Fix invalid MD interpolation for wells starting at zero depth.

The interpolation procedure adds a point at zero depth. If the well already
had a starting point there the interpolation would set all MD values to zero.
Fixed by adding the zero point only when necessary.

ApplicationCode/ReservoirDataModel/RigWellPathGeometryTools.cpp

@@ -322,9 +322,10 @@ QwtSpline RigWellPathGeometryTools::createSpline( const std::vector<double>& ori
     QwtSplineCurveFitter curveFitter;
     QPolygonF            splinePoints = curveFitter.fitCurve( polygon );
 
-    // Extend spline from 0.0 to a large value for MD
+    // Extend spline from 0.0 (if it does not already exist) to a large value for MD
     // This is to force a specific and known extrapolation.
     // Otherwise we get an undefined and unknown extrapolation.
+    if ( !( splinePoints[0].x() == 0.0 && splinePoints[0].y() == 0.0 ) )
     {
         double x1 = splinePoints[0].x();
         double x2 = splinePoints[1].x();

ApplicationCode/UnitTests/RigWellPathGeometryTools-Test.cpp

@@ -59,6 +59,21 @@ TEST( RigWellPathGeometryTools, LinearPath )
     }
 }
 
+TEST( RigWellPathGeometryTools, LinearPathStartingAtZero )
+{
+    std::vector<double> mdValues      = {0, 100, 500, 1000};
+    std::vector<double> tvdValues     = {0, 50, 250, 500};
+    std::vector<double> fullTVDValues = {0, 50, 100, 150, 200, 250, 300, 350, 400, 450, 500};
+
+    std::vector<double> fullMDValues = RigWellPathGeometryTools::interpolateMdFromTvd( mdValues, tvdValues, fullTVDValues );
+
+    EXPECT_EQ( fullTVDValues.size(), fullMDValues.size() );
+    for ( size_t i = 0; i < fullTVDValues.size(); ++i )
+    {
+        EXPECT_NEAR( 2.0 * fullTVDValues[i], fullMDValues[i], TOLERANCE );
+    }
+}
+
 double quadraticFunction( double x )
 {
     return 0.0015 * std::pow( x, 2 ) - 0.25 * x + 100;