Index: detour/4_appendix.html
===================================================================
--- detour/4_appendix.html	(revision 902)
+++ detour/4_appendix.html	(revision 903)
@@ -185,3 +185,25 @@
 detour calculation this is a bit worse, because not the whole bent network is
 moved, only the tiny veryical line segment in the middle between b and c so
 the drawing on c becomes something like d.
+
+<h4> 4.1.8. Geometry: blocking spiral </h4>
+<p>
+In case of the following spiral (blue net), the low level algorithm is unable
+to find the otherwise clearly available path for N1. The reason is that this
+is the "one endpoint in the hull, other endpoint outside of the hull" case,
+which means a clear sight of line is searched between the inner endpoint
+and the naked hull.
+<p>
+<div class="img"><center>
+<p><img src="img/ex_sprial.png">
+<p>Figure 4/8. Spiral can block the low level hull based algorithm.
+</center></div>
+<p>
+Note: the problem is not present if the blue net is split into two sections
+anywhere on the east or south wall (to the right from the conflict), because
+each section is searched separately. That is, the inner part of the spiral is
+in conflict first, which can be detoured through the second segment, then the
+second segment conflict is resolved without considering the first segment, then
+the first segment is conflicted again, etc. So the blocker is not that the
+final path is a spiral.
+
Index: detour/img/Makefile
===================================================================
--- detour/img/Makefile	(revision 902)
+++ detour/img/Makefile	(revision 903)
@@ -5,6 +5,7 @@
 	ex_multi1.png \
 	ex_order.png \
 	ex_osc.png \
+	ex_spiral.png \
 	ex_topo.png \
 	ex_zigzag.png \
 	geo_go_around.png \
Index: detour/img/ex_spiral.lht
===================================================================
--- detour/img/ex_spiral.lht	(nonexistent)
+++ detour/img/ex_spiral.lht	(revision 903)
@@ -0,0 +1,292 @@
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+   offs_y = 0.0
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+     4
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+ ha:pixmaps {
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+}
Index: detour/img/ex_spiral.png
===================================================================
Cannot display: file marked as a binary type.
svn:mime-type = application/octet-stream
Index: detour/img/ex_spiral.png
===================================================================
--- detour/img/ex_spiral.png	(nonexistent)
+++ detour/img/ex_spiral.png	(revision 903)

Property changes on: detour/img/ex_spiral.png
___________________________________________________________________
Added: svn:mime-type
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