acute angle between two straight lines

jmeidow · jmeidow · commit 8afebae8fa28 · 2026-01-12T09:32:19.000+01:00
diff --git a/src/geometry/acute.h b/src/geometry/acute.h
@@ -0,0 +1,63 @@
+/*
+ * This file is part of the GreasePad distribution (https://github.com/FraunhoferIOSB/GreasePad).
+ * Copyright (c) 2022-2026 Jochen Meidow, Fraunhofer IOSB
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#ifndef ACUTE_H
+#define ACUTE_H
+
+
+#include <Eigen/Core>
+
+#include <cassert>
+#include <cfloat>
+#include <cmath>
+#include <cstdlib>
+
+
+namespace Geometry {
+
+using Eigen::Vector2d;
+using Eigen::Vector3d;
+
+
+//! acute angle between two straight lines in radians
+static inline double acute( const Vector3d l, const Vector3d m)
+{
+    constexpr double pi   = 3.141592653589793;
+    constexpr double pi_2 = 3.141592653589793/2;
+
+    Vector2d lh = l.head(2);
+    Vector2d mh = m.head(2);
+    assert( lh.norm() > FLT_EPSILON );
+    assert( mh.norm() > FLT_EPSILON );
+    lh.normalize();
+    mh.normalize();
+
+    assert( std::fabs(lh.dot(mh)) <= 1.0 );  // a'*b in [-1,+1]
+    double alpha = std::acos( lh.dot(mh) );  // [0,pi]
+    if ( alpha > pi_2) {
+        alpha = pi -alpha;
+    }
+    assert( alpha >= 0.0    );
+    assert( alpha <= pi_2 );
+
+    return alpha;
+}
+
+} // namespace Geometry
+
+#endif // ACUTE_H
diff --git a/src/greasepad.pro b/src/greasepad.pro
@@ -51,6 +51,7 @@ HEADERS += \
     conncomp.h \
     constraints.h \
     geometry/aabb.h \
+    geometry/acute.h \
     geometry/conics.h \
     geometry/minrot.h \
     geometry/skew.h \
diff --git a/src/state.cpp b/src/state.cpp
@@ -35,6 +35,7 @@
 #include "adjustment.h"
 #include "conncomp.h"
 #include "constraints.h"
+#include "geometry/acute.h"
 #include "global.h"
 #include "mainscene.h"
 #include "matfun.h"
@@ -892,15 +893,16 @@ bool impl::are_orthogonal( const Index a,
 bool impl::are_identical( const Index a,
                           const Index b)
 {
-    // pre-check with acute angle
-    const double alpha = m_segm.at(a)->ul().acute( m_segm.at(b)->ul() );
-    constexpr double rho = 180./3.14159;
+    // (1) pre-check with acute angle
+    const double alpha = Geometry::acute( m_segm.at(a)->ul().v(),
+                                          m_segm.at(b)->ul().v() );
+    constexpr double rho = 180./3.141592653589793; // = 180°/pi = 57.2958°
     constexpr double T_deg_pre_check = 20.0;
-    if ( alpha*rho > T_deg_pre_check ) {  // 180°/pi = 57.2958°
+    if ( alpha*rho > T_deg_pre_check ) {
         return false;
     }
 
-    // statistical test
+    // (2) statistical test
     return  m_segm.at(a)->straightLineIsIdenticalTo( m_segm.at(b)->ul(),
                                                      State::recogn_.quantile_chi2_2dof() );
 }
diff --git a/src/ustraightline.cpp b/src/ustraightline.cpp
@@ -1,6 +1,6 @@
 /*
  * This file is part of the GreasePad distribution (https://github.com/FraunhoferIOSB/GreasePad).
- * Copyright (c) 2022-2025 Jochen Meidow, Fraunhofer IOSB
+ * Copyright (c) 2022-2026 Jochen Meidow, Fraunhofer IOSB
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -152,28 +152,6 @@ uPoint uStraightLine::project(const uPoint &ux) const
 }
 
 
-
-double uStraightLine::acute(const uStraightLine &um) const
-{
-    Eigen::Vector2d a = v().head(2);
-    Eigen::Vector2d b = um.v().head(2);
-    assert( a.norm() > FLT_EPSILON );
-    assert( b.norm() > FLT_EPSILON );
-    a.normalize();
-    b.normalize();
-
-    assert( fabs(a.dot(b)) <= 1.0 );  // a'*b in [-1,+1]
-    double alpha = acos( a.dot(b) );  // [0,pi]
-    if ( alpha > M_PI_2) {            // M_PI_2 = pi/2
-        alpha = M_PI -alpha;
-    }
-    assert( alpha >= 0.0    );
-    assert( alpha <= M_PI_2 );
-    return alpha;
-}
-
-
-
 //! Get Euclidean normalized version of this uncertain straight line
 uStraightLine uStraightLine::euclidean() const
 {
diff --git a/src/ustraightline.h b/src/ustraightline.h
@@ -1,6 +1,6 @@
 /*
  * This file is part of the GreasePad distribution (https://github.com/FraunhoferIOSB/GreasePad).
- * Copyright (c) 2022-2025 Jochen Meidow, Fraunhofer IOSB
+ * Copyright (c) 2022-2026 Jochen Meidow, Fraunhofer IOSB
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -54,8 +54,8 @@ class uStraightLine : public BasicEntity2D
     //! Signed distance between (0,0) and this straight line
     [[nodiscard]] double signedDistanceToOrigin() const { return v()(2)/v().head(2).norm(); }
 
+    //! Project point onto straight line
     [[nodiscard]] uPoint project( const uPoint & ux) const;
-    [[nodiscard]] double acute(   const uStraightLine & um ) const;
 
     // unary relations ..................................................
     [[nodiscard]] bool isVertical(   double T) const;
