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/****************************************************************************/
/* */
/* ./grid/bng.c - Convert to British Grid */
/* */
/* This file is part of gpstrans - a program to communicate with garmin gps */
/* Parts are taken from John F. Waers (jfwaers@csn.net) program MacGPS. */
/* */
/* */
/* Copyright (c) 1995 by Carsten Tschach (tschach@zedat.fu-berlin.de) */
/* */
/* Permission to use, copy, modify, and distribute this software and its */
/* documentation for non-commercial purpose, is hereby granted without fee, */
/* providing that the copyright notice appear in all copies and that both */
/* the copyright notice and this permission notice appear in supporting */
/* documentation. I make no representations about the suitability of this */
/* software for any purpose. It is provides "as is" without express or */
/* implid warranty. */
/* */
/****************************************************************************/
#include "defs.h"
#include "Garmin.h"
#include <math.h>
/****************************************************************************/
/* The k0 constant was empirically determined to give the best fit to the */
/* data from the GPS 45 and the PCX5 program. It should be 0.9996, but this */
/* number resulted in slight errors in the data. */
/****************************************************************************/
/* define constants */
static const char *zoneID0 = "STUQRNOPLMHJKFGCDEABXYZVW";
static const char *zoneID1 = "VWXYZQRSTULMNOPFGHJKABCDE";
static const double lat0 = 49.0; /* reference transverse mercator latitude */
static const double lon0 = -2.0; /* and longitude */
static const double k0 = 0.99960133;
/****************************************************************************/
/* Convert degree to British Grid Format. */
/****************************************************************************/
void DegToBNG(double lat, double lon, char *zone, double *x, double *y)
{
short X0, Y0, X1, Y1;
strcpy(zone, "--");
toTM(lat, lon, lat0, lon0, k0, x, y);
/* add false easting and northing and round to nearest meter */
*x = floor(*x + 400000.0 + 0.5);
*y = floor(*y - 100000.0 + 0.5);
/* check for invalid range */
if (*x < 0.0 || *x >1.0e6 || *y < 0.0 || *y > 2.5e6) {
/* return with zone = "--" and set x and y to 0.0 */
*x = 0.0;
*y = 0.0;
return;
}
X0 = (long)*x / 500000;
Y0 = (long)*y / 500000;
X1 = ((long)*x / 100000) % 5;
Y1 = ((long)*y / 100000) % 5;
*x = (long)*x % 100000;
*y = (long)*y % 100000;
zone[0] = zoneID0[5 * Y0 + X0];
zone[1] = zoneID1[5 * Y1 + X1];
}
/****************************************************************************/
/* Convert British Grid Format to degree. */
/****************************************************************************/
void BNGtoDeg(char *zone, double x, double y, double *lat, double *lon)
{
int m, n;
/* Check for invalid zone */
if (strcmp(zone, "--") == 0 || x < 0.0 || x > 100000.0 || y < 0.0 ||
y > 100000.0) {
*lat = 0.0;
*lon = 0.0;
return;
}
m = strchr(zoneID0, zone[0]) - zoneID0;
n = strchr(zoneID1, zone[1]) - zoneID1;
x += (m % 5) * 500000.0 + (n % 5) * 100000.0 - 400000.0;
y += (m / 5) * 500000.0 + (n / 5) * 100000.0 + 100000.0;
fromTM(x, y, lat0, lon0, k0, lat, lon);
}
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