坐标系问题

[firefly11]

百度地图拥有自己的坐标系，大部分使用者的Geojson中坐标点并不是百度坐标系下的，我觉得这是一个很大的问题。如果能够提供不同坐标系转到百度坐标系的接口，精度不用太高。这样的话，可能会有更多使用者。鄙人愚见，恐有不当，见谅。

[wxk6b1203]

百度地图的是墨卡托坐标么？如果这样，经过转换就可以了。eg：

#include <math.h>
#include <stdio.h>
typedef struct {
    double x;
    double y;
} MC;

MC convertLL2MC(double longitude, double latitude);

static MC result = {0, 0};

double getRange(double cf, double ce, double t) {
    if (ce != 0) {
        cf = cf > ce ? cf : ce;
    }
    if (t != 0) {
        cf = cf > t ? t : cf;
    }
    return cf;
}

double getLoop(double cf, double ce, double t) {
    while (cf > t) {
        cf -= t - ce;
    }
    while (cf < ce) {
        cf += t - ce;
    }
    return cf;
}

void convertor(double longitude, double latitude, double *cg) {
    if (!cg) {
        return;
    }
    double t = cg[0] + cg[1] * longitude;
    double ce = fabs(latitude) / cg[9];
    double ch = cg[2] + cg[3] * ce + cg[4] * pow(ce, 2) + cg[5] * pow(ce, 3) +
                cg[6] * pow(ce, 4) + cg[7] * pow(ce, 5) + cg[8] * pow(ce, 6);
    t *= (longitude < 0 ? -1 : 1);
    ch *= (latitude < 0 ? -1 : 1);
    result.x = round(t * 100) / 100;
    result.y = round(ch * 100) / 100;
}

MC convertLL2MC(double longitude, double latitude) {
    int LLBAND[] = {75, 60, 45, 30, 15, 0};
    double LL2MC[][10] = {
        {-0.0015702102444, 111320.7020616939, 1704480524535203,
         -10338987376042340, 26112667856603880, -35149669176653700,
         26595700718403920, -10725012454188240, 1800819912950474, 82.5},
        {0.0008277824516172526, 111320.7020463578, 647795574.6671607,
         -4082003173.641316, 10774905663.51142, -15171875531.51559,
         12053065338.62167, -5124939663.577472, 913311935.9512032, 67.5},
        {0.00337398766765, 111320.7020202162, 4481351.045890365,
         -23393751.19931662, 79682215.47186455, -115964993.2797253,
         97236711.15602145, -43661946.33752821, 8477230.501135234, 52.5},
        {0.00220636496208, 111320.7020209128, 51751.86112841131,
         3796837.749470245, 992013.7397791013, -1221952.21711287,
         1340652.697009075, -620943.6990984312, 144416.9293806241, 37.5},
        {-0.0003441963504368392, 111320.7020576856, 278.2353980772752,
         2485758.690035394, 6070.750963243378, 54821.18345352118,
         9540.606633304236, -2710.55326746645, 1405.483844121726, 22.5},
        {-0.0003218135878613132, 111320.7020701615, 0.00369383431289,
         823725.6402795718, 0.46104986909093, 2351.343141331292,
         1.58060784298199, 8.77738589078284, 0.37238884252424, 7.45}};
    longitude = getLoop(longitude, -180, 180);
    latitude = getRange(latitude, -74, 74);

    int countLLBAND = sizeof(LLBAND) / sizeof(int);
    double *cg = NULL;
    for (int cf = 0; cf < countLLBAND; cf++) {
        if (latitude >= LLBAND[cf]) {
            cg = LL2MC[cf];
            break;
        }
    }
    if (!cg) {
        for (int cf = countLLBAND - 1; cf >= 0; cf--) {
            if (longitude <= -LLBAND[cf]) {
                cg = LL2MC[cf];
                break;
            }
        }
    }

    convertor(longitude, latitude, cg);
    return result;
}

int main(int argc, char const *argv[]) {
    MC a;
    a = convertLL2MC(113.767619, 23.050721);
    printf("%0.2f, %0.2f\n", a.x, a.y);
    return 0;
}

转换的道理不是很懂，但好像确实是这样。

[fengluhome]

@wxk6b1203 墨卡托是投影方式，就是把球面坐标投影到一个平面上，得到的是平面坐标，单位是像素。经纬度坐标要正确的显示屏幕上需要一层墨卡托转换。 BD09：为百度坐标系，在GCJ02坐标系基础上再次加密。其中bd09ll表示百度经纬度坐标，bd09mc表示百度墨卡托米制坐标。详细链接 http://lbsyun.baidu.com/index.php?title=coordinate

[fengluhome]

@firefly11 你的提议很赞，后续官网会加上这个功能，完善周边生态。这有一个开源库可以帮你完成这件事情。地址：https://github.com/wandergis/coordtransform

[fengluhome]

官网增加了坐标系转换http://inmap.talkingdata.com/#/docs/v2/tool