javascript - 了解从 lon., lat. 的无证转换。地球表面坐标到图像的 x, y 坐标

问题描述

我尝试在从天气提供商收到的天气雷达图像上实现一些功能。在提供者网站上，我发现了一个函数，可以将用户输入的坐标转换为图像中的像素坐标。因为所有变量都是匿名的并且代码没有记录，所以我无法弄清楚该函数是如何工作的。我对坐标参考系统知之甚少，并且地图图像的 CRS 是未知的，因此我需要建议。

在下面的代码中，您可以看到我的代码分析进度。我花了将近一天的时间试图弄清楚 un25 代表什么变量。不成功。我不能盲目地将整个功能粘贴到我的项目中我需要了解背后的理论。

function lonlat2xy(lonUsrD, latUsrD) { //user input position in lon a lat in degrees
    var oneRadOfDegree = 57.29577951308232; //  for conversion of degrees to rads
    var latPragR = 50.008 / oneRadOfDegree; //lat. of base station, default position in rads
    var lonPragR = 14.447 / oneRadOfDegree; //lon. of base station, default position in rads
    var leftPragPx = 301.5;                 // length from left side of image to base station in px
    var topPragPx = 217.5;                  // length from top side of image to base station in px
    var ratioMap = 1.0;                     //ratio of the map (always 1 for thos example)
    var radiusEarth = 6378.144;         //radius of Earth
    var pi1 = 3.141592653589793;    //pi
    var pi2 = 6.283185307179586;    //2pi
    var pi05 = 1.570796326794897;   //0.5pi
    var lonUsrRNeg = -1 * (lonUsrD / oneRadOfDegree); //inversed user lon. position in rads
    var latUsrR = latUsrD / oneRadOfDegree;              //user lat. position in rads
    var lonPragRNeg = -1 * lonPragR;                     //inversed base station lon. position in rads
    var latPragR1 = latPragR;                            //base station lat. position in rads

    //?????? No idea what this formula does
    var un25 = (Math[sin](latUsrR) * Math[sin](latPragR1)) + (Math[cos](latUsrR) * Math[cos](latPragR1) * Math[cos](lonUsrRNeg - lonPragRNeg));
    sin()
    //??????

    var un26 = Math[acos](un25);

    un25 = Math[sin](latUsrR) - (Math[sin](latPragR1) * un25);
    var un27 = (Math[cos](latPragR1) * Math[sin](un26));


    if (un27 != 0) {
        un25 = un25 / un27;
    } else {
        un25 = 0;
    }

    var un28 = Math[acos](un25); 
    var lonDiffPragUsr = lonUsrRNeg - lonPragRNeg;
    if ((lonUsrRNeg > lonPragRNeg) && (lonDiffPragUsr < pi1)) {
        un28 = pi2 - un28; 
    }

    var un2a = un26;
    var un2b = un28; 
    var xPxImg, yPxImg, un2e;
    if (un2a < pi05) {
        un2e = Math[tan](un2a);
        xPxImg = un2e * Math[sin](un2b); 
        yPxImg = un2e * Math[cos](un2b);
    } else {
        xPxImg = 0;
        yPxImg = 0;
    }
    //[xy]PxImg - wrong name - I dont know what exactly this var represent
    xPxImg = leftPragPx + (xPxImg * radiusEarth) / ratioMap; //IMG-x = (IMGx prazske stanice)  + ((2PI*(pixN/pix360)) * polomer zeme)/ 1 ... ratio
    yPxImg = topPragPx - ((yPxImg * radiusEarth) / ratioMap);


    //Clear part from here
    var xPxImgRo = Math[round](xPxImg); //Round IMG-x
    var yPxImgRo = Math[round](yPxImg); //Round IMG-y

    out_xy = new Array(2);  //create array for rturn
    out_xy[0] = xPxImgRo;
    out_xy[1] = yPxImgRo;

    return out_xy; 
}

网址

供应商应用程序：http: //portal.chmi.cz/files/portal/docs/meteo/rad/data_jsradview.html

坐标转换图片示例：http: //portal.chmi.cz/files/portal/docs/meteo/rad/data_tr_png_1km/pacz23.z_max3d.20190824.1100.0.png

标签： javascriptcoordinatesgiscoordinate-systems

javascript - 了解从 lon., lat. 的无证转换。地球表面坐标到图像的 x, y 坐标

问题描述

解决方案

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