545 lines
12 KiB
C
545 lines
12 KiB
C
/* propdelay.c,v 3.1 1993/07/06 01:05:24 jbj Exp
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* propdelay - compute propagation delays
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*
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* cc -o propdelay propdelay.c -lm
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*
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* "Time and Frequency Users' Manual", NBS Technical Note 695 (1977).
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*/
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/*
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* This can be used to get a rough idea of the HF propagation delay
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* between two points (usually between you and the radio station).
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* The usage is
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*
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* propdelay latitudeA longitudeA latitudeB longitudeB
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*
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* where points A and B are the locations in question. You obviously
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* need to know the latitude and longitude of each of the places.
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* The program expects the latitude to be preceded by an 'n' or 's'
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* and the longitude to be preceded by an 'e' or 'w'. It understands
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* either decimal degrees or degrees:minutes:seconds. Thus to compute
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* the delay between the WWVH (21:59:26N, 159:46:00W) and WWV (40:40:49N,
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* 105:02:27W) you could use:
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*
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* propdelay n21:59:26 w159:46 n40:40:49 w105:02:27
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*
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* By default it prints out a summer (F2 average virtual height 350 km) and
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* winter (F2 average virtual height 250 km) number. The results will be
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* quite approximate but are about as good as you can do with HF time anyway.
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* You might pick a number between the values to use, or use the summer
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* value in the summer and switch to the winter value when the static
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* above 10 MHz starts to drop off in the fall. You can also use the
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* -h switch if you want to specify your own virtual height.
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*
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* You can also do a
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*
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* propdelay -W n45:17:47 w75:45:22
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*
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* to find the propagation delays to WWV and WWVH (from CHU in this
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* case), a
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*
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* propdelay -C n40:40:49 w105:02:27
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*
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* to find the delays to CHU, and a
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*
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* propdelay -G n52:03:17 w98:34:18
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*
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* to find delays to GOES via each of the three satellites.
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*/
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#include <stdio.h>
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#include <string.h>
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#include "ntp_stdlib.h"
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extern double sin (double);
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extern double cos (double);
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extern double acos (double);
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extern double tan (double);
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extern double atan (double);
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extern double sqrt (double);
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#define STREQ(a, b) (*(a) == *(b) && strcmp((a), (b)) == 0)
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/*
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* Program constants
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*/
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#define EARTHRADIUS (6370.0) /* raduis of earth (km) */
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#define LIGHTSPEED (299800.0) /* speed of light, km/s */
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#define PI (3.1415926536)
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#define RADPERDEG (PI/180.0) /* radians per degree */
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#define MILE (1.609344) /* km in a mile */
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#define SUMMERHEIGHT (350.0) /* summer height in km */
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#define WINTERHEIGHT (250.0) /* winter height in km */
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#define SATHEIGHT (6.6110 * 6378.0) /* geosync satellite height in km
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from centre of earth */
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#define WWVLAT "n40:40:49"
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#define WWVLONG "w105:02:27"
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#define WWVHLAT "n21:59:26"
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#define WWVHLONG "w159:46:00"
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#define CHULAT "n45:17:47"
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#define CHULONG "w75:45:22"
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#define GOES_UP_LAT "n37:52:00"
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#define GOES_UP_LONG "w75:27:00"
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#define GOES_EAST_LONG "w75:00:00"
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#define GOES_STBY_LONG "w105:00:00"
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#define GOES_WEST_LONG "w135:00:00"
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#define GOES_SAT_LAT "n00:00:00"
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char *wwvlat = WWVLAT;
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char *wwvlong = WWVLONG;
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char *wwvhlat = WWVHLAT;
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char *wwvhlong = WWVHLONG;
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char *chulat = CHULAT;
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char *chulong = CHULONG;
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char *goes_up_lat = GOES_UP_LAT;
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char *goes_up_long = GOES_UP_LONG;
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char *goes_east_long = GOES_EAST_LONG;
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char *goes_stby_long = GOES_STBY_LONG;
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char *goes_west_long = GOES_WEST_LONG;
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char *goes_sat_lat = GOES_SAT_LAT;
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int hflag = 0;
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int Wflag = 0;
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int Cflag = 0;
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int Gflag = 0;
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int height;
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char *progname;
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int debug;
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static void doit (double, double, double, double, double, char *);
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static double latlong (char *, int);
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static double greatcircle (double, double, double, double);
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static double waveangle (double, double, int);
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static double propdelay (double, double, int);
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static int finddelay (double, double, double, double, double, double *);
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static void satdoit (double, double, double, double, double, double, char *);
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static void satfinddelay (double, double, double, double, double *);
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static double satpropdelay (double);
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/*
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* main - parse arguments and handle options
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*/
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int
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main(
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int argc,
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char *argv[]
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)
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{
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int c;
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int errflg = 0;
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double lat1, long1;
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double lat2, long2;
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double lat3, long3;
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progname = argv[0];
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while ((c = ntp_getopt(argc, argv, "dh:CWG")) != EOF)
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switch (c) {
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case 'd':
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++debug;
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break;
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case 'h':
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hflag++;
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height = atof(ntp_optarg);
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if (height <= 0.0) {
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(void) fprintf(stderr, "height %s unlikely\n",
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ntp_optarg);
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errflg++;
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}
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break;
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case 'C':
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Cflag++;
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break;
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case 'W':
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Wflag++;
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break;
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case 'G':
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Gflag++;
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break;
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default:
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errflg++;
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break;
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}
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if (errflg || (!(Cflag || Wflag || Gflag) && ntp_optind+4 != argc) ||
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((Cflag || Wflag || Gflag) && ntp_optind+2 != argc)) {
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(void) fprintf(stderr,
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"usage: %s [-d] [-h height] lat1 long1 lat2 long2\n",
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progname);
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(void) fprintf(stderr," - or -\n");
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(void) fprintf(stderr,
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"usage: %s -CWG [-d] lat long\n",
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progname);
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exit(2);
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}
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if (!(Cflag || Wflag || Gflag)) {
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lat1 = latlong(argv[ntp_optind], 1);
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long1 = latlong(argv[ntp_optind + 1], 0);
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lat2 = latlong(argv[ntp_optind + 2], 1);
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long2 = latlong(argv[ntp_optind + 3], 0);
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if (hflag) {
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doit(lat1, long1, lat2, long2, height, "");
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} else {
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doit(lat1, long1, lat2, long2, (double)SUMMERHEIGHT,
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"summer propagation, ");
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doit(lat1, long1, lat2, long2, (double)WINTERHEIGHT,
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"winter propagation, ");
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}
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} else if (Wflag) {
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/*
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* Compute delay from WWV
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*/
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lat1 = latlong(argv[ntp_optind], 1);
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long1 = latlong(argv[ntp_optind + 1], 0);
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lat2 = latlong(wwvlat, 1);
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long2 = latlong(wwvlong, 0);
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if (hflag) {
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doit(lat1, long1, lat2, long2, height, "WWV ");
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} else {
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doit(lat1, long1, lat2, long2, (double)SUMMERHEIGHT,
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"WWV summer propagation, ");
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doit(lat1, long1, lat2, long2, (double)WINTERHEIGHT,
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"WWV winter propagation, ");
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}
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/*
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* Compute delay from WWVH
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*/
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lat2 = latlong(wwvhlat, 1);
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long2 = latlong(wwvhlong, 0);
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if (hflag) {
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doit(lat1, long1, lat2, long2, height, "WWVH ");
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} else {
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doit(lat1, long1, lat2, long2, (double)SUMMERHEIGHT,
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"WWVH summer propagation, ");
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doit(lat1, long1, lat2, long2, (double)WINTERHEIGHT,
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"WWVH winter propagation, ");
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}
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} else if (Cflag) {
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lat1 = latlong(argv[ntp_optind], 1);
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long1 = latlong(argv[ntp_optind + 1], 0);
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lat2 = latlong(chulat, 1);
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long2 = latlong(chulong, 0);
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if (hflag) {
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doit(lat1, long1, lat2, long2, height, "CHU ");
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} else {
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doit(lat1, long1, lat2, long2, (double)SUMMERHEIGHT,
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"CHU summer propagation, ");
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doit(lat1, long1, lat2, long2, (double)WINTERHEIGHT,
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"CHU winter propagation, ");
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}
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} else if (Gflag) {
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lat1 = latlong(goes_up_lat, 1);
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long1 = latlong(goes_up_long, 0);
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lat3 = latlong(argv[ntp_optind], 1);
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long3 = latlong(argv[ntp_optind + 1], 0);
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lat2 = latlong(goes_sat_lat, 1);
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long2 = latlong(goes_west_long, 0);
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satdoit(lat1, long1, lat2, long2, lat3, long3,
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"GOES Delay via WEST");
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long2 = latlong(goes_stby_long, 0);
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satdoit(lat1, long1, lat2, long2, lat3, long3,
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"GOES Delay via STBY");
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long2 = latlong(goes_east_long, 0);
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satdoit(lat1, long1, lat2, long2, lat3, long3,
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"GOES Delay via EAST");
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}
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exit(0);
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}
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/*
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* doit - compute a delay and print it
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*/
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static void
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doit(
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double lat1,
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double long1,
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double lat2,
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double long2,
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double h,
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char *str
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)
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{
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int hops;
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double delay;
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hops = finddelay(lat1, long1, lat2, long2, h, &delay);
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printf("%sheight %g km, hops %d, delay %g seconds\n",
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str, h, hops, delay);
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}
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/*
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* latlong - decode a latitude/longitude value
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*/
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static double
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latlong(
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char *str,
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int islat
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)
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{
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register char *cp;
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register char *bp;
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double arg;
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double div;
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int isneg;
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char buf[32];
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char *colon;
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if (islat) {
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/*
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* Must be north or south
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*/
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if (*str == 'N' || *str == 'n')
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isneg = 0;
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else if (*str == 'S' || *str == 's')
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isneg = 1;
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else
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isneg = -1;
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} else {
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/*
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* East is positive, west is negative
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*/
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if (*str == 'E' || *str == 'e')
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isneg = 0;
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else if (*str == 'W' || *str == 'w')
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isneg = 1;
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else
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isneg = -1;
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}
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if (isneg >= 0)
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str++;
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colon = strchr(str, ':');
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if (colon != NULL) {
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/*
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* in hhh:mm:ss form
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*/
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cp = str;
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bp = buf;
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while (cp < colon)
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*bp++ = *cp++;
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*bp = '\0';
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cp++;
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arg = atof(buf);
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div = 60.0;
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colon = strchr(cp, ':');
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if (colon != NULL) {
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bp = buf;
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while (cp < colon)
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*bp++ = *cp++;
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*bp = '\0';
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cp++;
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arg += atof(buf) / div;
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div = 3600.0;
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}
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if (*cp != '\0')
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arg += atof(cp) / div;
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} else {
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arg = atof(str);
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}
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if (isneg == 1)
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arg = -arg;
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if (debug > 2)
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(void) printf("latitude/longitude %s = %g\n", str, arg);
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return arg;
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}
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/*
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* greatcircle - compute the great circle distance in kilometers
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*/
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static double
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greatcircle(
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double lat1,
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double long1,
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double lat2,
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double long2
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)
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{
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double dg;
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double l1r, l2r;
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l1r = lat1 * RADPERDEG;
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l2r = lat2 * RADPERDEG;
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dg = EARTHRADIUS * acos(
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(cos(l1r) * cos(l2r) * cos((long2-long1)*RADPERDEG))
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+ (sin(l1r) * sin(l2r)));
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if (debug >= 2)
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printf(
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"greatcircle lat1 %g long1 %g lat2 %g long2 %g dist %g\n",
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lat1, long1, lat2, long2, dg);
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return dg;
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}
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/*
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* waveangle - compute the wave angle for the given distance, virtual
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* height and number of hops.
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*/
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static double
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waveangle(
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double dg,
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double h,
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int n
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)
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{
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double theta;
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double delta;
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theta = dg / (EARTHRADIUS * (double)(2 * n));
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delta = atan((h / (EARTHRADIUS * sin(theta))) + tan(theta/2)) - theta;
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if (debug >= 2)
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printf("waveangle dist %g height %g hops %d angle %g\n",
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dg, h, n, delta / RADPERDEG);
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return delta;
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}
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/*
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* propdelay - compute the propagation delay
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*/
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static double
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propdelay(
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double dg,
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double h,
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int n
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)
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{
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double phi;
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double theta;
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double td;
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theta = dg / (EARTHRADIUS * (double)(2 * n));
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phi = (PI/2.0) - atan((h / (EARTHRADIUS * sin(theta))) + tan(theta/2));
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td = dg / (LIGHTSPEED * sin(phi));
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if (debug >= 2)
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printf("propdelay dist %g height %g hops %d time %g\n",
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dg, h, n, td);
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return td;
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}
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/*
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* finddelay - find the propagation delay
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*/
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static int
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finddelay(
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double lat1,
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double long1,
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double lat2,
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double long2,
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double h,
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double *delay
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)
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{
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double dg; /* great circle distance */
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double delta; /* wave angle */
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int n; /* number of hops */
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dg = greatcircle(lat1, long1, lat2, long2);
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if (debug)
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printf("great circle distance %g km %g miles\n", dg, dg/MILE);
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n = 1;
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while ((delta = waveangle(dg, h, n)) < 0.0) {
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if (debug)
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printf("tried %d hop%s, no good\n", n, n>1?"s":"");
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n++;
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}
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if (debug)
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printf("%d hop%s okay, wave angle is %g\n", n, n>1?"s":"",
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delta / RADPERDEG);
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*delay = propdelay(dg, h, n);
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return n;
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}
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/*
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* satdoit - compute a delay and print it
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*/
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static void
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satdoit(
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double lat1,
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double long1,
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double lat2,
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double long2,
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double lat3,
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double long3,
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char *str
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)
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{
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double up_delay,down_delay;
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satfinddelay(lat1, long1, lat2, long2, &up_delay);
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satfinddelay(lat3, long3, lat2, long2, &down_delay);
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printf("%s, delay %g seconds\n", str, up_delay + down_delay);
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}
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/*
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* satfinddelay - calculate the one-way delay time between a ground station
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* and a satellite
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*/
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static void
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satfinddelay(
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double lat1,
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double long1,
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double lat2,
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double long2,
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double *delay
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)
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{
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double dg; /* great circle distance */
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dg = greatcircle(lat1, long1, lat2, long2);
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*delay = satpropdelay(dg);
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}
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/*
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* satpropdelay - calculate the one-way delay time between a ground station
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* and a satellite
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*/
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static double
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satpropdelay(
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double dg
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)
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{
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double k1, k2, dist;
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double theta;
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double td;
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theta = dg / (EARTHRADIUS);
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k1 = EARTHRADIUS * sin(theta);
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k2 = SATHEIGHT - (EARTHRADIUS * cos(theta));
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if (debug >= 2)
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printf("Theta %g k1 %g k2 %g\n", theta, k1, k2);
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dist = sqrt(k1*k1 + k2*k2);
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td = dist / LIGHTSPEED;
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if (debug >= 2)
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printf("propdelay dist %g height %g time %g\n", dg, dist, td);
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return td;
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|
}
|