Merge "Update GeomagneticField coefficients to WMM-2020"

package android.hardware;

import java.util.GregorianCalendar;

import java.util.Calendar;

import java.util.TimeZone;

/**

 * Estimates magnetic field at a given point on

    // These coefficients and the formulae used below are from:

    // NOAA Technical Report: The US/UK World Magnetic Model for 2020-2025

    static private final float[][] G_COEFF = new float[][]{

            {0.0f},

            {-29404.5f, -1450.7f},

            {3.0f, -1.4f, -2.5f, 2.4f, -0.9f, 0.3f, -0.7f, -0.1f, 1.4f, -0.6f, 0.2f, 3.1f},

            {-2.0f, -0.1f, 0.5f, 1.3f, -1.2f, 0.7f, 0.3f, 0.5f, -0.2f, -0.5f, 0.1f, -1.1f, -0.3f}};

    static private final float[][] H_COEFF = new float[][]{

            {0.0f},

            {0.0f, 4652.9f},

            {0.0f, 0.0f, 2.6f, -0.5f, -0.4f, 0.6f, -0.2f, -1.7f, -1.6f, -3.0f, -2.0f, -2.6f},

            {0.0f, -1.2f, 0.5f, 1.3f, -1.8f, 0.1f, 0.7f, -0.1f, 0.6f, 0.2f, -0.9f, 0.0f, 0.5f}};

    static private final float[][] DELTA_G = new float[][]{

            {0.0f},

            {6.7f, 7.7f},

            {0.0f, -0.1f, 0.0f, 0.0f, 0.0f, -0.1f, 0.0f, 0.0f, -0.1f, -0.1f, -0.1f, -0.1f},

            {0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, -0.1f}};

    static private final float[][] DELTA_H = new float[][]{

            {0.0f},

            {0.0f, -25.1f},

            {0.0f, 0.0f, 0.1f, 0.0f, 0.2f, 0.0f, 0.0f, 0.1f, 0.0f, -0.1f, 0.0f, 0.0f},

            {0.0f, 0.0f, 0.0f, -0.1f, 0.1f, 0.0f, 0.0f, 0.0f, 0.1f, 0.0f, 0.0f, 0.0f, -0.1f}};

    static private final long BASE_TIME =

            new GregorianCalendar(2020, 1, 1).getTimeInMillis();

    static private final long BASE_TIME = new Calendar.Builder()

            .setTimeZone(TimeZone.getTimeZone("UTC"))

            .setDate(2020, Calendar.JANUARY, 1)

            .build()

            .getTimeInMillis();

    // The ratio between the Gauss-normalized associated Legendre functions and

    // the Schmid quasi-normalized ones. Compute these once staticly since they

        // 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 2015-2020 for the derivation.

        // World Magnetic Model for 2020-2025 for the derivation.

        float gcX = 0.0f;  // Geocentric northwards component.

        float gcY = 0.0f;  // Geocentric eastwards component.

        float gcZ = 0.0f;  // Geocentric downwards component.

                // 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

                // NOAA Technical 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]