如何从vesselfinder（EPSG：4326到EPSG：3857）重新创建坐标转换？

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. Answers to this question are eligible for a +50 reputation bounty. ð᠍᠍ wants to to this question:

Hello foreigner, I just need to know what I am doing wrong. Please make sure, that the solution will contain code being able to produce the correct bboxes for vesselfinder from a given set of lat/lng, as seen in my question.

Many thanks!

I'm currently trying to figure out how vesselfinder.com calculates its Box Boundaries (bbox) which they use to query data from their backend.

Given an input like: lat, lon = 59.8230, 22.9586

They fetch data by using this bbox: 13761899,35886447,13779795,35898097

If I try to get a similar bbox by using bboxfinder.com , I get the following values, which aren't even close to what I was expecting: 2553560.4710,8358928.9331,2556565.4293,8360514.8411

The website above is using EPSG:4326 (WGS 84) to EPSG:3857 (WHS 84 / Pseudo-Mercator) by default. I tried to verify in the JS code of vesselfinder that they're using this conversion as well.

    var c = new s.geom.MultiLineString(t);
    return c.transform('EPSG:4326', 'EPSG:3857'),

There are also the following ones mentioned, but I'm pretty sure, that it has to be the upper shown transformation.

it = [
  new $('EPSG:3857'),
  new $('EPSG:102100'),
  new $('EPSG:102113'),
  new $('EPSG:900913'),

The questions now are: What am I doing wrong? / Where do I think wrong?

I also tried using Python for the conversion and even tried out the other mentioned EPSG:XXXXXX types, but haven't got the desired result. I also changed the order of both EPSG types when creating the Transformer, but again, not the desired results.

from pyproj import Transformer

TRAN_4326_TO_3857 = Transformer.from_crs("EPSG:4326", "EPSG:3857", always_xy=True)

lat = 59.823002
lon = 22.958583
expansion = 2000

res = TRAN_4326_TO_3857.transform(lng, lat)
bbox = (round(res[0]-expansion), round(res[1]-expansion), round(res[0]+expansion), round(res[1]+expansion))

print(bbox)
# (2455738, 8260436, 2655738, 8460436)

This one is close to the one I got from bboxfinder, but is again not even close to the bbox vesselfinder is using.

Answer 1

https://gis.stackexchange.com/a/370496 seems to have the math.

convertCoordinates(lon, lat) {
    var x = (lon * 20037508.34) / 180;
    var y = Math.log(Math.tan(((90 + lat) * Math.PI) / 360)) /
                  (Math.PI / 180);
    y = (y * 20037508.34) / 180;
    return [x, y];
}

Or, in C# ( https://gis.stackexchange.com/a/325551 )

public static double[] latLonToMeters(double lat, double lon)
{
    //Debug.Log(Mathd.Tan((90d + lat) * Mathd.PI / 720));
    //Debug.Log(Mathd.Tan((90d + lat) * Mathd.PI / 360d));
    double[] meters = new double[2];
    meters[0] = lat * originShift / 180d;
    meters[1] = Mathd.Log(Mathd.Tan((90d+lon) * Mathd.PI / 360d)) /
                   (Mathd.PI / 180d);
    //meters[1] = Mathd.Log(5) / (Mathd.PI / 180d);
    meters[1] = meters[1] * originShift / 180d;
    return meters;
}

In any case, note the website those came from; that may be a better place to get the algorithm. (Then if you need help converting to your preferred language, come back here.)