Add elevationAtLocation determination in the Globe.

Calculate correct GL near clip distance and limit Navigator to avoid terrain collisions.
Fix lookAt point calculation for gesture begin - take terrain altitude in consideration.
Add terrain elevation output into example application.
Navigator tests were commented as it is now dependent on context.

Author: EMaksymenko

worldwind-examples/src/main/java/gov/nasa/worldwindx/GeneralGlobeActivity.java

@@ -29,6 +29,7 @@ public class GeneralGlobeActivity extends BasicGlobeActivity {
     // UI elements
     protected TextView latView;
     protected TextView lonView;
+    protected TextView elevView;
     protected TextView altView;
     protected ImageView crosshairs;
     protected ViewGroup overlay;
@@ -60,6 +61,7 @@ protected void onCreate(Bundle savedInstanceState) {
         this.overlay.setVisibility(View.VISIBLE);
         this.latView = (TextView) findViewById(R.id.lat_value);
         this.lonView = (TextView) findViewById(R.id.lon_value);
+        this.elevView = (TextView) findViewById(R.id.elev_value);
         this.altView = (TextView) findViewById(R.id.alt_value);
         ObjectAnimator fadeOut = ObjectAnimator.ofFloat(this.crosshairs, "alpha", 0f).setDuration(1500);
         fadeOut.setStartDelay((long) 500);
@@ -135,6 +137,7 @@ protected void fadeCrosshairs() {
     protected void updateOverlayContents(LookAt lookAt, Camera camera) {
         latView.setText(formatLatitude(lookAt.latitude));
         lonView.setText(formatLongitude(lookAt.longitude));
+        elevView.setText(formatElevaton(wwd.getGlobe().getElevationAtLocation(lookAt.latitude, lookAt.longitude)));
         altView.setText(formatAltitude(camera.altitude));
     }
 
@@ -147,6 +150,7 @@ protected void updateOverlayColor(@WorldWind.NavigatorAction int eventAction) {
         int color = (eventAction == WorldWind.NAVIGATOR_STOPPED) ? 0xA0FFFF00 /*semi-transparent yellow*/ : Color.YELLOW;
         latView.setTextColor(color);
         lonView.setTextColor(color);
+        elevView.setTextColor(color);
         altView.setTextColor(color);
     }
 
@@ -160,6 +164,12 @@ protected String formatLongitude(double longitude) {
         return String.format("%7.3f°%s", (longitude * sign), (sign >= 0.0 ? "E" : "W"));
     }
 
+    protected String formatElevaton(double elevation) {
+        return String.format("Alt: %,.0f %s",
+                (elevation < 100000 ? elevation : elevation / 1000),
+                (elevation < 100000 ? "m" : "km"));
+    }
+
     protected String formatAltitude(double altitude) {
         return String.format("Eye: %,.0f %s",
             (altitude < 100000 ? altitude : altitude / 1000),

worldwind-examples/src/main/res/layout/globe_content.xml

@@ -82,6 +82,23 @@
             android:padding="10dp"
             android:text="@string/spacer"/>
 
+        <TextView
+            android:id="@+id/elev_value"
+            android:layout_width="wrap_content"
+            android:layout_height="wrap_content"
+            android:shadowColor="#000000"
+            android:shadowRadius="2"
+            android:shadowDx="0"
+            android:shadowDy="0"
+            android:singleLine="true"/>
+
+        <TextView
+            android:id="@+id/spacer3"
+            android:layout_width="wrap_content"
+            android:layout_height="wrap_content"
+            android:padding="10dp"
+            android:text="@string/spacer"/>
+
         <TextView
             android:id="@+id/alt_value"
             android:layout_width="wrap_content"

worldwind/src/main/java/gov/nasa/worldwind/BasicFrameController.java

@@ -65,7 +65,6 @@ protected void renderTerrainPickedObject(RenderContext rc) {
         // picked object ID and the intersection position.
         if (rc.pickRay != null && rc.terrain.intersect(rc.pickRay, this.pickPoint)) {
             rc.globe.cartesianToGeographic(this.pickPoint.x, this.pickPoint.y, this.pickPoint.z, this.pickPos);
-            this.pickPos.altitude = 0; // report the actual altitude, which may not lie on the terrain's surface
             rc.offerPickedObject(PickedObject.fromTerrain(pickedObjectId, this.pickPos));
         }
     }

worldwind/src/main/java/gov/nasa/worldwind/Navigator.java

@@ -28,19 +28,29 @@ public class Navigator {
 
     protected double roll;
 
-    private Camera scratchCamera = new Camera();
+    private final Camera scratchCamera = new Camera();
 
-    private Matrix4 modelview = new Matrix4();
+    private final Matrix4 modelview = new Matrix4();
 
-    private Matrix4 origin = new Matrix4();
+    private final Matrix4 origin = new Matrix4();
 
-    private Vec3 originPoint = new Vec3();
+    private final Vec3 originPoint = new Vec3();
 
-    private Position originPos = new Position();
+    private final Position originPos = new Position();
 
-    private Line forwardRay = new Line();
+    private final Line forwardRay = new Line();
 
-    public Navigator() {
+    private final WorldWindow wwd;
+
+    private final static double COLLISION_THRESHOLD = 10.0; // 10m above surface
+
+    public Navigator(WorldWindow wwd) {
+        if (wwd == null) {
+            throw new IllegalArgumentException(
+                    Logger.logMessage(Logger.ERROR, "Navigator", "constructor", "missingWorldWindow"));
+        }
+
+        this.wwd = wwd;
     }
 
     public double getLatitude() {
@@ -193,16 +203,23 @@ public Matrix4 getAsViewingMatrix(Globe globe, Matrix4 result) {
 
     protected LookAt cameraToLookAt(Globe globe, Camera camera, LookAt result) {
         this.cameraToViewingMatrix(globe, camera, this.modelview);
-        this.modelview.extractEyePoint(this.forwardRay.origin);
-        this.modelview.extractForwardVector(this.forwardRay.direction);
 
-        if (!globe.intersect(this.forwardRay, this.originPoint)) {
-            double horizon = globe.horizonDistance(camera.altitude);
-            this.forwardRay.pointAt(horizon, this.originPoint);
+        // Pick terrain located behind the viewport center point
+        PickedObject terrainPickedObject = wwd.pick(wwd.getViewport().width / 2f, wwd.getViewport().height / 2f).terrainPickedObject();
+        if (terrainPickedObject != null) {
+            // Use picked terrain position including approximate rendered altitude
+            this.originPos.set(terrainPickedObject.getTerrainPosition());
+            globe.geographicToCartesian(this.originPos.latitude, this.originPos.longitude, this.originPos.altitude, this.originPoint);
+            globe.cartesianToLocalTransform(this.originPoint.x, this.originPoint.y, this.originPoint.z, this.origin);
+        } else {
+            // Center is outside the globe - use point on horizon
+            this.modelview.extractEyePoint(this.forwardRay.origin);
+            this.modelview.extractForwardVector(this.forwardRay.direction);
+            this.forwardRay.pointAt(globe.horizonDistance(camera.altitude), this.originPoint);
+            globe.cartesianToGeographic(this.originPoint.x, this.originPoint.y, this.originPoint.z, this.originPos);
+            globe.cartesianToLocalTransform(this.originPoint.x, this.originPoint.y, this.originPoint.z, this.origin);
         }
 
-        globe.cartesianToGeographic(this.originPoint.x, this.originPoint.y, this.originPoint.z, this.originPos);
-        globe.cartesianToLocalTransform(this.originPoint.x, this.originPoint.y, this.originPoint.z, this.origin);
         this.modelview.multiplyByMatrix(this.origin);
 
         result.latitude = this.originPos.latitude;
@@ -247,6 +264,25 @@ protected Camera lookAtToCamera(Globe globe, LookAt lookAt, Camera result) {
         result.tilt = this.modelview.extractTilt();
         result.roll = lookAt.roll; // roll passes straight through
 
+        // Check if camera altitude is not under the surface
+        double elevation = globe.getElevationAtLocation(result.latitude, result.longitude) * wwd.getVerticalExaggeration() + COLLISION_THRESHOLD;
+        if(elevation > result.altitude) {
+            // Set camera altitude above the surface
+            result.altitude = elevation;
+            // Compute new camera point
+            globe.geographicToCartesian(result.latitude, result.longitude, result.altitude, originPoint);
+            // Compute look at point
+            globe.geographicToCartesian(lookAt.latitude, lookAt.longitude, lookAt.altitude, forwardRay.origin);
+            // Compute normal to globe in look at point
+            globe.geographicToCartesianNormal(lookAt.latitude, lookAt.longitude, forwardRay.direction);
+            // Calculate tilt angle between new camera point and look at point
+            originPoint.subtract(forwardRay.origin).normalize();
+            double dot = forwardRay.direction.dot(originPoint);
+            if (dot >= -1 || dot <= 1) {
+                result.tilt = Math.toDegrees(Math.acos(dot));
+            }
+        }
+
         return result;
     }
 

worldwind/src/main/java/gov/nasa/worldwind/NavigatorEventSupport.java

@@ -41,6 +41,14 @@ public boolean handleMessage(Message msg) {
         }
     });
 
+    protected Handler moveHandler = new Handler(Looper.getMainLooper(), new Handler.Callback() {
+        @Override
+        public boolean handleMessage(Message msg) {
+            onNavigatorMoved();
+            return false;
+        }
+    });
+
     public NavigatorEventSupport(WorldWindow wwd) {
         if (wwd == null) {
             throw new IllegalArgumentException(
@@ -53,6 +61,7 @@ public NavigatorEventSupport(WorldWindow wwd) {
     public void reset() {
         this.lastModelview = null;
         this.stopHandler.removeMessages(0 /*what*/);
+        this.moveHandler.removeMessages(0 /*what*/);
 
         if (this.lastTouchEvent != null) {
             this.lastTouchEvent.recycle();
@@ -113,10 +122,14 @@ public void onFrameRendered(RenderContext rc) {
 
         if (this.lastModelview == null) { // this is the first frame; copy the frame's modelview
             this.lastModelview = new Matrix4(rc.modelview);
+            // Notify listeners with stopped event on first frame
+            this.stopHandler.removeMessages(0 /*what*/);
+            this.stopHandler.sendEmptyMessage(0 /*what*/);
         } else if (!this.lastModelview.equals(rc.modelview)) { // the frame's modelview has changed
             this.lastModelview.set(rc.modelview);
             // Notify the listeners of a navigator moved event.
-            this.onNavigatorMoved();
+            this.moveHandler.removeMessages(0 /*what*/);
+            this.moveHandler.sendEmptyMessage(0/*what*/);
             // Schedule a navigator stopped event after a specified delay in milliseconds.
             this.stopHandler.removeMessages(0 /*what*/);
             this.stopHandler.sendEmptyMessageDelayed(0 /*what*/, this.stoppedEventDelay);

worldwind/src/main/java/gov/nasa/worldwind/WorldWindow.java

@@ -75,7 +75,7 @@ public class WorldWindow extends GLSurfaceView implements Choreographer.FrameCal
 
     protected double fieldOfView = 45;
 
-    protected Navigator navigator = new Navigator();
+    protected Navigator navigator = new Navigator(this);
 
     protected NavigatorEventSupport navigatorEvents = new NavigatorEventSupport(this);
 
@@ -389,6 +389,10 @@ public void setRenderResourceCache(RenderResourceCache cache) {
         this.renderResourceCache = cache;
     }
 
+    public Viewport getViewport() {
+        return this.viewport;
+    }
+
     /**
      * Determines the WorldWind objects displayed at a screen point. The screen point is interpreted as coordinates in
      * Android screen pixels relative to this View.
@@ -1039,21 +1043,26 @@ protected void computeViewingTransform(Matrix4 projection, Matrix4 modelview) {
         double eyeAltitude = this.navigator.getAltitude();
         double eyeHorizon = this.globe.horizonDistance(eyeAltitude);
         double atmosphereHorizon = this.globe.horizonDistance(160000);
-        double near = eyeAltitude * 0.5;
-        double far = eyeHorizon + atmosphereHorizon;
 
-        // Computes the near clip distance that provides a minimum resolution at the far clip plane, based on the OpenGL
-        // context's depth buffer precision.
-        if (this.depthBits != 0) {
-            double maxDepthValue = (1 << this.depthBits) - 1;
-            double farResolution = 10.0;
-            double nearDistance = far / (maxDepthValue / (1 - farResolution / far) - maxDepthValue + 1);
-            // Use the computed near distance only when it's less than our default distance.
-            if (near > nearDistance) {
-                near = nearDistance;
-            }
+        // The far distance is set to the smallest value that does not clip the atmosphere.
+        double far = eyeHorizon + atmosphereHorizon;
+        if (far < 1e3) far = 1e3;
+
+        //The near distance is set to a large value that does not clip the globe's surface.
+        double maxDepthValue = (1L << this.depthBits) - 1L;
+        double farResolution = 10.0;
+        double near = far / (maxDepthValue / (1 - farResolution / far) - maxDepthValue + 1);
+
+        // Prevent the near clip plane from intersecting the terrain.
+        double distanceToSurface = this.navigator.getAltitude() - this.globe.getElevationAtLocation(this.navigator.getLatitude(), this.navigator.getLongitude()) * this.getVerticalExaggeration();
+        if (distanceToSurface > 0) {
+            double tanHalfFov = Math.tan(0.5 * Math.toRadians(this.fieldOfView));
+            double maxNearDistance = distanceToSurface / (2 * Math.sqrt(2 * tanHalfFov * tanHalfFov + 1));
+            if (near > maxNearDistance) near = maxNearDistance;
         }
 
+        if (near < 1) near = 1;
+
         // Compute a perspective projection matrix given the WorldWindow's viewport, field of view, and clip distances.
         projection.setToPerspectiveProjection(this.viewport.width, this.viewport.height, this.fieldOfView, near, far);
 

worldwind/src/main/java/gov/nasa/worldwind/globe/Globe.java

@@ -32,6 +32,10 @@ public class Globe {
      */
     protected GeographicProjection projection;
 
+    private final float[] scratchHeights = new float[1];
+
+    private final Sector scratchSector = new Sector();
+
     /**
      * Constructs a globe with a specified reference ellipsoid and projection.
      *
@@ -320,4 +324,19 @@ public boolean intersect(Line line, Vec3 result) {
 
         return this.projection.intersect(this, line, result);
     }
+
+    /**
+     * Determine terrain altitude in specified geographic point from elevation model
+     *
+     * @param latitude  location latitude
+     * @param longitude location longitude
+     *
+     * @return Elevation in meters in specified location
+     */
+    public double getElevationAtLocation(double latitude, double longitude) {
+        // Use 1E-15 below because sector can not have zero deltas
+        this.scratchSector.set(latitude, longitude, 1E-15, 1E-15);
+        this.getElevationModel().getHeightGrid(this.scratchSector, 1, 1, this.scratchHeights);
+        return this.scratchHeights[0];
+    }
 }