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author | The Android Open Source Project <initial-contribution@android.com> | 2009-03-03 18:28:45 -0800 |
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committer | The Android Open Source Project <initial-contribution@android.com> | 2009-03-03 18:28:45 -0800 |
commit | d83a98f4ce9cfa908f5c54bbd70f03eec07e7553 (patch) | |
tree | 4b825dc642cb6eb9a060e54bf8d69288fbee4904 /core/java/android/hardware/GeomagneticField.java | |
parent | 076357b8567458d4b6dfdcf839ef751634cd2bfb (diff) | |
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auto import from //depot/cupcake/@135843
Diffstat (limited to 'core/java/android/hardware/GeomagneticField.java')
-rw-r--r-- | core/java/android/hardware/GeomagneticField.java | 409 |
1 files changed, 0 insertions, 409 deletions
diff --git a/core/java/android/hardware/GeomagneticField.java b/core/java/android/hardware/GeomagneticField.java deleted file mode 100644 index b4c04b1..0000000 --- a/core/java/android/hardware/GeomagneticField.java +++ /dev/null @@ -1,409 +0,0 @@ -/* - * 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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