Math.cpp

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/*
 * Math.cpp
 *
 * Part of Fly! Legacy project
 *
 * Copyright 2003 Chris Wallace
 *
 * Fly! Legacy is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License as published by
 *   the Free Software Foundation; either version 2 of the License, or
 *   (at your option) any later version.
 *
 * Fly! Legacy is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *   GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 *   along with Fly! Legacy; if not, write to the Free Software
 *    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

#include "../Include/Utility.h"

//
// Wrap a float value to the range [0, 2 * PI), typically used to normalize
//   an angle in radians
//
double WrapTwoPi (double rad) {
  while (rad < 0)
    rad += (SG_PI * 2);
  while (rad > (SG_PI * 2))
    rad -= (SG_PI * 2);

  return rad;
}


//
// Wrap a float value to the range [0, PI), typically used to normalize
//   an angle in radians
//
double WrapPi (double rad) {
  while (rad < 0)
    rad += SG_PI;
  while (rad > SG_PI)
    rad -= SG_PI;

  return rad;
}


//
// Wrap a float value to the range [0, 360), typically used to normalize
//   an angle in degrees
//
double Wrap360 (double deg)
{
  while (deg < 0)
    deg += 360;
  while (deg >= 360)
    deg -= 360;

  return deg;
}

//
// Wrap an integer value to the range [0, 360), typically used to normalize
//   an angle in degrees
//
int Wrap360 (int deg)
{
  while (deg < 0)
    deg += 360;
  while (deg >= 360)
    deg -= 360;

  return deg;
}

//
// Wrap a float value to the range [-180, 180), typically used to normalize
//   an angle in degrees
//
double Wrap180 (double deg)
{
  // First wrap 0..360
  deg = Wrap360 (deg);

  if (deg > 180) {
    // Negate
    deg -= 360;
  }

  return deg;
}

//
// Wrap a float value to the range [0, 24), typically used to normalize
//   a value representing hours of the day
//
float Wrap24 (float hrs)
{
  while (hrs < 0.0f)
    hrs += 24.0f;
  while (hrs >= 24.0f)
    hrs -= 24.0f;

  return hrs;
}

//
// Wrap a float value to the range [0, 60), typically used to normalize
//   a value representing minutes in an hour or seconds in a minute
//
float Wrap60 (float min)
{
  while (min < 0.0f)
    min += 60.0f;
  while (min >= 60.0f)
    min -= 60.0f;

  return min;
}



Tag StringToTag (const char* s)
{
  Tag tag = 0;
  
  tag = (s[0] << 24)
    + (s[1] << 16)
    + (s[2] << 8)
    + (s[3]);
  return tag;
}

char *TagString (char* s, Tag tag)
{
  TagToString (s, tag);
  return s;
}

void TagToString (char* s, Tag tag)
{
  s[0] = (char)((tag >> 24) & 0xff);
  s[1] = (char)((tag >> 16) & 0xff);
  s[2] = (char)((tag >> 8) & 0xff);
  s[3] = (char)((tag) & 0xff);
  s[4] = '\0';
}


double WrapArcsec (double arcsec)
{
  double rc = arcsec;

  static const double WrapValue = (360 * 3600);

  while (rc < 0) rc += WrapValue;
  while (rc > WrapValue) rc -= WrapValue;

  return rc;
}


//
// Calculate the number of feet in one arcsecond of longitude at the given latitude.
//
// Arguments:
//    lat     Latitude in arcseconds (+ is N hemisphere)
//
double FeetPerLonArcsec (double lat)
{
  double latRad = DegToRad (lat / 3600.0);
  double circumference = cos(latRad) * MEAN_CIRCUMFERENCE;
  double feetPerLonArcsec = circumference / (360.0 * 3600.0);

  return feetPerLonArcsec;
}

//
// Calculate a new position based on a starting point and a vector offset in feet:
//   v.x = E/W offset      (+ is East)
//   v.y = N/S offset      (+ is North)
//   v.z = Altitude offset (+ is higher)
//
// This function is only accurate for small vector offsets (a few miles)
//
SPosition AddVector(SPosition &from, SVector &v)
{
  SPosition to;

  // Calculate arcseconds of latitude offset based on constants defined above
  double arcsecLat = v.y / FEET_PER_LAT_ARCSEC;
  to.lat = from.lat + arcsecLat;

  // Calculate actual number of feet per longitude arcsec at this latitude
  double feetPerLonArcsec = FeetPerLonArcsec (from.lat);
  double arcsecLon = v.x / feetPerLonArcsec;
  to.lon = WrapArcsec (from.lon + arcsecLon);

  // Altitude is already in feet, simply add the offset
  to.alt = from.alt + v.z;

  return to;
}

//
// SubtractVector computes a new global position based on a starting position
//   and an offset vector.  This is essentially the same as AddVector except
//   the distances are inverted (i.e. an argument to AddVector of +20 feet
//   is equivalent to the same argument to SubtractVector of -20 feet).
//
SPosition SubtractVector(SPosition &from, SVector &v)
{
  SVector vNew;
  vNew.x = -v.x;
  vNew.y = -v.y;
  vNew.z = -v.z;
  return AddVector (from, vNew);
}

//
// SubtractPosition computes the vector offset between two globe positions.
//   See "AddVector" for details on the result.
//
SVector SubtractPosition(SPosition &from, SPosition &to)
{
  SVector v;

  // Calculate number of arcseconds difference in latitude
  double arcsecLat = to.lat - from.lat;
  v.z = arcsecLat * FEET_PER_LAT_ARCSEC;

  // Calculate arcsecond difference in longitude
  double arcsecLon = WrapArcsec(to.lon - from.lon);
  v.x = arcsecLon * FeetPerLonArcsec (from.lat);

  // Altitude is already in feet, simply subtract
  v.y = to.alt - from.alt;

  return v;
}


//
// Unit conversion functions
//

float NmToMi (float nm)
{
  return (nm / MILES_PER_NM);
}

float MiToNm (float mi)
{
  return (mi * MILES_PER_NM);
}

float FeetToNm (float feet)
{
  return feet / FEET_PER_NM;
}

float NmToFeet (float nm)
{
  return nm * FEET_PER_NM;
}

float FpsToKt (float fps)
{
  return FeetToNm (fps * 3600);
}


// Metric conversions

double FeetToMetres (double ft)
{
  return (ft * METRES_PER_FOOT);
}

double MetresToFeet (double m)
{
  return (m / METRES_PER_FOOT);
}

float KmToNm (float km)
{
  return (km * KM_PER_NM);
}

float NmToKm (float nm)
{
  return (nm / KM_PER_NM);
}



// Trigonometric conversions

float RadToDeg (float rad)
{
  return rad * 180 / PI;
}

double RadToDeg (double rad)
{
  return rad * 180 / PI;
}

float DegToRad (float deg)
{
  return deg * PI / 180;
}

double DegToRad (double deg)
{
  return deg * PI / 180;
}


//
// Simple vector sum
//
SVector VectorSum (SVector v1, SVector v2)
{
  SVector rc;
  rc.x = v1.x + v2.x;
  rc.y = v1.y + v2.y;
  rc.z = v1.z + v2.z;
  return rc;
}


//
// Simple vector subtraction
//
SVector VectorDifference (SVector v1, SVector v2)
{
  SVector rc;
  rc.x = v1.x - v2.x;
  rc.y = v1.y - v2.y;
  rc.z = v1.z - v2.z;
  return rc;
}

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