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Now I'm trying to convert unknown coordinate system to Google Maps (WGS84?). How can I identify what kind of projection am I dealing with? I'm inspecting www.travelinesoutheast.org.uk. Route response returns json with:

name:"Epsom, Epsom Railway Station (Stop N)"
coords:"-29903.75584,5319390.31291"

name:"Epsom, Epsom Race Course (W-bound)"
coords:"-28583.17541,5323006.72201"

link to route search result

Midavalo
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Gabrielius B.
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  • Are you dealing with a shapefile? – Shahzad Bacha Sep 01 '16 at 05:43
  • these are just projected coordinates with unit in meters... what are you actually trying to do? – Shahzad Bacha Sep 01 '16 at 05:49
  • Identifying an unknown coordinate system can be quite a chore, especially if the data is old (older than 1984 at least), where did the data come from? Does your source have some metadata associated with it? – Michael Stimson Sep 01 '16 at 05:49
  • There are some hints at http://gis.stackexchange.com/questions/7839/identifying-coordinate-system-of-shapefile-when-unknown – PolyGeo Sep 01 '16 at 05:57
  • I need to convert those coordinates to format acceptable by Google Maps (i.e. ~ 51.334050, -0.269224). In browser developer tools network section I can find json file with starting and ending point coordinates and path but I don't know how to convert them.

    Here's json: http://goo.gl/UrqTHI

     – Gabrielius B. Sep 01 '16 at 06:18

1 Answers1

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The Eastings in the geojson are Google mercator coordinates (EPSG:3857), but Northing is calculated froma virtual axis 12000000m North of the equator, positive southwards.

You could use a custom CRS like this:

+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=-12000000 +k=1.0 +units=m +nadgrids=@null +wktext +axis=esu +no_defs

But unfortunately, the special Google Mercator conversion does not work that way.

So you have to calculate new northing from 12000000 - old Northing, then do the standard Google Mercator reprojection from 3857 to 4326.

The result looks like this, on an OpenStreetMap background:

enter image description here

AndreJ
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