src/Environment/ridge_lift.cxx

   1 // simulates ridge lift
   2 //
   3 // Written by Patrice Poly
   4 // Copyright (C) 2009 Patrice Poly - p.polypa@gmail.com
   5 //
   6 //
   7 // Entirely based  on the paper :
   8 // http://carrier.csi.cam.ac.uk/forsterlewis/soaring/sim/fsx/dev/sim_probe/sim_probe_paper.html
   9 // by Ian Forster-Lewis, University of Cambridge, 26th December 2007
  10 //
  11 //
  12 // This program is free software; you can redistribute it and/or
  13 // modify it under the terms of the GNU General Public License as
  14 // published by the Free Software Foundation; either version 2 of the
  15 // License, or (at your option) any later version.
  16 //
  17 // This program is distributed in the hope that it will be useful, but
  18 // WITHOUT ANY WARRANTY; without even the implied warranty of
  19 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  20 // General Public License for more details.
  21 //
  22 // You should have received a copy of the GNU General Public License
  23 // along with this program; if not, write to the Free Software
  24 // Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
  25 //
  26 //
  27
  28
  29 #ifdef HAVE_CONFIG_H
  30 #  include <config.h>
  31 #endif
  32
  33 #include <Main/fg_props.hxx>
  34 #include <Main/globals.hxx>
  35 #include <Main/util.hxx>
  36 #include <Scenery/scenery.hxx>
  37 #include <string>
  38 #include <math.h>
  39
  40
  41 using std::string;
  42
  43 #include "ridge_lift.hxx"
  44
  45 static string CreateIndexedPropertyName(string Property, int index)
  46 {
  47         std::stringstream str;
  48         str << index;
  49         string tmp;
  50         str >> tmp;
  51         return Property + "[" + tmp + "]";
  52 }
  53
  54 static inline double sign(double x) {
  55         return x == 0 ? 0 : x > 0 ? 1.0 : -1.0;
  56 }
  57
  58 static const double BOUNDARY1_m = 40.0;
  59
  60 const double FGRidgeLift::dist_probe_m[] = { // in meters
  61      0.0,
  62    250.0,
  63    750.0,
  64   2000.0,
  65   -100.0
  66 };
  67
  68 //constructor
  69 FGRidgeLift::FGRidgeLift ()
  70 {
  71         strength = 0.0;
  72         timer = 0.0;
  73         for( int i = 0; i < 5; i++ )
  74                 probe_elev_m[i] = probe_lat_deg[i] = probe_lon_deg[i] = 0.0;
  75
  76         for( int i = 0; i < 4; i++ )
  77                 slope[i] = 0.0;
  78 }
  79
  80 //destructor
  81 FGRidgeLift::~FGRidgeLift()
  82 {
  83
  84 }
  85
  86 void FGRidgeLift::init(void)
  87 {
  88         _enabled_node = fgGetNode( "/environment/ridge-lift/enabled", false );
  89
  90         _ridge_lift_fps_node = fgGetNode("/environment/ridge-lift-fps", true);
  91         _surface_wind_from_deg_node =
  92                         fgGetNode("/environment/config/boundary/entry[0]/wind-from-heading-deg"
  93                         , true);
  94         _surface_wind_speed_node =
  95                         fgGetNode("/environment/config/boundary/entry[0]/wind-speed-kt"
  96                         , true);
  97         _user_longitude_node = fgGetNode("/position/longitude-deg", true);
  98         _user_latitude_node = fgGetNode("/position/latitude-deg", true);
  99         _user_altitude_agl_ft_node = fgGetNode("/position/altitude-agl-ft", true);
 100         _ground_elev_node = fgGetNode("/position/ground-elev-ft", true );
 101 }
 102
 103 void FGRidgeLift::bind() {
 104         string prop;
 105
 106         for( int i = 0; i < 5; i++ ) {
 107                 prop = CreateIndexedPropertyName("/environment/ridge-lift/probe-elev-m", i );
 108                 fgTie( prop.c_str(), this, i, &FGRidgeLift::get_probe_elev_m); // read-only
 109
 110                 prop = CreateIndexedPropertyName("/environment/ridge-lift/probe-lat-deg", i );
 111                 fgTie( prop.c_str(), this, i, &FGRidgeLift::get_probe_lat_deg); // read-only
 112
 113                 prop = CreateIndexedPropertyName("/environment/ridge-lift/probe-lon-deg", i );
 114                 fgTie( prop.c_str(), this, i, &FGRidgeLift::get_probe_lon_deg); // read-only
 115         }
 116
 117         for( int i = 0; i < 4; i++ ) {
 118                 prop = CreateIndexedPropertyName("/environment/ridge-lift/slope", i );
 119                 fgTie( prop.c_str(), this, i, &FGRidgeLift::get_slope); // read-only
 120         }
 121 }
 122
 123 void FGRidgeLift::unbind() {
 124         string prop;
 125
 126         for( int i = 0; i < 5; i++ ) {
 127
 128                 prop = CreateIndexedPropertyName("/environment/ridge-lift/probe-elev-m", i );
 129                 fgUntie( prop.c_str() );
 130
 131                 prop = CreateIndexedPropertyName("/environment/ridge-lift/probe-lat-deg", i );
 132                 fgUntie( prop.c_str() );
 133
 134                 prop = CreateIndexedPropertyName("/environment/ridge-lift/probe-lon-deg", i );
 135                 fgUntie( prop.c_str() );
 136         }
 137
 138         for( int i = 0; i < 4; i++ ) {
 139                 prop = CreateIndexedPropertyName("/environment/ridge-lift/slope", i );
 140                 fgUntie( prop.c_str() );
 141         }
 142 }
 143
 144 void FGRidgeLift::update(double dt) {
 145
 146         if( dt <= SGLimitsd::min() ) // paused, do nothing but keep current lift
 147                 return;
 148
 149         if( _enabled_node && false == _enabled_node->getBoolValue() ) {
 150                 // do nothing if lift has been zeroed
 151                 if( strength != 0.0 ) {
 152                         if( strength > 0.1 ) {
 153                                 // slowly fade out strong lifts
 154                                 strength = fgGetLowPass( strength, 0, dt );
 155                         } else {
 156                                 strength = 0.0;
 157                         }
 158                         _ridge_lift_fps_node->setDoubleValue( strength );
 159                 }
 160                 return;
 161         }
 162
 163         timer -= dt;
 164         if (timer <= 0.0 ) {
 165
 166                 // NOTE: this mixes geocentric and geodetic calculations which give mathematically incorrect results
 167                 //       probably this is acceptable for calculating the ridge lift, converting from
 168                 //       geodetic to geocentric coordinates is somewhat expensive
 169
 170                 // probe0 is current position
 171                 probe_lat_deg[0] = _user_latitude_node->getDoubleValue();
 172                 probe_lon_deg[0] = _user_longitude_node->getDoubleValue();
 173                 probe_elev_m[0]  = _ground_elev_node->getDoubleValue() * SG_FEET_TO_METER;
 174
 175                 SGGeoc myPosition = SGGeoc::fromDegM( probe_lon_deg[0], probe_lat_deg[0], 20000.0 );
 176                 double ground_wind_from_rad = _surface_wind_from_deg_node->getDoubleValue() * SG_DEGREES_TO_RADIANS + SG_PI;
 177
 178                 // compute the remaining probes
 179                 for (int i = 1; i < sizeof(probe_lat_deg)/sizeof(probe_lat_deg[0]); i++) {
 180                         SGGeoc probe = myPosition.advanceRadM( ground_wind_from_rad, dist_probe_m[i] );
 181                         probe_lat_deg[i] = probe.getLatitudeDeg();
 182                         probe_lon_deg[i] = probe.getLongitudeDeg();
 183                         if (!globals->get_scenery()->get_elevation_m(
 184                                 SGGeod::fromDegM(probe_lon_deg[i],probe_lat_deg[i], 20000), probe_elev_m[i], NULL )) {
 185                                 // no ground found? use elevation of previous probe :-(
 186                                 probe_elev_m[i] = probe_elev_m[i-1];
 187                         }
 188                 }
 189
 190                 // slopes
 191                 double adj_slope[sizeof(slope)];
 192                 slope[0] = (probe_elev_m[0] - probe_elev_m[1]) / dist_probe_m[1];
 193                 slope[1] = (probe_elev_m[1] - probe_elev_m[2]) / dist_probe_m[2];
 194                 slope[2] = (probe_elev_m[2] - probe_elev_m[3]) / dist_probe_m[3];
 195                 slope[3] = (probe_elev_m[4] - probe_elev_m[0]) / -dist_probe_m[4];
 196
 197                 for (int i = 0; i < sizeof(slope)/sizeof(slope[0]); i++)
 198                         adj_slope[i] = sin(atan(5.0 * pow ( (fabs(slope[i])),1.7) ) ) *sign(slope[i]);
 199
 200                 //adjustment
 201                 adj_slope[0] *= 0.2;
 202                 adj_slope[1] *= 0.2;
 203                 if ( adj_slope [2] < 0.0 ) {
 204                         adj_slope[2] *= 0.5;
 205                 } else {
 206                         adj_slope[2] = 0.0 ;
 207                 }
 208
 209                 if ( ( adj_slope [0] >= 0.0 ) && ( adj_slope [3] < 0.0 ) ) {
 210                         adj_slope[3] = 0.0;
 211                 } else {
 212                         adj_slope[3] *= 0.2;
 213                 }
 214                 lift_factor = adj_slope[0]+adj_slope[1]+adj_slope[2]+adj_slope[3];
 215
 216                 // restart the timer
 217                 timer = 1.0;
 218         }
 219
 220         //user altitude above ground
 221         double user_altitude_agl_m = _user_altitude_agl_ft_node->getDoubleValue() * SG_FEET_TO_METER;
 222
 223         //boundaries
 224         double boundary2_m = 130.0; // in the lift
 225         if (lift_factor < 0.0) { // in the sink
 226                 double highest_probe_temp= max ( probe_elev_m[1], probe_elev_m[2] );
 227                 double highest_probe_downwind_m= max ( highest_probe_temp, probe_elev_m[3] );
 228                 boundary2_m = highest_probe_downwind_m - probe_elev_m[0];
 229         }
 230
 231         double agl_factor;
 232         if ( user_altitude_agl_m < BOUNDARY1_m ) {
 233                 agl_factor = 0.5+0.5*user_altitude_agl_m /BOUNDARY1_m ;
 234         } else if ( user_altitude_agl_m < boundary2_m ) {
 235                 agl_factor = 1.0;
 236         } else {
 237                 agl_factor = exp(-(2 + probe_elev_m[0] / 2000) *
 238                                 (user_altitude_agl_m - boundary2_m) / max(probe_elev_m[0],200.0));
 239         }
 240
 241         double ground_wind_speed_mps = _surface_wind_speed_node->getDoubleValue() * SG_NM_TO_METER / 3600;
 242         double lift_mps = lift_factor* ground_wind_speed_mps * agl_factor;
 243
 244         //the updraft, finally, in ft per second
 245         strength = fgGetLowPass( strength, lift_mps * SG_METER_TO_FEET, dt );
 246         _ridge_lift_fps_node->setDoubleValue( strength );
 247 }