[GIS] Add EPSG:3857 geometries to map using Leaflet

coordinate systemleaflet

Right now Leaflet can only add geometries with latitude and longitude values onto the map.

If we have a EPSG:3857 point, whose x=-11819829 and y=4200860, how can I add it onto the map?

If this point needs to be unprojected as geographical coordinates, how to implement it?

Best Answer

Are you sure you have the right projection in mind? According to SpatialReference.org, you're talking about Web Mercator which, as its name implies, has (decimal) degrees as linear units. EPSG 3857 is, in fact, the default projection used by Leaflet and most web mapping frameworks. As the underlying SRS is WGS84, you should be able to treat your EPSG 3857 coordinates as unprojected geographical coordinates (GCS WGS84).

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[GIS] Requesting map tiles from a wms server in epsg:900913 fails

Latitude and Longitude can be in many projections, however in the case of the iPhone (and any other mobile device for that matter) it is most likely WGS84 coming from the device's GPS and would therefore be EPSG:4326. EPSG:900913 and EPSG:3857 are both Web Spherical Mercator projections and are based on metres and not degrees.

Ordinarily you would need to transform the coordinates using something like Proj4. However, in your case the WMS you are targeting will support requests for data in EPSG:4326 so you will be able to make the request without having to transform your coordinates. This can be seen in the response to a GetCapabilities request to that server. The XML response provides all the details you need to know how to connect to the server and request data.

[GIS] Using UTM in leaflet efficiently

You can use the transform set up in proj4leaflet. I expect that you have already crated a CRS in your map.options.

var my_crs = map.options.crs; // get the CRS
var my_proj = my_crs.projection; // get the projection
// transform the lat lon Point to a utm point
var my_utm_point = my_proj.project(point_in_latlng);

If you want to set the internal coordinate system to UTM in leaflet I think you have to do a lot of recoding or use openLayers instead.

Best Answer

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