# Dronaldo17/ChinaMapShift

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 // // china_shift.c // // Most code created by someone anonymous. Thank you, someone. // transformFromGCJToWGS() added by Fengzee (fengzee@fengzee.com). // #include "china_shift.h" #include Location LocationMake(double lng, double lat) { Location loc; loc.lng = lng, loc.lat = lat; return loc; } /// /// Transform WGS-84 to GCJ-02 (Chinese encrypted coordination system) /// const double pi = 3.14159265358979324; // // Krasovsky 1940 // // a = 6378245.0, 1/f = 298.3 // b = a * (1 - f) // ee = (a^2 - b^2) / a^2; const double a = 6378245.0; const double ee = 0.00669342162296594323; int outOfChina(double lat, double lon) { if (lon < 72.004 || lon > 137.8347) return 1; if (lat < 0.8293 || lat > 55.8271) return 1; return 0; } double transformLat(double x, double y) { double ret = -100.0 + 2.0 * x + 3.0 * y + 0.2 * y * y + 0.1 * x * y + 0.2 * sqrt(x > 0 ? x:-x); ret += (20.0 * sin(6.0 * x * pi) + 20.0 *sin(2.0 * x * pi)) * 2.0 / 3.0; ret += (20.0 * sin(y * pi) + 40.0 * sin(y / 3.0 * pi)) * 2.0 / 3.0; ret += (160.0 * sin(y / 12.0 * pi) + 320 * sin(y * pi / 30.0)) * 2.0 / 3.0; return ret; } double transformLon(double x, double y) { double ret = 300.0 + x + 2.0 * y + 0.1 * x * x + 0.1 * x * y + 0.1 * sqrt(x > 0 ? x:-x); ret += (20.0 * sin(6.0 * x * pi) + 20.0 * sin(2.0 * x * pi)) * 2.0 / 3.0; ret += (20.0 * sin(x * pi) + 40.0 * sin(x / 3.0 * pi)) * 2.0 / 3.0; ret += (150.0 * sin(x / 12.0 * pi) + 300.0 * sin(x / 30.0 * pi)) * 2.0 / 3.0; return ret; } Location transformFromWGSToGCJ(Location wgLoc) { Location mgLoc; if (outOfChina(wgLoc.lat, wgLoc.lng)) { mgLoc = wgLoc; return mgLoc; } double dLat = transformLat(wgLoc.lng - 105.0, wgLoc.lat - 35.0); double dLon = transformLon(wgLoc.lng - 105.0, wgLoc.lat - 35.0); double radLat = wgLoc.lat / 180.0 * pi; double magic = sin(radLat); magic = 1 - ee * magic * magic; double sqrtMagic = sqrt(magic); dLat = (dLat * 180.0) / ((a * (1 - ee)) / (magic * sqrtMagic) * pi); dLon = (dLon * 180.0) / (a / sqrtMagic * cos(radLat) * pi); mgLoc.lat = wgLoc.lat + dLat; mgLoc.lng = wgLoc.lng + dLon; return mgLoc; } /// /// Transform GCJ-02 to WGS-84 /// Reverse of transformFromWGSToGC() by iteration. /// /// Created by Fengzee (fengzee@fengzee.me). /// Location transformFromGCJToWGS(Location gcLoc) { Location wgLoc = gcLoc; Location currGcLoc, dLoc; while (1) { currGcLoc = transformFromWGSToGCJ(wgLoc); dLoc.lat = gcLoc.lat - currGcLoc.lat; dLoc.lng = gcLoc.lng - currGcLoc.lng; if (fabs(dLoc.lat) < 1e-7 && fabs(dLoc.lng) < 1e-7) { // 1e-7 ~ centimeter level accuracy // Result of experiment: // Most of the time 2 iterations would be enough for an 1e-8 accuracy (milimeter level). // return wgLoc; } wgLoc.lat += dLoc.lat; wgLoc.lng += dLoc.lng; } return wgLoc; } /// /// Transform GCJ-02 to BD-09 /// const double x_pi = 3.14159265358979324 * 3000.0 / 180.0; Location bd_encrypt(Location gcLoc) { double x = gcLoc.lng, y = gcLoc.lat; double z = sqrt(x * x + y * y) + 0.00002 * sin(y * x_pi); double theta = atan2(y, x) + 0.000003 * cos(x * x_pi); return LocationMake(z * cos(theta) + 0.0065, z * sin(theta) + 0.006); } /// /// Transform BD-09 to GCJ-02 /// Location bd_decrypt(Location bdLoc) { double x = bdLoc.lng - 0.0065, y = bdLoc.lat - 0.006; double z = sqrt(x * x + y * y) - 0.00002 * sin(y * x_pi); double theta = atan2(y, x) - 0.000003 * cos(x * x_pi); return LocationMake(z * cos(theta), z * sin(theta)); }