
 		'circle': circle,
 		'triangle': triangle,
-		'poly_n': poly_n,
 		'ball': ball,
 		'pipe_side': pipe_side,
 		'cone_side': cone_side,
 	}
-	f = dic.get( d.get('kind') )
+	f = dic.get(kind)
 	if not f:
 		return False
 	return f(crs)
@@ -241,7 +242,6 @@
 		'square': plane_z0_nv,
 		'circle': plane_z0_nv,
 		'triangle': plane_z0_nv,
-		'poly_n': plane_z0_nv,
 		'ball': ball_nv,
 		'pipe_side': pipe_side_nv,
 		'cone_side': cone_side_nv,
diff -urN rt_v18/rt.py rt_v19/rt.py
--- rt_v18/rt.py	2018-04-07 23:33:23.000000000 +0900
+++ rt_v19/rt.py	2018-04-12 09:39:53.000000000 +0900
@@ -41,25 +41,21 @@
 
 ref_rate = ut.arg_f('ref_rate', 0.001)
 
-def get_col(data, lights, l_g, video, nest_rate=1.0, ref_len=None):
+def get_col(data, lights, l_g, video, nest_rate=1.0, prev_d=None):
 	if nest_rate < 0.01:
 		return []
 
-	lst = map( lambda d: { 'l_g': l_g, 'd': d }, data )
+	lst = map( lambda d: { 'l_g': l_g, 'd': d, 'eq_d': d == prev_d }, data )
 	lst = ut.filter_lst( lambda crs: cross.cross(crs), lst )
 	if not lst:
 		return []
 
-	if ref_len:
-		lst = ut.filter_lst( lambda crs: crs.get('t') > ref_len * ref_rate, lst )
-		if not lst:
-			return []
-
 	crs = min( lst, key=lambda crs: crs.get('t') )
 
 	cross.nv(crs)
 
-	rtd = crs.get('d').get('rtd', {})
+	d = crs.get('d')
+	rtd = d.get('rtd', {})
 	base = rtd.get('base', 0.3)
 
 	crst = crs.get('t')
@@ -106,7 +102,7 @@
 			return []
 		ref_v = nv * ( 2 * ang_nv_eyev_nega ) + eyev
 		ref_l = line.new( crsp, ref_v )
-		col = get_col( data, lights, ref_l, video, nest_rate * reflect, crst )
+		col = get_col( data, lights, ref_l, video, nest_rate * reflect, d )
 		return col * reflect if col != [] else []
 
 	col_ = reflect_col()
@@ -134,7 +130,7 @@
 			return []
 		ref_v = reflact_v()
 		ref_l = line.new( crsp, ref_v )
-		col = get_col( data, lights, ref_l, video, nest_rate * reflact, crst )
+		col = get_col( data, lights, ref_l, video, nest_rate * reflact, d )
 		return col * reflact if col != [] else []
 
 	col_ = reflact_col()