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diff --git a/core/java/android/hardware/GeomagneticField.java b/core/java/android/hardware/GeomagneticField.java
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+++ b/core/java/android/hardware/GeomagneticField.java
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+/*
+ * Copyright (C) 2009 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package android.hardware;
+
+import java.util.GregorianCalendar;
+
+/**
+ * This class is used to estimated estimate magnetic field at a given point on
+ * Earth, and in particular, to compute the magnetic declination from true
+ * north.
+ *
+ * <p>This uses the World Magnetic Model produced by the United States National
+ * Geospatial-Intelligence Agency.  More details about the model can be found at
+ * <a href="http://www.ngdc.noaa.gov/geomag/WMM/DoDWMM.shtml">http://www.ngdc.noaa.gov/geomag/WMM/DoDWMM.shtml</a>.
+ * This class currently uses WMM-2005 which is valid until 2010, but should
+ * produce acceptable results for several years after that.
+ */
+public class GeomagneticField {
+    // The magnetic field at a given point, in nonoteslas in geodetic
+    // coordinates.
+    private float mX;
+    private float mY;
+    private float mZ;
+
+    // Geocentric coordinates -- set by computeGeocentricCoordinates.
+    private float mGcLatitudeRad;
+    private float mGcLongitudeRad;
+    private float mGcRadiusKm;
+
+    // Constants from WGS84 (the coordinate system used by GPS)
+    static private final float EARTH_SEMI_MAJOR_AXIS_KM = 6378.137f;
+    static private final float EARTH_SEMI_MINOR_AXIS_KM = 6356.7523f;
+    static private final float EARTH_REFERENCE_RADIUS_KM = 6371.2f;
+
+    // These coefficients and the formulae used below are from:
+    // NOAA Technical Report: The US/UK World Magnetic Model for 2005-2010
+    static private final float[][] G_COEFF = new float[][] {
+        { 0f },
+        { -29556.8f, -1671.7f },
+        { -2340.6f, 3046.9f, 1657.0f },
+        { 1335.4f, -2305.1f, 1246.7f, 674.0f },
+        { 919.8f, 798.1f, 211.3f, -379.4f, 100.0f },
+        { -227.4f, 354.6f, 208.7f, -136.5f, -168.3f, -14.1f },
+        { 73.2f, 69.7f, 76.7f, -151.2f, -14.9f, 14.6f, -86.3f },
+        { 80.1f, -74.5f, -1.4f, 38.5f, 12.4f, 9.5f, 5.7f, 1.8f },
+        { 24.9f, 7.7f, -11.6f, -6.9f, -18.2f, 10.0f, 9.2f, -11.6f, -5.2f },
+        { 5.6f, 9.9f, 3.5f, -7.0f, 5.1f, -10.8f, -1.3f, 8.8f, -6.7f, -9.1f },
+        { -2.3f, -6.3f, 1.6f, -2.6f, 0.0f, 3.1f, 0.4f, 2.1f, 3.9f, -0.1f, -2.3f },
+        { 2.8f, -1.6f, -1.7f, 1.7f, -0.1f, 0.1f, -0.7f, 0.7f, 1.8f, 0.0f, 1.1f, 4.1f },
+        { -2.4f, -0.4f, 0.2f, 0.8f, -0.3f, 1.1f, -0.5f, 0.4f, -0.3f, -0.3f, -0.1f,
+          -0.3f, -0.1f } };
+
+    static private final float[][] H_COEFF = new float[][] {
+        { 0f },
+        { 0.0f, 5079.8f },
+        { 0.0f, -2594.7f, -516.7f },
+        { 0.0f, -199.9f, 269.3f, -524.2f },
+        { 0.0f, 281.5f, -226.0f, 145.8f, -304.7f },
+        { 0.0f, 42.4f, 179.8f, -123.0f, -19.5f, 103.6f },
+        { 0.0f, -20.3f, 54.7f, 63.6f, -63.4f, -0.1f, 50.4f },
+        { 0.0f, -61.5f, -22.4f, 7.2f, 25.4f, 11.0f, -26.4f, -5.1f },
+        { 0.0f, 11.2f, -21.0f, 9.6f, -19.8f, 16.1f, 7.7f, -12.9f, -0.2f },
+        { 0.0f, -20.1f, 12.9f, 12.6f, -6.7f, -8.1f, 8.0f, 2.9f, -7.9f, 6.0f },
+        { 0.0f, 2.4f, 0.2f, 4.4f, 4.8f, -6.5f, -1.1f, -3.4f, -0.8f, -2.3f, -7.9f },
+        { 0.0f, 0.3f, 1.2f, -0.8f, -2.5f, 0.9f, -0.6f, -2.7f, -0.9f, -1.3f, -2.0f, -1.2f },
+        { 0.0f, -0.4f, 0.3f, 2.4f, -2.6f, 0.6f, 0.3f, 0.0f, 0.0f, 0.3f, -0.9f, -0.4f,
+          0.8f } };
+
+    static private final float[][] DELTA_G = new float[][] {
+        { 0f },
+        { 8.0f, 10.6f },
+        { -15.1f, -7.8f, -0.8f },
+        { 0.4f, -2.6f, -1.2f, -6.5f },
+        { -2.5f, 2.8f, -7.0f, 6.2f, -3.8f },
+        { -2.8f, 0.7f, -3.2f, -1.1f, 0.1f, -0.8f },
+        { -0.7f, 0.4f, -0.3f, 2.3f, -2.1f, -0.6f, 1.4f },
+        { 0.2f, -0.1f, -0.3f, 1.1f, 0.6f, 0.5f, -0.4f, 0.6f },
+        { 0.1f, 0.3f, -0.4f, 0.3f, -0.3f, 0.2f, 0.4f, -0.7f, 0.4f },
+        { 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f },
+        { 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f },
+        { 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f },
+        { 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f } };
+
+    static private final float[][] DELTA_H = new float[][] {
+        { 0f },
+        { 0.0f, -20.9f },
+        { 0.0f, -23.2f, -14.6f },
+        { 0.0f, 5.0f, -7.0f, -0.6f },
+        { 0.0f, 2.2f, 1.6f, 5.8f, 0.1f },
+        { 0.0f, 0.0f, 1.7f, 2.1f, 4.8f, -1.1f },
+        { 0.0f, -0.6f, -1.9f, -0.4f, -0.5f, -0.3f, 0.7f },
+        { 0.0f, 0.6f, 0.4f, 0.2f, 0.3f, -0.8f, -0.2f, 0.1f },
+        { 0.0f, -0.2f, 0.1f, 0.3f, 0.4f, 0.1f, -0.2f, 0.4f, 0.4f },
+        { 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f },
+        { 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f },
+        { 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f },
+        { 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f } };
+
+    static private final long BASE_TIME =
+        new GregorianCalendar(2005, 1, 1).getTimeInMillis();
+
+    // The ratio between the Gauss-normalized associated Legendre functions and
+    // the Schmid quasi-normalized ones. Compute these once staticly since they
+    // don't depend on input variables at all.
+    static private final float[][] SCHMIDT_QUASI_NORM_FACTORS =
+        computeSchmidtQuasiNormFactors(G_COEFF.length);
+
+    /**
+     * Estimate the magnetic field at a given point and time.
+     *
+     * @param gdLatitudeDeg
+     *            Latitude in WGS84 geodetic coordinates -- positive is east.
+     * @param gdLongitudeDeg
+     *            Longitude in WGS84 geodetic coordinates -- positive is north.
+     * @param altitudeMeters
+     *            Altitude in WGS84 geodetic coordinates, in meters.
+     * @param timeMillis
+     *            Time at which to evaluate the declination, in milliseconds
+     *            since January 1, 1970. (approximate is fine -- the declination
+     *            changes very slowly).
+     */
+    public GeomagneticField(float gdLatitudeDeg,
+                            float gdLongitudeDeg,
+                            float altitudeMeters,
+                            long timeMillis) {
+        final int MAX_N = G_COEFF.length; // Maximum degree of the coefficients.
+
+        // We don't handle the north and south poles correctly -- pretend that
+        // we're not quite at them to avoid crashing.
+        gdLatitudeDeg = Math.min(90.0f - 1e-5f,
+                                 Math.max(-90.0f + 1e-5f, gdLatitudeDeg));
+        computeGeocentricCoordinates(gdLatitudeDeg,
+                                     gdLongitudeDeg,
+                                     altitudeMeters);
+
+        assert G_COEFF.length == H_COEFF.length;
+
+        // Note: LegendreTable computes associated Legendre functions for
+        // cos(theta).  We want the associated Legendre functions for
+        // sin(latitude), which is the same as cos(PI/2 - latitude), except the
+        // derivate will be negated.
+        LegendreTable legendre =
+            new LegendreTable(MAX_N - 1,
+                              (float) (Math.PI / 2.0 - mGcLatitudeRad));
+
+        // Compute a table of (EARTH_REFERENCE_RADIUS_KM / radius)^n for i in
+        // 0..MAX_N-2 (this is much faster than calling Math.pow MAX_N+1 times).
+        float[] relativeRadiusPower = new float[MAX_N + 2];
+        relativeRadiusPower[0] = 1.0f;
+        relativeRadiusPower[1] = EARTH_REFERENCE_RADIUS_KM / mGcRadiusKm;
+        for (int i = 2; i < relativeRadiusPower.length; ++i) {
+            relativeRadiusPower[i] = relativeRadiusPower[i - 1] *
+                relativeRadiusPower[1];
+        }
+
+        // Compute tables of sin(lon * m) and cos(lon * m) for m = 0..MAX_N --
+        // this is much faster than calling Math.sin and Math.com MAX_N+1 times.
+        float[] sinMLon = new float[MAX_N];
+        float[] cosMLon = new float[MAX_N];
+        sinMLon[0] = 0.0f;
+        cosMLon[0] = 1.0f;
+        sinMLon[1] = (float) Math.sin(mGcLongitudeRad);
+        cosMLon[1] = (float) Math.cos(mGcLongitudeRad);
+
+        for (int m = 2; m < MAX_N; ++m) {
+            // Standard expansions for sin((m-x)*theta + x*theta) and
+            // cos((m-x)*theta + x*theta).
+            int x = m >> 1;
+            sinMLon[m] = sinMLon[m-x] * cosMLon[x] + cosMLon[m-x] * sinMLon[x];
+            cosMLon[m] = cosMLon[m-x] * cosMLon[x] - sinMLon[m-x] * sinMLon[x];
+        }
+
+        float inverseCosLatitude = 1.0f / (float) Math.cos(mGcLatitudeRad);
+        float yearsSinceBase =
+            (timeMillis - BASE_TIME) / (365f * 24f * 60f * 60f * 1000f);
+
+        // We now compute the magnetic field strength given the geocentric
+        // location. The magnetic field is the derivative of the potential
+        // function defined by the model. See NOAA Technical Report: The US/UK
+        // World Magnetic Model for 2005-2010 for the derivation.
+        float gcX = 0.0f;  // Geocentric northwards component.
+        float gcY = 0.0f;  // Geocentric eastwards component.
+        float gcZ = 0.0f;  // Geocentric downwards component.
+
+        for (int n = 1; n < MAX_N; n++) {
+            for (int m = 0; m <= n; m++) {
+                // Adjust the coefficients for the current date.
+                float g = G_COEFF[n][m] + yearsSinceBase * DELTA_G[n][m];
+                float h = H_COEFF[n][m] + yearsSinceBase * DELTA_H[n][m];
+
+                // Negative derivative with respect to latitude, divided by
+                // radius.  This looks like the negation of the version in the
+                // NOAA Techincal report because that report used
+                // P_n^m(sin(theta)) and we use P_n^m(cos(90 - theta)), so the
+                // derivative with respect to theta is negated.
+                gcX += relativeRadiusPower[n+2]
+                    * (g * cosMLon[m] + h * sinMLon[m])
+                    * legendre.mPDeriv[n][m]
+                    * SCHMIDT_QUASI_NORM_FACTORS[n][m];
+
+                // Negative derivative with respect to longitude, divided by
+                // radius.
+                gcY += relativeRadiusPower[n+2] * m
+                    * (g * sinMLon[m] - h * cosMLon[m])
+                    * legendre.mP[n][m]
+                    * SCHMIDT_QUASI_NORM_FACTORS[n][m]
+                    * inverseCosLatitude;
+
+                // Negative derivative with respect to radius.
+                gcZ -= (n + 1) * relativeRadiusPower[n+2]
+                    * (g * cosMLon[m] + h * sinMLon[m])
+                    * legendre.mP[n][m]
+                    * SCHMIDT_QUASI_NORM_FACTORS[n][m];
+            }
+        }
+
+        // Convert back to geodetic coordinates.  This is basically just a
+        // rotation around the Y-axis by the difference in latitudes between the
+        // geocentric frame and the geodetic frame.
+        double latDiffRad = Math.toRadians(gdLatitudeDeg) - mGcLatitudeRad;
+        mX = (float) (gcX * Math.cos(latDiffRad)
+                      + gcZ * Math.sin(latDiffRad));
+        mY = gcY;
+        mZ = (float) (- gcX * Math.sin(latDiffRad)
+                      + gcZ * Math.cos(latDiffRad));
+    }
+
+    /**
+     * @return The X (northward) component of the magnetic field in nanoteslas.
+     */
+    public float getX() {
+        return mX;
+    }
+
+    /**
+     * @return The Y (eastward) component of the magnetic field in nanoteslas.
+     */
+    public float getY() {
+        return mY;
+    }
+
+    /**
+     * @return The Z (downward) component of the magnetic field in nanoteslas.
+     */
+    public float getZ() {
+        return mZ;
+    }
+
+    /**
+     * @return The declination of the horizontal component of the magnetic
+     *         field from true north, in degrees (i.e. positive means the
+     *         magnetic field is rotated east that much from true north).
+     */
+    public float getDeclination() {
+        return (float) Math.toDegrees(Math.atan2(mY, mX));
+    }
+
+    /**
+     * @return The inclination of the magnetic field in degrees -- positive
+     *         means the magnetic field is rotated downwards.
+     */
+    public float getInclination() {
+        return (float) Math.toDegrees(Math.atan2(mZ,
+                                                 getHorizontalStrength()));
+    }
+
+    /**
+     * @return  Horizontal component of the field strength in nonoteslas.
+     */
+    public float getHorizontalStrength() {
+        return (float) Math.sqrt(mX * mX + mY * mY);
+    }
+
+    /**
+     * @return  Total field strength in nanoteslas.
+     */
+    public float getFieldStrength() {
+        return (float) Math.sqrt(mX * mX + mY * mY + mZ * mZ);
+    }
+
+    /**
+     * @param gdLatitudeDeg
+     *            Latitude in WGS84 geodetic coordinates.
+     * @param gdLongitudeDeg
+     *            Longitude in WGS84 geodetic coordinates.
+     * @param altitudeMeters
+     *            Altitude above sea level in WGS84 geodetic coordinates.
+     * @return Geocentric latitude (i.e. angle between closest point on the
+     *         equator and this point, at the center of the earth.
+     */
+    private void computeGeocentricCoordinates(float gdLatitudeDeg,
+                                              float gdLongitudeDeg,
+                                              float altitudeMeters) {
+        float altitudeKm = altitudeMeters / 1000.0f;
+        float a2 = EARTH_SEMI_MAJOR_AXIS_KM * EARTH_SEMI_MAJOR_AXIS_KM;
+        float b2 = EARTH_SEMI_MINOR_AXIS_KM * EARTH_SEMI_MINOR_AXIS_KM;
+        double gdLatRad = Math.toRadians(gdLatitudeDeg);
+        float clat = (float) Math.cos(gdLatRad);
+        float slat = (float) Math.sin(gdLatRad);
+        float tlat = slat / clat;
+        float latRad =
+            (float) Math.sqrt(a2 * clat * clat + b2 * slat * slat);
+
+        mGcLatitudeRad = (float) Math.atan(tlat * (latRad * altitudeKm + b2)
+                                           / (latRad * altitudeKm + a2));
+
+        mGcLongitudeRad = (float) Math.toRadians(gdLongitudeDeg);
+
+        float radSq = altitudeKm * altitudeKm
+            + 2 * altitudeKm * (float) Math.sqrt(a2 * clat * clat +
+                                                 b2 * slat * slat)
+            + (a2 * a2 * clat * clat + b2 * b2 * slat * slat)
+            / (a2 * clat * clat + b2 * slat * slat);
+        mGcRadiusKm = (float) Math.sqrt(radSq);
+    }
+
+
+    /**
+     * Utility class to compute a table of Gauss-normalized associated Legendre
+     * functions P_n^m(cos(theta))
+     */
+    static private class LegendreTable {
+        // These are the Gauss-normalized associated Legendre functions -- that
+        // is, they are normal Legendre functions multiplied by
+        // (n-m)!/(2n-1)!! (where (2n-1)!! = 1*3*5*...*2n-1)
+        public final float[][] mP;
+
+        // Derivative of mP, with respect to theta.
+        public final float[][] mPDeriv;
+
+        /**
+         * @param maxN
+         *            The maximum n- and m-values to support
+         * @param thetaRad
+         *            Returned functions will be Gauss-normalized
+         *            P_n^m(cos(thetaRad)), with thetaRad in radians.
+         */
+        public LegendreTable(int maxN, float thetaRad) {
+            // Compute the table of Gauss-normalized associated Legendre
+            // functions using standard recursion relations. Also compute the
+            // table of derivatives using the derivative of the recursion
+            // relations.
+            float cos = (float) Math.cos(thetaRad);
+            float sin = (float) Math.sin(thetaRad);
+
+            mP = new float[maxN + 1][];
+            mPDeriv = new float[maxN + 1][];
+            mP[0] = new float[] { 1.0f };
+            mPDeriv[0] = new float[] { 0.0f };
+            for (int n = 1; n <= maxN; n++) {
+            	mP[n] = new float[n + 1];
+                mPDeriv[n] = new float[n + 1];
+                for (int m = 0; m <= n; m++) {
+                    if (n == m) {
+                        mP[n][m] = sin * mP[n - 1][m - 1];
+                        mPDeriv[n][m] = cos * mP[n - 1][m - 1]
+                            + sin * mPDeriv[n - 1][m - 1];
+                    } else if (n == 1 || m == n - 1) {
+                        mP[n][m] = cos * mP[n - 1][m];
+                        mPDeriv[n][m] = -sin * mP[n - 1][m]
+                            + cos * mPDeriv[n - 1][m];
+                    } else {
+                        assert n > 1 && m < n - 1;
+                        float k = ((n - 1) * (n - 1) - m * m)
+                            / (float) ((2 * n - 1) * (2 * n - 3));
+                        mP[n][m] = cos * mP[n - 1][m] - k * mP[n - 2][m];
+                        mPDeriv[n][m] = -sin * mP[n - 1][m]
+                            + cos * mPDeriv[n - 1][m] - k * mPDeriv[n - 2][m];
+                    }
+                }
+            }
+        }
+    }
+
+    /**
+     * Compute the ration between the Gauss-normalized associated Legendre
+     * functions and the Schmidt quasi-normalized version. This is equivalent to
+     * sqrt((m==0?1:2)*(n-m)!/(n+m!))*(2n-1)!!/(n-m)!
+     */
+    private static float[][] computeSchmidtQuasiNormFactors(int maxN) {
+        float[][] schmidtQuasiNorm = new float[maxN + 1][];
+        schmidtQuasiNorm[0] = new float[] { 1.0f };
+        for (int n = 1; n <= maxN; n++) {
+            schmidtQuasiNorm[n] = new float[n + 1];
+            schmidtQuasiNorm[n][0] =
+                schmidtQuasiNorm[n - 1][0] * (2 * n - 1) / (float) n;
+            for (int m = 1; m <= n; m++) {
+                schmidtQuasiNorm[n][m] = schmidtQuasiNorm[n][m - 1]
+                    * (float) Math.sqrt((n - m + 1) * (m == 1 ? 2 : 1)
+                                / (float) (n + m));
+            }
+        }
+        return schmidtQuasiNorm;
+    }
+}
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