test/src/ArcApprox.cpp

   1 /*
   2 Copyright_License {
   3
   4   XCSoar Glide Computer - http://www.xcsoar.org/
   5   Copyright (C) 2000-2013 The XCSoar Project
   6   A detailed list of copyright holders can be found in the file "AUTHORS".
   7
   8   This program is free software; you can redistribute it and/or
   9   modify it under the terms of the GNU General Public License
  10   as published by the Free Software Foundation; either version 2
  11   of the License, or (at your option) any later version.
  12
  13   This program is distributed in the hope that it will be useful,
  14   but WITHOUT ANY WARRANTY; without even the implied warranty of
  15   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16   GNU General Public License for more details.
  17
  18   You should have received a copy of the GNU General Public License
  19   along with this program; if not, write to the Free Software
  20   Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
  21 }
  22 */
  23
  24 #include "OS/Args.hpp"
  25 #include "Geo/GeoPoint.hpp"
  26 #include "Geo/Math.hpp"
  27
  28 #include <stdio.h>
  29
  30 static void
  31 AppendArc(std::vector<GeoPoint> &points, GeoPoint center,
  32           fixed radius, fixed _step)
  33 {
  34   Angle start = Angle::Zero();
  35   Angle end = Angle::HalfCircle();
  36
  37   // 5 or -5, depending on direction
  38   const Angle step = Angle::Degrees(_step);
  39
  40   // Add first polygon point
  41   points.push_back(FindLatitudeLongitude(center, start, radius));
  42
  43   // Add intermediate polygon points
  44   while ((end - start).AbsoluteDegrees() > _step * 3 / 2) {
  45     start = (start + step).AsBearing();
  46     points.push_back(FindLatitudeLongitude(center, start, radius));
  47   }
  48
  49   // Add last polygon point
  50   points.push_back(FindLatitudeLongitude(center, end, radius));
  51 }
  52
  53 static void
  54 TestApproximation(fixed radius, fixed step)
  55 {
  56   GeoPoint center(Angle::Degrees(7), Angle::Degrees(51));
  57
  58   std::vector<GeoPoint> points;
  59   AppendArc(points, center, radius, step);
  60
  61   printf("Number of points: %u\n\n", (unsigned)points.size());
  62
  63   fixed max_error = fixed(0);
  64
  65   for (auto it = points.begin(), it_last = it++, it_end = points.end();
  66       it != it_end; it_last = it++) {
  67     for (fixed x = fixed(0); x < fixed(1); x += fixed(0.1)) {
  68       GeoPoint test_point = (*it_last).Interpolate(*it, x);
  69       fixed distance = center.Distance(test_point);
  70       fixed error = fabs(radius - distance);
  71       if (error > max_error)
  72         max_error = error;
  73     }
  74   }
  75
  76   printf("Max. Error: %f m\n", (double)max_error);
  77 }
  78
  79 int main(int argc, char **argv)
  80 {
  81   Args args(argc, argv, "RADIUS [DEGREE STEPWIDTH = 5]");
  82
  83   fixed radius = fixed(args.ExpectNextInt());
  84   fixed step = fixed(args.IsEmpty() ? 5 : args.ExpectNextDouble());
  85
  86   printf("Airspace Arc Approximation\n\nRadius: %.0f m\nDegree Stepwith: %f deg\n\n",
  87          (double)radius, (double)step);
  88
  89   TestApproximation(radius, step);
  90
  91   return 0;
  92 }