Sub: Add missing terrain.cpp file

ArduSub/terrain.cpp

@@ -0,0 +1,40 @@
+/// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*-
+
+#include "Sub.h"
+
+// update terrain data
+void Sub::terrain_update()
+{
+#if AP_TERRAIN_AVAILABLE && AC_TERRAIN
+    terrain.update();
+
+    // tell the rangefinder our height, so it can go into power saving
+    // mode if available
+#if CONFIG_SONAR == ENABLED
+    float height;
+    if (terrain.height_above_terrain(height, true)) {
+        sonar.set_estimated_terrain_height(height);
+    }
+#endif
+#endif
+}
+
+// log terrain data - should be called at 1hz
+void Sub::terrain_logging()
+{
+#if AP_TERRAIN_AVAILABLE && AC_TERRAIN
+    if (should_log(MASK_LOG_GPS)) {
+        terrain.log_terrain_data(DataFlash);
+    }
+#endif
+}
+
+// should we use terrain data for things including the home altitude
+bool Sub::terrain_use()
+{
+#if AP_TERRAIN_AVAILABLE && AC_TERRAIN
+    return (g.terrain_follow > 0);
+#else
+    return false;
+#endif
+}