refs #852 Use X-Plane terrain probe to provide ground elevation to the interpolator.

src/xbus/terrainprobe.h

@@ -0,0 +1,39 @@
+/* Copyright (C) 2017
+ * swift Project Community / Contributors
+ *
+ * This file is part of swift project. It is subject to the license terms in the LICENSE file found in the top-level
+ * directory of this distribution and at http://www.swift-project.org/license.html. No part of swift project,
+ * including this file, may be copied, modified, propagated, or distributed except according to the terms
+ * contained in the LICENSE file.
+ */
+
+#ifndef BLACKSIM_XBUS_ELEVATIONPROVIDER_H
+#define BLACKSIM_XBUS_ELEVATIONPROVIDER_H
+
+#include <XPLM/XPLMScenery.h>
+
+namespace XBus
+{
+    /*!
+     * Class based interface to X-Plane SDK terrain probe.
+     */
+    class CTerrainProbe
+    {
+    public:
+        //! Constructor.
+        CTerrainProbe();
+
+        //! Destructor;
+        ~CTerrainProbe();
+
+        //! Get the elevation in meters at the given point in OpenGL space.
+        //! \note Due to the Earth's curvature, the OpenGL vertical axis may not be exactly perpendicular to the surface of the geoid.
+        //! \return NaN if no ground was detected.
+        double getElevation(double degreesLatitude, double degreesLongitude, double metersAltitude) const;
+
+    private:
+        XPLMProbeRef m_ref = nullptr;
+    };
+}
+
+#endif