/** * \file src/locator.c * \ingroup hamlib * \brief locator and bearing conversion interface * \author Stephane Fillod * \date 2000-2002 * * Hamlib Interface - locator and bearing conversion calls */ /* * Hamlib Interface - locator and bearing conversion calls * Copyright (c) 2001-2002 by Stephane Fillod * Copyright (c) 2003 by Nate Bargmann * * $Id: locator.c,v 1.7 2003-08-19 23:41:08 n0nb Exp $ * * Code to determine bearing and range was taken from the Great Circle, * by S. R. Sampson, N5OWK. * Ref: "Air Navigation", Air Force Manual 51-40, 1 February 1987 * Ref: "ARRL Satellite Experimenters Handbook", August 1990 * * Code to calculate distance and azimuth between two Maidenhead locators, * taken from wwl, by IK0ZSN Mirko Caserta. * * * This library is free software; you can redistribute it and/or modify * it under the terms of the GNU Library General Public License as * published by the Free Software Foundation; either version 2 of * the License, or (at your option) any later version. * * This program 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 Library General Public License for more details. * * You should have received a copy of the GNU Library General Public * License along with this library; if not, write to the Free Software * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. * */ /*! \page hamlib Hamlib general purpose API * * Here are grouped some often used functions, like locator conversion * routines. */ #ifdef HAVE_CONFIG_H #include "config.h" #endif #include #include #include #include #include #include #ifndef DOC_HIDDEN #define RADIAN (180.0 / M_PI) /* arc length for 1 degree, 60 Nautical Miles */ #define ARC_IN_KM 111.2 #endif /* !DOC_HIDDEN */ /** * \brief Convert DMS angle to decimal representation * \param degrees Degrees * \param minutes Minutes * \param seconds Seconds * * Convert degree/minute/second angle to a decimal representation. * Degrees >360, minutes > 60, and seconds > 60 are allowed, but * resulting angle won't be normalized. * * \return the decimal representation. * * \sa dec2dms() */ double dms2dec(int degrees, int minutes, int seconds) { if (degrees >= 0) return (double)degrees + (double)minutes/60. + (double)seconds/3600.; else return (double)degrees - (double)minutes/60. - (double)seconds/3600.; } /** * \brief Convert decimal angle into DMS representation * \param dec Decimal angle * \param degrees The location where to store the degrees * \param minutes The location where to store the minutes * \param seconds The location where to store the seconds * * Convert decimal angle into its degree/minute/second representation. * * When passed a value < -180 or > 180, the sign will be reversed * and the value constrained to => -180 and <= 180 before conversion. * * Upon return dec2dms guarantees -180<=degrees<180, * 0<=minutes<60, and 0<=seconds<60. * * \sa dms2dec() */ void dec2dms(double dec, int *degrees, int *minutes, int *seconds) { int deg, min, sec, is_neg = 0; double st; if (!degrees || !minutes || !seconds) return; /* reverse the sign if dec has a magnitude greater * than 180 and factor out multiples of 360. * e.g. when passed 270 st will be set to -90 * and when passed -270 st will be set to 90. If * passed 361 st will be set to -1, etc. If passed * a value > -180 || < 180, value will be unchanged. */ if (dec >= 0.0) st = fmod(dec + 180, 360) - 180; else st = fmod(dec - 180, 360) + 180; /* if after all of that st is negative, we want deg * to be negative as well. Treat -180 as a special * case, not returning its sign so longitudes will * be returned from -179.999 to 180.0. */ if (st < 0.0 && st != -180.) is_neg = 1; /* work on st as a positive value to remove a * bug introduced by the effect of floor() when * passed a negative value. e.g. when passed * -96.8333 floor() returns -95! Also avoids * a rounding error introduced on negative values. */ st = fabs(st); deg = (int)floor(st); st = 60. * (st-(double)deg); min = (int)floor(st); st = 60. * (st-(double)min); sec = (int)floor(st); /* round fractional seconds up if greater than sec.5 * round up min and deg if warranted. */ if (fmod(st, sec) >= 0.5) { sec++; if (sec == 60) { sec = 0; min++; if (min == 60) { min = 0; deg++; } } } /* set *degrees to original sign passed to dec */ (is_neg == 1) ? (*degrees = deg * -1) : (*degrees = deg); *minutes = min; *seconds = sec; } /** * \brief Convert Maidenhead grid locator to longitude/latitude * \param longitude The location where to store longitude, decimal * \param latitude The location where to store latitude, decimal * \param locator The locator--four or six char nul terminated string * * Convert Maidenhead grid locator to longitude/latitude (decimal). * The locator be either in 4 or 6 chars long format. locator2longlat * is case insensitive, however it checks for locator validity. * * Decimal long/lat is computed to center of grid square, i.e. given * EM19 will return coordinates equivalent to the southwest corner * of EM19mm. Given a six character locator, computed values will * in the center of the given subsquare, i.e. 2' 30" from west boundary * and 1' 15" from south boundary. * * \todo Support for greater accuracy as proposed by Dave Hines to * six pairs of grid designators. * * \return RIG_OK to indicate conversion went ok, -RIG_EINVAL if locator * exceeds RR99xx or is malformed (not of 4 or 6 character format). * * \sa longlat2locator() */ int locator2longlat(double *longitude, double *latitude, const char *locator) { char loc[6]; int length; if (locator[4] != '\0' && locator[6] != '\0') return -RIG_EINVAL; loc[0] = toupper(locator[0]); loc[1] = toupper(locator[1]); loc[2] = locator[2]; loc[3] = locator[3]; if (locator[4] != '\0') { loc[4] = toupper(locator[4]); loc[5] = toupper(locator[5]); length = 6; } else { /* center of 4 character grid */ loc[4] = 'M'; loc[5] = 'M'; length = 4; } if (loc[0] < 'A' || loc[0] > 'R' || loc[1] < 'A' || loc[1] > 'R' || loc[2] < '0' || loc[2] > '9' || loc[3] < '0' || loc[3] > '9' || loc[4] < 'A' || loc[4] > 'X' || loc[5] < 'A' || loc[5] > 'X' ) { return -RIG_EINVAL; } *longitude = 20.0 * (loc[0]-'A') - 180.0 + 2.0 * (loc[2]-'0') + (loc[4]-'A')/12.0; /* move east to center of subsquare */ if (length == 6) *longitude += 0.04166666; *latitude = 10.0 * (loc[1]-'A') - 90.0 + (loc[3]-'0') + (loc[5]-'A')/24.0; /* move north to center of subsquare */ if (length == 6) *latitude += 0.020833333; return RIG_OK; } /** * \brief Convert longitude/latitude to Maidenhead grid locator * \param longitude The longitude, decimal * \param latitude The latitude, decimal * \param locator The location where to store the locator * * Convert longitude/latitude (decimal) to Maidenhead grid locator. * \a locator must point to an array at least 6 char long. * * \todo Support for greater accuracy as proposed by Dave Hines to * six pairs of grid designators. * * \sa locator2longlat() */ void longlat2locator(double longitude, double latitude, char *locator) { double tmp, min_sec; tmp = longitude; /* Ideally, the input should be constrained to * >= -180. && < 179.9999999999999 */ if (tmp == 180.) tmp = -tmp; /* with input of -180 to 179 this expression will evaluate * to 1 to 359 or degrees east of -180 degrees longitude. */ tmp = fmod(tmp, 360) + 180.; /* determine west side of the field. Fields always start at * a longitude that is a multiple of 20. Fields advance * eastward from -180 deg West longitude. */ locator[0] = 'A' + (int)floor(tmp/20.); tmp = fmod(tmp, 20.); /* at this point tmp = degrees east of west boundary * of the field. */ locator[2] = '0' + (int)floor(tmp/2.); min_sec = 12. * fabs(floor(longitude)-longitude); /* When tmp is an odd value, then we must be sure that * the subsquare is referenced to 'm' as the longitude * subsquare range spans 2 degrees. */ if ((int)tmp % 2) locator[4] = 'm' + (int)floor(min_sec); else locator[4] = 'a' + (int)floor(min_sec); /* input should be constrained to >= -90. && < 90. */ tmp = fmod(latitude, 360) + 90.; locator[1] = 'A' + (int)floor(tmp/10.); tmp = fmod(tmp, 10.); locator[3] = '0' + (int)floor(tmp); tmp = 24. * fabs(floor(latitude)-latitude); locator[5] = 'a' + (int)floor(tmp); } /** * \brief Calculate the distance and bearing between two points. * \param lon1 The local longitude, decimal degrees * \param lat1 The local latitude, decimal degrees * \param lon2 The remote longitude, decimal degrees * \param lat2 The remote latitude, decimal degrees * \param distance The location where to store the distance * \param azimuth The location where to store the bearing * * Calculate the QRB between \a lat1,\a lat1 and \a lon2,\a lat2. * * This version also takes into consideration the two points * being close enough to be in the near-field, and the antipodal points, * which are easily calculated. * * \return the distance in kilometers and azimuth in decimal degrees * for the short path. * * \sa distance_long_path(), azimuth_long_path() */ int qrb(double lon1, double lat1, double lon2, double lat2, double *distance, double *azimuth) { double delta_long, tmp, arc, cosaz, az; if (!distance || !azimuth) return -1; if ((lat1 > 90.0 || lat1 < -90.0) || (lat2 > 90.0 || lat2 < -90.0)) return -1; if ((lon1 > 180.0 || lon1 < -180.0) || (lon2 > 180.0 || lon2 < -180.0)) return -1; /* Prevent ACOS() Domain Error */ if (lat1 == 90.0) lat1 = 89.99; else if (lat1 == -90.0) lat1 = -89.99; if (lat2 == 90.0) lat2 = 89.99; else if (lat2 == -90.0) lat2 = -89.99; /* * Convert variables to Radians */ lat1 /= RADIAN; lon1 /= RADIAN; lat2 /= RADIAN; lon2 /= RADIAN; delta_long = lon2 - lon1; tmp = sin(lat1) * sin(lat2) + cos(lat1) * cos(lat2) * cos(delta_long); if (tmp > .999999) { /* Station points coincide, use an Omni! */ *distance = 0.0; *azimuth = 0.0; return 0; } if (tmp < -.999999) { /* * points are antipodal, it's straight down. * Station is equal distance in all Azimuths. * So take 180 Degrees of arc times 60 nm, * and you get 10800 nm, or whatever units... */ *distance = 180.0 * ARC_IN_KM; *azimuth = 0.0; return 0; } arc = acos(tmp); /* * One degree of arc is 60 Nautical miles * at the surface of the earth, 111.2 km, or 69.1 sm * This method is easier than the one in the handbook */ /* Short Path */ *distance = ARC_IN_KM * RADIAN * arc; /* * Long Path * * distlp = (ARC_IN_KM * 360.0) - distsp; */ cosaz = (sin(lat2) - (sin(lat1) * cos(arc))) / (sin(arc) * cos(lat1)); if (cosaz > .999999) az = 0.0; else if (cosaz < -.999999) az = 180.0; else az = acos(cosaz) * RADIAN; /* * Handbook had the test ">= 0.0" which looks backwards?? * must've been frontwards since the numbers seem to make sense * now. ;-) -N0NB */ // if (sin(delta_long) < 0.0) { if (sin(delta_long) >= 0.0) { *azimuth = az; } else { *azimuth = 360.0 - az; } if (*azimuth == 360.0) *azimuth = 0; return 0; } /** * \brief Calculate the long path distance between two points. * \param distance The distance * * Calculate the long path (resp. short path) of a given distance. * * \return the distance in kilometers for the opposite path. * * \sa qrb() */ double distance_long_path(double distance) { return (ARC_IN_KM * 360.0) - distance; } /** * \brief Calculate the long path bearing between two points. * \param azimuth The bearing * * Calculate the long path (resp. short path) of a given bearing. * * \return the azimuth in decimal degrees for the opposite path. * * \sa qrb() */ double azimuth_long_path(double azimuth) { return 360.0 - azimuth; }