From af6762b52d4aea8e6f75c15df0c58be8c0fa28dd Mon Sep 17 00:00:00 2001
From: Matthias Koefferlein <matthias@klayout.de>
Date: Thu, 4 Sep 2025 21:58:46 +0200
Subject: [PATCH 1/4] Fixing issue #2134 ('merged' on edge layers not working
 in DRC)

---
 src/drc/drc/built-in-macros/_drc_layer.rb |  17 +++++++++++++++--
 src/drc/unit_tests/drcSimpleTests.cc      |  11 +++++++++++
 testdata/drc/drcSimpleTests_145.drc       |  22 ++++++++++++++++++++++
 testdata/drc/drcSimpleTests_145.gds       | Bin 0 -> 842 bytes
 testdata/drc/drcSimpleTests_au145.gds     | Bin 0 -> 3290 bytes
 testdata/drc/drcSimpleTests_au145d.gds    | Bin 0 -> 2084 bytes
 6 files changed, 48 insertions(+), 2 deletions(-)
 create mode 100644 testdata/drc/drcSimpleTests_145.drc
 create mode 100644 testdata/drc/drcSimpleTests_145.gds
 create mode 100644 testdata/drc/drcSimpleTests_au145.gds
 create mode 100644 testdata/drc/drcSimpleTests_au145d.gds

diff --git a/src/drc/drc/built-in-macros/_drc_layer.rb b/src/drc/drc/built-in-macros/_drc_layer.rb
index 6c119936d..7eee5f905 100644
--- a/src/drc/drc/built-in-macros/_drc_layer.rb
+++ b/src/drc/drc/built-in-macros/_drc_layer.rb
@@ -5079,6 +5079,7 @@ CODE
     #
     # This method works both on edge or polygon layers. Edge merging forms
     # single, continuous edges from coincident and connected individual edges.
+    # The overlap count is only available on polygon layers.
     #
     # A version that modifies the input layer is \merge.
     #
@@ -5106,7 +5107,13 @@ CODE
     def merged(overlap_count = 1)
       @engine._context("merged") do
         requires_edges_or_region
-        aa = [ @engine._prep_value(overlap_count) ]
+        oc = @engine._prep_value(overlap_count)
+        if self.data.is_a?(RBA::Edges)
+          oc == 1 || raise("'overlap_count' (merged) is only available on polygon layers")
+          aa = []
+        else
+          aa = [ oc ]
+        end
         DRCLayer::new(@engine, @engine._tcmd(self.data, 0, self.data.class, :merged, *aa))
       end
     end
@@ -5114,7 +5121,13 @@ CODE
     def merge(overlap_count = 1)
       @engine._context("merge") do
         requires_edges_or_region
-        aa = [ @engine._prep_value(overlap_count) ]
+        oc = @engine._prep_value(overlap_count)
+        if self.data.is_a?(RBA::Edges)
+          oc == 1 || raise("'overlap_count' (merged) is only available on polygon layers")
+          aa = []
+        else
+          aa = [ oc ]
+        end
         if @engine.is_tiled?
           # in tiled mode, no modifying versions are available
           self.data = @engine._tcmd(self.data, 0, self.data.class, :merged, *aa)
diff --git a/src/drc/unit_tests/drcSimpleTests.cc b/src/drc/unit_tests/drcSimpleTests.cc
index 8e46d2d74..85547ab6b 100644
--- a/src/drc/unit_tests/drcSimpleTests.cc
+++ b/src/drc/unit_tests/drcSimpleTests.cc
@@ -2044,3 +2044,14 @@ TEST(144d_combined_antennas)
   run_test (_this, "144", true);
 }
 
+//  issue 2134
+TEST(145_edges_merge)
+{
+  run_test (_this, "145", false);
+}
+
+TEST(145d_edges_merge)
+{
+  run_test (_this, "145", true);
+}
+
diff --git a/testdata/drc/drcSimpleTests_145.drc b/testdata/drc/drcSimpleTests_145.drc
new file mode 100644
index 000000000..c5c5e094e
--- /dev/null
+++ b/testdata/drc/drcSimpleTests_145.drc
@@ -0,0 +1,22 @@
+
+source $drc_test_source
+target $drc_test_target
+
+if $drc_test_deep
+  deep
+end
+
+l1 = input(1, 0)
+l2 = input(2, 0)
+l3 = input(3, 0)
+
+l1.output(1, 0)
+l2.output(2, 0)
+l3.output(3, 0)
+
+l1.raw.edges.merged.output(100, 0)
+l2.raw.edges.merged.output(101, 0)
+l3e = l3.raw.edges
+l3e.merge
+l3e.output(102, 0)
+
diff --git a/testdata/drc/drcSimpleTests_145.gds b/testdata/drc/drcSimpleTests_145.gds
new file mode 100644
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GIT binary patch
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diff --git a/testdata/drc/drcSimpleTests_au145.gds b/testdata/drc/drcSimpleTests_au145.gds
new file mode 100644
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GIT binary patch
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diff --git a/testdata/drc/drcSimpleTests_au145d.gds b/testdata/drc/drcSimpleTests_au145d.gds
new file mode 100644
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GIT binary patch
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From aed28098f2cb01b9e165894c94f6fa694a2d854f Mon Sep 17 00:00:00 2001
From: Matthias Koefferlein <matthias@klayout.de>
Date: Thu, 4 Sep 2025 23:30:39 +0200
Subject: [PATCH 2/4] First solution, needs more testing

---
 src/db/db/dbEdgePairRelations.cc       | 165 +++++++++++++++++--------
 src/drc/unit_tests/drcSimpleTests.cc   |  11 ++
 testdata/drc/drcSimpleTests_146.drc    |  51 ++++++++
 testdata/drc/drcSimpleTests_146.gds    | Bin 0 -> 510 bytes
 testdata/drc/drcSimpleTests_au146.gds  | Bin 0 -> 7546 bytes
 testdata/drc/drcSimpleTests_au146d.gds | Bin 0 -> 8910 bytes
 6 files changed, 174 insertions(+), 53 deletions(-)
 create mode 100644 testdata/drc/drcSimpleTests_146.drc
 create mode 100644 testdata/drc/drcSimpleTests_146.gds
 create mode 100644 testdata/drc/drcSimpleTests_au146.gds
 create mode 100644 testdata/drc/drcSimpleTests_au146d.gds

diff --git a/src/db/db/dbEdgePairRelations.cc b/src/db/db/dbEdgePairRelations.cc
index a1309898e..5d32bcc27 100644
--- a/src/db/db/dbEdgePairRelations.cc
+++ b/src/db/db/dbEdgePairRelations.cc
@@ -93,15 +93,21 @@ static bool include_zero_flag (zero_distance_mode zd_mode, const db::Edge &a, co
  */
 bool euclidian_near_part_of_edge (zero_distance_mode zd_mode, db::coord_traits<db::Coord>::distance_type d, const db::Edge &e, const db::Edge &other, db::Edge *output)
 {
-  //  Handle the case of point-like basic edge: cannot determine
-  //  orientation
-  if (e.is_degenerate ()) {
-    return false;
-  }
-
   db::Edge g (other);
-  int s1 = e.side_of (g.p1 ());
-  int s2 = e.side_of (g.p2 ());
+
+  //  s1 = side of g.p1 wrt e
+  //  s2 = side of g.p2 wrt e
+  int s1, s2;
+  if (e.is_degenerate ()) {
+    if (g.contains (e.p1 ())) {
+      s1 = s2 = 0;
+    } else {
+      s1 = s2 = -1;
+    }
+  } else {
+    s1 = e.side_of (g.p1 ());
+    s2 = e.side_of (g.p2 ());
+  }
 
   bool include_zero = include_zero_flag (zd_mode, e, g);
   int thr = include_zero ? 0 : -1;
@@ -115,33 +121,49 @@ bool euclidian_near_part_of_edge (zero_distance_mode zd_mode, db::coord_traits<d
     g = db::Edge (g.cut_point (e).second, g.p2 ());
   }
 
-  //  Handle the case of point vs. edge
+  //  Handle the case of point vs. edge/point
 
   if (g.is_degenerate ()) {
 
-    db::Point o = g.p1 ();
+    if (e.is_degenerate ()) {
 
-    if (e.side_of (o) > thr) {
-      return false;
-    }
-
-    double a = e.double_sq_length ();
-    double b = db::sprod (db::Vector (e.p1 () - o), e.d ()) / a;
-    double c = (e.p1 ().sq_double_distance (o) - double (d) * double (d)) / a;
-
-    double s = b * b - c;
-    if (s >= -db::epsilon) {
-      double l1 = std::max (0.0, (-b - sqrt (s)));
-      double l2 = std::min (1.0, (-b + sqrt (s)));
-      if (l1 <= l2) {
+      //  point vs. point
+      if (e.p1 ().distance (g.p1 ()) < double (d)) {
         if (output) {
           *output = g;
         }
         return true;
       }
-    }
 
-    return false;
+      return false;
+
+    } else {
+
+      db::Point o = g.p1 ();
+
+      if (e.side_of (o) > thr) {
+        return false;
+      }
+
+      double a = e.double_sq_length ();
+      double b = db::sprod (db::Vector (e.p1 () - o), e.d ()) / a;
+      double c = (e.p1 ().sq_double_distance (o) - double (d) * double (d)) / a;
+
+      double s = b * b - c;
+      if (s >= -db::epsilon) {
+        double l1 = std::max (0.0, (-b - sqrt (s)));
+        double l2 = std::min (1.0, (-b + sqrt (s)));
+        if (l1 <= l2) {
+          if (output) {
+            *output = g;
+          }
+          return true;
+        }
+      }
+
+      return false;
+
+    }
 
   }
 
@@ -150,10 +172,13 @@ bool euclidian_near_part_of_edge (zero_distance_mode zd_mode, db::coord_traits<d
   double l1 = std::numeric_limits<double>::max (), l2 = -std::numeric_limits<double>::max ();
 
   //  handle the parallel case
+  //  NOTE: a point is "parallel" to an edge.
   if (e.parallel (g)) {
+
     if (std::abs (double (e.distance (g.p1 ()))) >= double (d)) {
       return false;
     }
+
   } else {
 
     double ef = 1.0 / e.double_length ();
@@ -233,16 +258,21 @@ bool euclidian_near_part_of_edge (zero_distance_mode zd_mode, db::coord_traits<d
  */
 static bool var_near_part_of_edge (zero_distance_mode zd_mode, db::coord_traits<db::Coord>::distance_type d, db::coord_traits<db::Coord>::distance_type dd, const db::Edge &e, const db::Edge &other, db::Edge *output)
 {
-  //  Handle the case of point-like basic edge: cannot determine
-  //  orientation
-
-  if (e.is_degenerate ()) {
-    return false;
-  }
-
   db::Edge g (other);
-  int s1 = e.side_of (g.p1 ());
-  int s2 = e.side_of (g.p2 ());
+
+  //  s1 = side of g.p1 wrt e
+  //  s2 = side of g.p2 wrt e
+  int s1, s2;
+  if (e.is_degenerate ()) {
+    if (g.contains (e.p1 ())) {
+      s1 = s2 = 0;
+    } else {
+      s1 = s2 = -1;
+    }
+  } else {
+    s1 = e.side_of (g.p1 ());
+    s2 = e.side_of (g.p2 ());
+  }
 
   bool include_zero = include_zero_flag (zd_mode, e, g);
   int thr = include_zero ? 0 : -1;
@@ -259,37 +289,53 @@ static bool var_near_part_of_edge (zero_distance_mode zd_mode, db::coord_traits<
   //  Handle the case of point vs. edge
 
   if (g.is_degenerate ()) {
-    if (e.side_of (g.p1 ()) > thr) {
-      return false;
-    }
-    if (double (e.distance (g.p1 ())) <= -double (d)) {
-      return false;
-    }
-    if (db::sprod (db::Vector (g.p1 () - e.p1 ()), e.d ()) < -(dd * e.double_length ())) {
-      return false;
-    }
-    if (db::sprod (db::Vector (e.p2 () - g.p1 ()), e.d ()) < -(dd * e.double_length ())) {
-      return false;
+
+    if (! e.is_degenerate ()) {
+      if (e.side_of (g.p1 ()) > thr) {
+        return false;
+      }
+      if (db::sprod (db::Vector (g.p1 () - e.p1 ()), e.d ()) < -(dd * e.double_length ())) {
+        return false;
+      }
+      if (db::sprod (db::Vector (e.p2 () - g.p1 ()), e.d ()) < -(dd * e.double_length ())) {
+        return false;
+      }
+      if (double (e.distance (g.p1 ())) <= -double (d)) {
+        return false;
+      }
+    } else {
+      //  point to point
+      if (e.p1 ().distance (g.p1 ()) >= double (d)) {
+        return false;
+      }
     }
+
     if (output) {
       *output = g;
     }
     return true;
+
   }
 
   //  Determine body interactions (projected mode)
 
-  double l1 = std::numeric_limits<double>::min (), l2 = std::numeric_limits<double>::max ();
+  double l1 = std::numeric_limits<double>::lowest (), l2 = std::numeric_limits<double>::max ();
 
-  double ef = 1.0 / e.double_length ();
-  db::DVector ep = db::DVector (ef * e.dx (), ef * e.dy ());
-  db::DVector en = db::DVector (ef * e.dy (), -ef * e.dx ());
+  db::DVector ep, en;
+  double ef = 0.0;
+  if (! e.is_degenerate ()) {
+    ef = 1.0 / e.double_length ();
+    ep = db::DVector (ef * e.dx (), ef * e.dy ());
+    en = db::DVector (ef * e.dy (), -ef * e.dx ());
+  }
 
   //  handle the parallel case
   if (e.parallel (g)) {
+
     if (std::abs (double (e.distance (g.p1 ()))) >= double (d)) {
       return false;
     }
+
   } else {
 
     db::DPoint e1d = db::DPoint (e.p1 ()) + en * double (d);
@@ -307,10 +353,21 @@ static bool var_near_part_of_edge (zero_distance_mode zd_mode, db::coord_traits<
   }
 
   if (db::sprod_sign (e, g) == 0) {
-    if (db::sprod (db::Vector (g.p1 () - e.p1 ()), e.d ()) < -(dd * e.double_length ()) ||
-        db::sprod (db::Vector (e.p2 () - g.p1 ()), e.d ()) < -(dd * e.double_length ())) {
-      return false;
+
+    if (! g.is_degenerate ()) {
+
+      if (db::sprod (db::Vector (g.p1 () - e.p1 ()), e.d ()) < -(dd * e.double_length ()) ||
+          db::sprod (db::Vector (e.p2 () - g.p1 ()), e.d ()) < -(dd * e.double_length ())) {
+        return false;
+      }
+
+      double l = db::sprod (db::DVector (e.p1 () - g.p1 ()), db::DVector (g.d ())) / g.double_sq_length ();
+      double dl = double (dd) / g.double_length ();
+      l1 = l - dl;
+      l2 = l + dl;
+
     }
+
   } else {
 
     double det = db::vprod (db::DVector (g.d ()), en);
@@ -410,7 +467,9 @@ EdgeRelationFilter::check (const db::Edge &a, const db::Edge &b, db::EdgePair *o
 
   //  Check whether the edges have an angle less than the ignore_angle parameter
 
-  if (m_ignore_angle == 90.0) {
+  if (a.is_degenerate () || b.is_degenerate ()) {
+    //  accept dots as "always good"
+  } else if (m_ignore_angle == 90.0) {
     if (db::sprod_sign (aa, b) >= 0) {
       return false;
     }
diff --git a/src/drc/unit_tests/drcSimpleTests.cc b/src/drc/unit_tests/drcSimpleTests.cc
index 85547ab6b..258c5969d 100644
--- a/src/drc/unit_tests/drcSimpleTests.cc
+++ b/src/drc/unit_tests/drcSimpleTests.cc
@@ -2055,3 +2055,14 @@ TEST(145d_edges_merge)
   run_test (_this, "145", true);
 }
 
+//  issue 2141
+TEST(146_edges_and_corners)
+{
+  run_test (_this, "146", false);
+}
+
+TEST(146d_edges_and_corners)
+{
+  run_test (_this, "146", true);
+}
+
diff --git a/testdata/drc/drcSimpleTests_146.drc b/testdata/drc/drcSimpleTests_146.drc
new file mode 100644
index 000000000..b52cb8548
--- /dev/null
+++ b/testdata/drc/drcSimpleTests_146.drc
@@ -0,0 +1,51 @@
+
+source $drc_test_source
+target $drc_test_target
+
+if $drc_test_deep
+  deep
+end
+
+l1 = input(1, 0)
+l2 = input(2, 0)
+
+l1.output(1, 0)
+l2.output(2, 0)
+l1e = l1.edges
+l2e = l2.edges
+l1c = l1.corners(as_dots)
+l2c = l2.corners(as_dots)
+
+l1e.sep(l2c, 0.6).output(100, 0)
+l1c.sep(l2e, 0.6).output(101, 0)
+l1c.sep(l2c, 0.6).output(102, 0)
+l1e.enc(l2c, 0.6).output(103, 0)
+l1c.enc(l2e, 0.6).output(104, 0)
+l1c.enc(l2c, 0.6).output(105, 0)
+l2e.width(1.0).output(106, 0)
+l2c.width(1.0).output(107, 0)
+l2e.space(2.0).output(108, 0)
+l2c.space(2.0).output(109, 0)
+
+l1e.sep(l2c, 0.6, square).output(110, 0)
+l1c.sep(l2e, 0.6, square).output(111, 0)
+l1c.sep(l2c, 0.6, square).output(112, 0)
+l1e.enc(l2c, 0.6, square).output(113, 0)
+l1c.enc(l2e, 0.6, square).output(114, 0)
+l1c.enc(l2c, 0.6, square).output(115, 0)
+l2e.width(1.0, square).output(116, 0)
+l2c.width(1.0, square).output(117, 0)
+l2e.space(2.0, square).output(118, 0)
+l2c.space(2.0, square).output(119, 0)
+
+l1e.sep(l2c, 0.6, projection).output(120, 0)
+l1c.sep(l2e, 0.6, projection).output(121, 0)
+l1c.sep(l2c, 0.6, projection).output(122, 0)
+l1e.enc(l2c, 0.6, projection).output(123, 0)
+l1c.enc(l2e, 0.6, projection).output(124, 0)
+l1c.enc(l2c, 0.6, projection).output(125, 0)
+l2e.width(1.0, projection).output(126, 0)
+l2c.width(1.0, projection).output(127, 0)
+l2e.space(2.0, projection).output(128, 0)
+l2c.space(2.0, projection).output(129, 0)
+
diff --git a/testdata/drc/drcSimpleTests_146.gds b/testdata/drc/drcSimpleTests_146.gds
new file mode 100644
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HcmV?d00001

diff --git a/testdata/drc/drcSimpleTests_au146d.gds b/testdata/drc/drcSimpleTests_au146d.gds
new file mode 100644
index 0000000000000000000000000000000000000000..8621421d653e54fb6efaa41ea90a9c9f53ee2d1f
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literal 0
HcmV?d00001


From a9d52b7a70b746137ca6cd477c3903c5382ad59c Mon Sep 17 00:00:00 2001
From: Matthias Koefferlein <matthias@klayout.de>
Date: Fri, 5 Sep 2025 08:05:27 +0200
Subject: [PATCH 3/4] Fixing case of point vs. edge in projecting mode

---
 src/db/db/dbEdgePairRelations.cc       |   3 ++-
 testdata/drc/drcSimpleTests_au146.gds  | Bin 7546 -> 7930 bytes
 testdata/drc/drcSimpleTests_au146d.gds | Bin 8910 -> 9294 bytes
 3 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/db/db/dbEdgePairRelations.cc b/src/db/db/dbEdgePairRelations.cc
index 5d32bcc27..de4f46078 100644
--- a/src/db/db/dbEdgePairRelations.cc
+++ b/src/db/db/dbEdgePairRelations.cc
@@ -330,6 +330,7 @@ static bool var_near_part_of_edge (zero_distance_mode zd_mode, db::coord_traits<
   }
 
   //  handle the parallel case
+  //  NOTE: a point is "parallel" to an edge
   if (e.parallel (g)) {
 
     if (std::abs (double (e.distance (g.p1 ()))) >= double (d)) {
@@ -387,7 +388,7 @@ static bool var_near_part_of_edge (zero_distance_mode zd_mode, db::coord_traits<
   l1 = std::max (0.0, l1);
   l2 = std::min (1.0, l2);
 
-  if (l1 >= l2) {
+  if (l1 > l2 + db::epsilon) {
     return false;
   } else {
     if (output) {
diff --git a/testdata/drc/drcSimpleTests_au146.gds b/testdata/drc/drcSimpleTests_au146.gds
index 66262fc23a950bd571f55429ba6cf32ffdf6c9b7..d85bb1933ae7815c9da5a0f5f58d47d1fe5744ac 100644
GIT binary patch
delta 459
zcmZvYJr05}7>3_gsHo9s8kn3&oWu)|cn{-AOdJ|_6C@sicmU&~qepS{3QYDFN^pAM
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sdF6Ky=qzYtd6-<}SE?nJYOS67KcVB3wYgkTd1TX4P3*k&AFt%ieg<zV-T(jq

delta 75
zcmexm`^!p+fsKKQDS|<Uk%|2!11AFugE)gUgBdb=qLQjG7U7Li4@D>M7HimSEwP^s
E0N?BmMF0Q*

diff --git a/testdata/drc/drcSimpleTests_au146d.gds b/testdata/drc/drcSimpleTests_au146d.gds
index 8621421d653e54fb6efaa41ea90a9c9f53ee2d1f..7ea9e5329918294c7d7637c7f741075eb3000fbe 100644
GIT binary patch
delta 508
zcmZvZI|>3p42J(5bsvhN*jNZYz|I4B0m0HzJc+Q%Vq-5`ig!>fyoI%eU~MhhD8__g
za7MQJhCh6hker66Q5QaxnxN^a;D!hVgz!+e-|KF#o)Pb-*D#sEuP6ZhY7WS?fWk#H
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delta 124
zcmX@-an4nVfsKKQDS|<Uk%|2!11AFugE)gUgBdb=qLQjG7U7Li_c<o-<ZPI1$=!lY
Re)9$H$$VHP%A{^^0ssvP6_5Y`


From 90ed8a2390e282711a1a2a96f86c31c4943c58be Mon Sep 17 00:00:00 2001
From: Matthias Koefferlein <matthias@klayout.de>
Date: Fri, 5 Sep 2025 23:48:49 +0200
Subject: [PATCH 4/4] Excluding degenerated edges from polygons so we don't
 consider them corners, addressing duplicate corners with zero distance.

---
 src/db/db/dbEdgePairRelations.cc              | 13 +++++++++++--
 src/db/db/dbRegionCheckUtils.cc               |  8 +++++---
 src/db/unit_tests/dbEdgePairRelationsTests.cc | 10 ++++++----
 3 files changed, 22 insertions(+), 9 deletions(-)

diff --git a/src/db/db/dbEdgePairRelations.cc b/src/db/db/dbEdgePairRelations.cc
index de4f46078..e5da82d64 100644
--- a/src/db/db/dbEdgePairRelations.cc
+++ b/src/db/db/dbEdgePairRelations.cc
@@ -353,6 +353,8 @@ static bool var_near_part_of_edge (zero_distance_mode zd_mode, db::coord_traits<
 
   }
 
+  bool allow_zero_projection = false;
+
   if (db::sprod_sign (e, g) == 0) {
 
     if (! g.is_degenerate ()) {
@@ -367,6 +369,8 @@ static bool var_near_part_of_edge (zero_distance_mode zd_mode, db::coord_traits<
       l1 = l - dl;
       l2 = l + dl;
 
+      allow_zero_projection = true;
+
     }
 
   } else {
@@ -388,7 +392,7 @@ static bool var_near_part_of_edge (zero_distance_mode zd_mode, db::coord_traits<
   l1 = std::max (0.0, l1);
   l2 = std::min (1.0, l2);
 
-  if (l1 > l2 + db::epsilon) {
+  if (allow_zero_projection ? l1 > l2 + db::epsilon : l1 > l2 - db::epsilon) {
     return false;
   } else {
     if (output) {
@@ -469,7 +473,12 @@ EdgeRelationFilter::check (const db::Edge &a, const db::Edge &b, db::EdgePair *o
   //  Check whether the edges have an angle less than the ignore_angle parameter
 
   if (a.is_degenerate () || b.is_degenerate ()) {
-    //  accept dots as "always good"
+    //  accept dots as "always good", expect if they are identical and the zero distance mode does not include this case
+    if (a == b && (m_zero_distance_mode == NeverIncludeZeroDistance ||
+                   m_zero_distance_mode == IncludeZeroDistanceWhenCollinearAndTouching ||
+                   m_zero_distance_mode == IncludeZeroDistanceWhenOverlapping)) {
+      return false;
+    }
   } else if (m_ignore_angle == 90.0) {
     if (db::sprod_sign (aa, b) >= 0) {
       return false;
diff --git a/src/db/db/dbRegionCheckUtils.cc b/src/db/db/dbRegionCheckUtils.cc
index f57ef287e..7f71edb4c 100644
--- a/src/db/db/dbRegionCheckUtils.cc
+++ b/src/db/db/dbRegionCheckUtils.cc
@@ -463,8 +463,10 @@ void
 poly2poly_check<PolygonType>::enter (const PolygonType &o, size_t p)
 {
   for (typename PolygonType::polygon_edge_iterator e = o.begin_edge (); ! e.at_end (); ++e) {
-    m_edge_heap.push_back (*e);
-    m_scanner.insert (& m_edge_heap.back (), p);
+    if (! (*e).is_degenerate ()) {
+      m_edge_heap.push_back (*e);
+      m_scanner.insert (& m_edge_heap.back (), p);
+    }
   }
 }
 
@@ -497,7 +499,7 @@ poly2poly_check<PolygonType>::enter (const PolygonType &o, size_t p, const poly2
   }
 
   for (typename PolygonType::polygon_edge_iterator e = o.begin_edge (); ! e.at_end (); ++e) {
-    if (interact (box, *e)) {
+    if (! (*e).is_degenerate () && interact (box, *e)) {
       m_edge_heap.push_back (*e);
       m_scanner.insert (& m_edge_heap.back (), p);
     }
diff --git a/src/db/unit_tests/dbEdgePairRelationsTests.cc b/src/db/unit_tests/dbEdgePairRelationsTests.cc
index 42bc669d3..c0809bbda 100644
--- a/src/db/unit_tests/dbEdgePairRelationsTests.cc
+++ b/src/db/unit_tests/dbEdgePairRelationsTests.cc
@@ -135,7 +135,8 @@ TEST(3)
   EXPECT_EQ (output.to_string (), "(80,0;-60,-100)");
   EXPECT_EQ (square_near_part_of_edge (db::AlwaysIncludeZeroDistance, 100, db::Edge (db::Point (0, 0), db::Point (100, 0)), db::Edge (db::Point (-100, 200), db::Point (-100, -200)), &output), true);
   EXPECT_EQ (output.to_string (), "(-100,0;-100,-100)");
-  EXPECT_EQ (square_near_part_of_edge (db::AlwaysIncludeZeroDistance, 100, db::Edge (), db::Edge (db::Point (-100, 200), db::Point (-100, -200)), &output), false);
+  EXPECT_EQ (square_near_part_of_edge (db::AlwaysIncludeZeroDistance, 100, db::Edge (), db::Edge (db::Point (-100, 200), db::Point (-100, -200)), &output), true);
+  EXPECT_EQ (output.to_string (), "(-100,100;-100,-100)");   //  dot vs. line (issue #2141)
   EXPECT_EQ (square_near_part_of_edge (db::AlwaysIncludeZeroDistance, 100, db::Edge (db::Point (0, 0), db::Point (100, 0)), db::Edge (db::Point (100, 50), db::Point (100, 50)), &output), false);
   EXPECT_EQ (square_near_part_of_edge (db::AlwaysIncludeZeroDistance, 100, db::Edge (db::Point (0, 0), db::Point (100, 0)), db::Edge (db::Point (100, -50), db::Point (100, -50)), &output), true);
   EXPECT_EQ (output.to_string (), "(100,-50;100,-50)");
@@ -170,14 +171,15 @@ TEST(4)
   EXPECT_EQ (projected_near_part_of_edge (db::AlwaysIncludeZeroDistance, 100, db::Edge (db::Point (0, 0), db::Point (100, 0)), db::Edge (db::Point (0, 200), db::Point (200, -200)), &output), false);
   EXPECT_EQ (projected_near_part_of_edge (db::AlwaysIncludeZeroDistance, 100, db::Edge (db::Point (0, 0), db::Point (100, 0)), db::Edge (db::Point (120, 200), db::Point (120, -200)), &output), false);
   EXPECT_EQ (projected_near_part_of_edge (db::AlwaysIncludeZeroDistance, 100, db::Edge (db::Point (0, 0), db::Point (100, 0)), db::Edge (db::Point (100, 200), db::Point (100, -200)), &output), true);
-  EXPECT_EQ (output.to_string (), "(100,0;100,-100)");
+  EXPECT_EQ (output.to_string (), "(100,0;100,0)");
   EXPECT_EQ (projected_near_part_of_edge (db::AlwaysIncludeZeroDistance, 100, db::Edge (db::Point (0, 0), db::Point (100, 0)), db::Edge (db::Point (80, 200), db::Point (80, -200)), &output), true);
-  EXPECT_EQ (output.to_string (), "(80,0;80,-100)");
+  EXPECT_EQ (output.to_string (), "(80,0;80,0)");
   EXPECT_EQ (projected_near_part_of_edge (db::AlwaysIncludeZeroDistance, 100, db::Edge (db::Point (0, 0), db::Point (100, 0)), db::Edge (db::Point (-80, 200), db::Point (-80, -200)), &output), false);
   EXPECT_EQ (projected_near_part_of_edge (db::AlwaysIncludeZeroDistance, 100, db::Edge (db::Point (0, 0), db::Point (100, 0)), db::Edge (db::Point (80, 0), db::Point (-200, -200)), &output), true);
   EXPECT_EQ (output.to_string (), "(80,0;0,-57)");
   EXPECT_EQ (projected_near_part_of_edge (db::AlwaysIncludeZeroDistance, 100, db::Edge (db::Point (0, 0), db::Point (100, 0)), db::Edge (db::Point (-100, 200), db::Point (-100, -200)), &output), false);
-  EXPECT_EQ (projected_near_part_of_edge (db::AlwaysIncludeZeroDistance, 100, db::Edge (), db::Edge (db::Point (-100, 200), db::Point (-100, -200)), &output), false);
+  EXPECT_EQ (projected_near_part_of_edge (db::AlwaysIncludeZeroDistance, 100, db::Edge (), db::Edge (db::Point (-100, 200), db::Point (-100, -200)), &output), true);
+  EXPECT_EQ (output.to_string (), "(-100,0;-100,0)");  //  dot vs. line (issue #2141)
   EXPECT_EQ (projected_near_part_of_edge (db::AlwaysIncludeZeroDistance, 100, db::Edge (db::Point (0, 0), db::Point (100, 0)), db::Edge (db::Point (100, 50), db::Point (100, 50)), &output), false);
   EXPECT_EQ (projected_near_part_of_edge (db::AlwaysIncludeZeroDistance, 100, db::Edge (db::Point (0, 0), db::Point (100, 0)), db::Edge (db::Point (100, -50), db::Point (100, -50)), &output), true);
   EXPECT_EQ (output.to_string (), "(100,-50;100,-50)");