git.gag.com Git - debian/openrocket/blob - src/net/sf/openrocket/util/GeodeticComputationStrategy.java

   1 package net.sf.openrocket.util;
   2
   3 import net.sf.openrocket.l10n.Translator;
   4 import net.sf.openrocket.startup.Application;
   5
   6 /**
   7  * A strategy that performs computations on WorldCoordinates.
   8  * <p>
   9  * The directions of the coordinate is:
  10  *   positive X = EAST
  11  *   positive Y = NORTH
  12  *   positive Z = UPWARDS
  13  */
  14 public enum GeodeticComputationStrategy {
  15
  16
  17         /**
  18          * Perform computations using a flat Earth approximation.  addCoordinate computes the
  19          * location using a direct meters-per-degree scaling and getCoriolisAcceleration always
  20          * returns NUL.
  21          */
  22         FLAT {
  23                 private static final double METERS_PER_DEGREE_LATITUDE = 111325; // "standard figure"
  24                 private static final double METERS_PER_DEGREE_LONGITUDE_EQUATOR = 111050;
  25
  26
  27                 @Override
  28                 public WorldCoordinate addCoordinate(WorldCoordinate location, Coordinate delta) {
  29
  30                         double metersPerDegreeLongitude = METERS_PER_DEGREE_LONGITUDE_EQUATOR * Math.cos(location.getLatitudeRad());
  31                         // Limit to 1 meter per degree near poles
  32                         metersPerDegreeLongitude = MathUtil.max(metersPerDegreeLongitude, 1);
  33
  34                         double newLat = location.getLatitudeDeg() + delta.y / METERS_PER_DEGREE_LATITUDE;
  35                         double newLon = location.getLongitudeDeg() + delta.x / metersPerDegreeLongitude;
  36                         double newAlt = location.getAltitude() + delta.z;
  37
  38                         return new WorldCoordinate(newLat, newLon, newAlt);
  39                 }
  40
  41                 @Override
  42                 public Coordinate getCoriolisAcceleration(WorldCoordinate location, Coordinate velocity) {
  43                         return Coordinate.NUL;
  44                 }
  45         },
  46
  47         /**
  48          * Perform geodetic computations with a spherical Earch approximation.
  49          */
  50         SPHERICAL {
  51
  52                 @Override
  53                 public WorldCoordinate addCoordinate(WorldCoordinate location, Coordinate delta) {
  54                         double newAlt = location.getAltitude() + delta.z;
  55
  56                         // bearing (in radians, clockwise from north);
  57                         // d/R is the angular distance (in radians), where d is the distance traveled and R is the earth's radius
  58                         double d = MathUtil.hypot(delta.x, delta.y);
  59
  60                         // Check for zero movement before computing bearing
  61                         if (MathUtil.equals(d, 0)) {
  62                                 return new WorldCoordinate(location.getLatitudeDeg(), location.getLongitudeDeg(), newAlt);
  63                         }
  64
  65                         double bearing = Math.atan2(delta.x, delta.y);
  66
  67                         // Calculate the new lat and lon
  68                         double newLat, newLon;
  69                         double sinLat = Math.sin(location.getLatitudeRad());
  70                         double cosLat = Math.cos(location.getLatitudeRad());
  71                         double sinDR = Math.sin(d / WorldCoordinate.REARTH);
  72                         double cosDR = Math.cos(d / WorldCoordinate.REARTH);
  73
  74                         newLat = Math.asin(sinLat * cosDR + cosLat * sinDR * Math.cos(bearing));
  75                         newLon = location.getLongitudeRad() + Math.atan2(Math.sin(bearing) * sinDR * cosLat, cosDR - sinLat * Math.sin(newLat));
  76
  77                         if (Double.isNaN(newLat) || Double.isNaN(newLon)) {
  78                                 throw new BugException("addCoordinate resulted in NaN location:  location=" + location + " delta=" + delta
  79                                                 + " newLat=" + newLat + " newLon=" + newLon);
  80                         }
  81
  82                         return new WorldCoordinate(Math.toDegrees(newLat), Math.toDegrees(newLon), newAlt);
  83                 }
  84
  85                 @Override
  86                 public Coordinate getCoriolisAcceleration(WorldCoordinate location, Coordinate velocity) {
  87                         return computeCoriolisAcceleration(location, velocity);
  88                 }
  89
  90         },
  91
  92         /**
  93          * Perform geodetic computations on a WGS84 reference ellipsoid using Vincenty Direct Solution.
  94          */
  95         WGS84 {
  96
  97                 @Override
  98                 public WorldCoordinate addCoordinate(WorldCoordinate location, Coordinate delta) {
  99                         double newAlt = location.getAltitude() + delta.z;
 100
 101                         // bearing (in radians, clockwise from north);
 102                         // d/R is the angular distance (in radians), where d is the distance traveled and R is the earth's radius
 103                         double d = MathUtil.hypot(delta.x, delta.y);
 104
 105                         // Check for zero movement before computing bearing
 106                         if (MathUtil.equals(d, 0)) {
 107                                 return new WorldCoordinate(location.getLatitudeDeg(), location.getLongitudeDeg(), newAlt);
 108                         }
 109
 110                         double bearing = Math.atan(delta.x / delta.y);
 111                         if (delta.y < 0)
 112                                 bearing = bearing + Math.PI;
 113
 114                         // Calculate the new lat and lon
 115                         double newLat, newLon;
 116                         double ret[] = dirct1(location.getLatitudeRad(), location.getLongitudeRad(), bearing, d, 6378137, 1.0 / 298.25722210088);
 117                         newLat = ret[0];
 118                         newLon = ret[1];
 119
 120                         if (Double.isNaN(newLat) || Double.isNaN(newLon)) {
 121                                 throw new BugException("addCoordinate resulted in NaN location:  location=" + location + " delta=" + delta
 122                                                 + " newLat=" + newLat + " newLon=" + newLon);
 123                         }
 124
 125                         return new WorldCoordinate(Math.toDegrees(newLat), Math.toDegrees(newLon), newAlt);
 126                 }
 127
 128                 @Override
 129                 public Coordinate getCoriolisAcceleration(WorldCoordinate location, Coordinate velocity) {
 130                         return computeCoriolisAcceleration(location, velocity);
 131                 }
 132         };
 133
 134
 135         private static final Translator trans = Application.getTranslator();
 136
 137         private static final double PRECISION_LIMIT = 0.5e-13;
 138
 139
 140         /**
 141          * Return the name of this geodetic computation method.
 142          */
 143         public String getName() {
 144                 return trans.get(name().toLowerCase() + ".name");
 145         }
 146
 147         /**
 148          * Return a description of the geodetic computation methods.
 149          */
 150         public String getDescription() {
 151                 return trans.get(name().toLowerCase() + ".desc");
 152         }
 153
 154         @Override
 155         public String toString() {
 156                 return getName();
 157         }
 158
 159
 160         /**
 161          * Add a cartesian movement coordinate to a WorldCoordinate.
 162          */
 163         public abstract WorldCoordinate addCoordinate(WorldCoordinate location, Coordinate delta);
 164
 165
 166         /**
 167          * Compute the coriolis acceleration at a specified WorldCoordinate and velocity.
 168          */
 169         public abstract Coordinate getCoriolisAcceleration(WorldCoordinate location, Coordinate velocity);
 170
 171
 172
 173
 174
 175         private static Coordinate computeCoriolisAcceleration(WorldCoordinate latlon, Coordinate velocity) {
 176
 177                 double sinlat = Math.sin(latlon.getLatitudeRad());
 178                 double coslat = Math.cos(latlon.getLatitudeRad());
 179
 180                 double v_n = velocity.y;
 181                 double v_e = -1 * velocity.x;
 182                 double v_u = velocity.z;
 183
 184                 // Not exactly sure why I have to reverse the x direction, but this gives the precession in the
 185                 // correct direction (e.g, flying north in northern hemisphere should cause defection to the east (+ve x))
 186                 // All the directions are very confusing because they are tied to the wind direction (to/from?), in which
 187                 // +ve x or east according to WorldCoordinate is what everything is relative to.
 188                 // The directions of everything need so thought, ideally the wind direction and launch rod should be
 189                 // able to be set independently and in terms of bearing with north == +ve y.
 190
 191                 Coordinate coriolis = new Coordinate(2.0 * WorldCoordinate.EROT * (v_n * sinlat - v_u * coslat),
 192                                                                                                 2.0 * WorldCoordinate.EROT * (-1.0 * v_e * sinlat),
 193                                                                                                 2.0 * WorldCoordinate.EROT * (v_e * coslat)
 194                                                                                         );
 195                 return coriolis;
 196         }
 197
 198
 199
 200         // ******************************************************************** //
 201         // The Vincenty Direct Solution.
 202         // Code from GeoConstants.java, Ian Cameron Smith, GPL
 203         // ******************************************************************** //
 204
 205         /**
 206          * Solution of the geodetic direct problem after T. Vincenty.
 207          * Modified Rainsford's method with Helmert's elliptical terms.
 208          * Effective in any azimuth and at any distance short of antipodal.
 209          *
 210          * Programmed for the CDC-6600 by lcdr L. Pfeifer, NGS Rockville MD,
 211          * 20 Feb 1975.
 212          *
 213          * @param       glat1           The latitude of the starting point, in radians,
 214          *                                              positive north.
 215          * @param       glon1           The latitude of the starting point, in radians,
 216          *                                              positive east.
 217          * @param       azimuth         The azimuth to the desired location, in radians
 218          *                                              clockwise from north.
 219          * @param       dist            The distance to the desired location, in meters.
 220          * @param       axis            The semi-major axis of the reference ellipsoid,
 221          *                                              in meters.
 222          * @param       flat            The flattening of the reference ellipsoid.
 223          * @return                              An array containing the latitude and longitude
 224          *                                              of the desired point, in radians, and the
 225          *                                              azimuth back from that point to the starting
 226          *                                              point, in radians clockwise from north.
 227          */
 228         private static double[] dirct1(double glat1, double glon1,
 229                                                                         double azimuth, double dist,
 230                                                                         double axis, double flat) {
 231                 double r = 1.0 - flat;
 232
 233                 double tu = r * Math.sin(glat1) / Math.cos(glat1);
 234
 235                 double sf = Math.sin(azimuth);
 236                 double cf = Math.cos(azimuth);
 237
 238                 double baz = 0.0;
 239
 240                 if (cf != 0.0)
 241                         baz = Math.atan2(tu, cf) * 2.0;
 242
 243                 double cu = 1.0 / Math.sqrt(tu * tu + 1.0);
 244                 double su = tu * cu;
 245                 double sa = cu * sf;
 246                 double c2a = -sa * sa + 1.0;
 247
 248                 double x = Math.sqrt((1.0 / r / r - 1.0) * c2a + 1.0) + 1.0;
 249                 x = (x - 2.0) / x;
 250                 double c = 1.0 - x;
 251                 c = (x * x / 4.0 + 1) / c;
 252                 double d = (0.375 * x * x - 1.0) * x;
 253                 tu = dist / r / axis / c;
 254                 double y = tu;
 255
 256                 double sy, cy, cz, e;
 257                 do {
 258                         sy = Math.sin(y);
 259                         cy = Math.cos(y);
 260                         cz = Math.cos(baz + y);
 261                         e = cz * cz * 2.0 - 1.0;
 262
 263                         c = y;
 264                         x = e * cy;
 265                         y = e + e - 1.0;
 266                         y = (((sy * sy * 4.0 - 3.0) * y * cz * d / 6.0 + x) *
 267                                                                         d / 4.0 - cz) * sy * d + tu;
 268                 } while (Math.abs(y - c) > PRECISION_LIMIT);
 269
 270                 baz = cu * cy * cf - su * sy;
 271                 c = r * Math.sqrt(sa * sa + baz * baz);
 272                 d = su * cy + cu * sy * cf;
 273                 double glat2 = Math.atan2(d, c);
 274                 c = cu * cy - su * sy * cf;
 275                 x = Math.atan2(sy * sf, c);
 276                 c = ((-3.0 * c2a + 4.0) * flat + 4.0) * c2a * flat / 16.0;
 277                 d = ((e * cy * c + cz) * sy * c + y) * sa;
 278                 double glon2 = glon1 + x - (1.0 - c) * d * flat;
 279                 baz = Math.atan2(sa, baz) + Math.PI;
 280
 281                 double[] ret = new double[3];
 282                 ret[0] = glat2;
 283                 ret[1] = glon2;
 284                 ret[2] = baz;
 285                 return ret;
 286         }
 287
 288
 289 }