package geography;
/**
 *  An abstract class that is extended to construct different types
 *  map projections.
 *
 *  @author  Prof. David Bernstein, James Madison University
 *  @version 1.0
 */
public abstract class AbstractMapProjection implements MapProjection
{
  // Radius of spherical Earth (in km)
  protected static final double R = 6369.0;

  protected static final double PI      = Math.PI;
  protected static final double TWO_PI   = 2.0*Math.PI;
  protected static final double PI_OVER_TWO = Math.PI/2.0;
  protected static final double PI_OVER_FOUR = Math.PI/4.0;

  protected static final double RADIANS_PER_DEGREE = 2.0*Math.PI/360.0;

  protected static final double DEGREES_PER_RADIAN  = 1.0 / RADIANS_PER_DEGREE;



  /**
   * The forward transformation (i.e., from Longitude/Latitude in
   * __degrees__ to kilometers above the equator and to the west of the
   * reference meridian).
   *
   * @param ll The longitude and latitude in __degrees__ (in that order)
   * @return   KMs west of reference and north of equator (in that order)
   */
  @Override
  public double[] forward(final double[] ll)
  {
    double lambda = ll[0] * RADIANS_PER_DEGREE;
    double phi    = ll[1] * RADIANS_PER_DEGREE;

    return forward(lambda, phi);
  }



  /**
   * The forward transformation (i.e., from Longitude/Latitude in
   * __radians__ to kilometers above the equator and to the west of the
   * reference meridian).
   *
   * @param lambda The longitude in __radians__
   * @param phi    The latitude in __radians__
   * @return   KMs west of reference and north of equator (in that order)
   */
  @Override
  public abstract double[] forward(final double lambda, final double phi);


  /**
   * The inverse transformation from kilometers (above the 
   * equator and to the west of the reference meridian)
   * to Longitude/Latitude in __degrees__.
   *
   * @param km The point in above,west coordinates (in that order)
   * @return   The longitude and latitude in __degrees__ (in that order)
   */
  @Override
  public double[] inverse(final double[] km)
  {
    double[] ll = inverse(km[0], km[1]);// In radians
    ll[0] = ll[0] * DEGREES_PER_RADIAN; // In degrees
    ll[1] = ll[1] * DEGREES_PER_RADIAN; // In degrees

    return ll;
  }


  /**
   * The inverse transformation from kilometers (above the 
   * equator and to the west of the reference meridian)
   * to Longitude/Latitude in __radians__.
   *
   * @param ew The distance east/west in kilometers
   * @param ns The distance north/south in kilometers
   * @return   The longitude and latitude in __radians__ (in that order)
   */
  @Override
  public abstract double[] inverse(final double ew, final double ns);

}