Added function to get Y value for a point on a line segment

src/openalpr/utility.cpp

@@ -439,6 +439,12 @@ int levenshteinDistance (const std::string &s1, const std::string &s2, int max)
     return slope * (x - p2.x) + p2.y;
   }
 
+  float LineSegment::getXPointAt(float y)
+  {
+    float y_intercept = getPointAt(0);
+    return (y - y_intercept) / slope;
+  }
+  
   Point LineSegment::closestPointOnSegmentTo(Point p)
   {
     float top = (p.x - p1.x) * (p2.x - p1.x) + (p.y - p1.y)*(p2.y - p1.y);

src/openalpr/utility.h

@@ -55,6 +55,7 @@ namespace alpr
       bool isPointBelowLine(cv::Point tp);
 
       float getPointAt(float x);
+      float getXPointAt(float y);
 
       cv::Point closestPointOnSegmentTo(cv::Point p);
 

src/tests/test_utility.cpp

@@ -26,6 +26,11 @@ TEST_CASE( "LineSegment Test", "[2d primitives]" ) {
   REQUIRE( flat_horizontal.midpoint().x == 11 );
   REQUIRE( flat_horizontal.getPointAt(11) == 1 );
   
+  LineSegment rising_45(1,1, 5,5);
+  
+  REQUIRE( rising_45.getPointAt(3) == 3 );
+  REQUIRE( rising_45.getXPointAt(3) == 3 );
+  
   // Test distance between points calculation
   REQUIRE( distanceBetweenPoints(Point(10,10), Point(20,20)) == Approx(14.1421) );
   REQUIRE( distanceBetweenPoints(Point(-5,10), Point(20,-12)) == Approx(33.3017) );