Leaflet: How to display a Geojson file with AutoCAD data?

Question

I am tried to display geojson file (converted from AutoCAD file to geojson) as the Second layer (first layer maps OSM ).

But geojson content occupies entire maps, not in a specific location.

How can we change coordinates in geojson file or how to reduce the height and width of geojson(second layer)? Please find below the Sample geojson file...

    {
  "type": "FeatureCollection",
  "name": "entities",
  "crs": {
    "type": "name",
    "properties": {
      "name": "urn:ogc:def:crs:OGC:1.3:CRS84"
    }
  },
  "features": [
    {
      "type": "Feature",
      "properties": {
        "Layer": "entities",
        "SubClasses": "AcDbEntity:AcDbPolyline",
        "EntityHandle": "1FFF0038"
      },
      "geometry": {
        "type": "LineString",
        "coordinates": [
          [
            0,
            0
          ],
          [
            0,
            319.9694
          ],
          [
            361.2444,
            319.9694
          ],
          [
            361.2444,
            0
          ],
          [
            0,
            0
          ]
        ]
      }
    },
    {
      "type": "Feature",
      "properties": {
        "Layer": "entities",
        "SubClasses": "AcDbEntity:AcDbPolyline",
        "EntityHandle": "1FFF011D"
      },
      "geometry": {
        "type": "LineString",
        "coordinates": [
          [
            0,
            252.0448
          ],
          [
            0,
            319.9694
          ],
          [
            361.2444,
            319.9278
          ],
          [
            361.2444,
            142.5544
          ],
          [
            0,
            142.5544
          ],
          [
            0,
            197.4439
          ],
          [
            9.1842,
            197.4439
          ],
          [
            9.1842,
            151.7295
          ],
          [
            352.0603,
            151.7295
          ],
          [
            352.0603,
            310.7537
          ],
          [
            9.1842,
            310.7932
          ],
          [
            9.1842,
            252.0448
          ],
          [
            0,
            252.0448
          ]
        ]
      }
    }
  ]
}

Answer 1

TL;DR: You're confusing the coordinate systems.

---

Coordinates in GeoJSON data refer to degrees of longitude in the X axis, and degrees of longitude in the Y axis. This is by definition . When these coordinates are mapped onto a cartesian plane, that becomes an equirectangular projection .

By contrast, coordinates in AutoCAD (or pretty much any other CAD software) usually refer to meters (or imperial feet) when there's an architect between the chair and the keyboard; also they usually refer to millimeters/centimeters (or tenths of an imperial inch) when there's a mechanical engineer between chair and keyboard.

So a line from -53, -10 to 0, 40 can be either a flight from Brazil to Spain, a 72-meter-long wall, or a 72mm length of cable.

Since you are using GeoJSON, and GeoJSON only cares about geographical coordinates in degrees of latitude/longitude, any software will assume that your coordinates are degrees of lat/long, and display them accordingly. The default for Leaflet is to project the data onto Web Mercator , and clip anything above/below +90/-90 degrees of latitude. This is to be expected.

---

So, the coordinate systems are wrong, what to do now? I see two approaches:

1. Change the CAD coordinates so they refer to lat-lng. This process is known as georeferencing . The specifics differ and can be complicated, sosearching through GIS StackExchange might be a good start.

2. Tell Leaflet to display non-geographical coordinates. Read the Leaflet tutorial on the topic , and use the crs: L.CRS.Simple option when instantiating your map. That should make your data display (more) correctly, but remember that GeoJSON is not an appropriate data format for non-geographical data .

In any case, be aware of your coordinate system .

Answer 2

Finally i got solution by unprojecting CRS EPSG3857 then the same geojson file working fine in leaflet.Thanks..

By adding,

L.CRS.EPSG3857.unproject(point) // where point is coords.