如何在 javascript google map API 上显示带有米的 geojson 数据

Question

GeoJson file coordinates are in [X, Y] meters not in [lng, lat]. How to display it on google map?

GeoJson data

{
  "type": "FeatureCollection",
  "features": [
    {
      "type": "Feature",
      "geometry": {
        "type": "MultiPolygon",
        "coordinates": [
          [
            [
              [
                360590,
                555610
              ],
              [
                360590,
                555555.0128
              ],
              [
                360590,
                555540
              ],
              [
                360592.4439,
                555540
              ],
              [
                360600,
                555540
              ],
              [
                360600,
                555518.8277
              ]
            ]
          ]
        ]
      }
    }
  ]
}

here, [360590, 555610] - [X, Y] coordinates is in meters, Now we need to display this coordinates on google map, Is there any solution for this?

also we must have to use addGeoJson or loadGeoJson method because we have 200MB data in GeoJson file.

Answer 1

Converting in the backend would be better but there's a JS way too -- using proj4js and epsg.io to find the corresponding datums.

Important point: the first and last positions of the linear ring need to be identical. Otherwise your GeoJSON is not valid . So notice how my points array starts and ends w/ the same point.

---

After installing / importing proj4js :

// from https://epsg.io/27700
const EPSG_27700_DATUM = "+proj=tmerc +lat_0=49 +lon_0=-2 +k=0.9996012717 +x_0=400000 +y_0=-100000 +ellps=airy +towgs84=446.448,-125.157,542.06,0.15,0.247,0.842,-20.489 +units=m +no_defs";

// from https://epsg.io/4326
const WGS84_DATUM = "+proj=longlat +datum=WGS84 +no_defs";

const points = [[360590,555610],[360590,555555.0128],[360590,555540],[360592.4439,555540],[360600,555540],[360600,555518.8277],[360590,555610]];

const converted_points = points.map(([lon, lat]) => {
    return proj4(EPSG_27700_DATUM, WGS84_DATUM, [lon, lat]);
});

console.info({ converted_points });

Validating that your polygon is indeed inside of GB: