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Can anyone identify what the following coordinate reference systems are?

This should be in Chester, UK: enter image description here

This should be in Eastbourne, UK: enter image description here

This should be in Horsham: enter image description here

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  • OSGB36 en.wikipedia.org/wiki/Ordnance_Survey_National_Grid
    – Mapperz
    Mar 12, 2020 at 15:01
  • to Convert them nearby.org.uk/coord-entry.html
    – Mapperz
    Mar 12, 2020 at 15:03
  • the numbers should be positive (-195514 northing might be a typo?)
    – Mapperz
    Mar 12, 2020 at 15:06
  • But OSGB36 usually is 6 and 6 numbers, these are 7 and 5 and 7 and 7, they don't map correctly. Could they be any other system as I have many in the same format. Mar 12, 2020 at 16:53
  • I guessed 3857 (web Mercator) or maybe a UTM zone like 32631 with values given in northing, easting order. Neither of those work. projfinder.com didn't really find anything useful.
    – mkennedy
    Mar 12, 2020 at 19:45

1 Answer 1

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The first thing that I noticed is that your coordinates seem quite inconsistent, suggesting that your points use a variety of different coordinate systems. That said, I managed to find out close matches for the points you mentioned:

The first 2 points look like they could be the x,y coordinates of the 3D geocentric coordinate system.

Using this coordinate system, when I display the points on a map, assuming an ellipsoidal height of 0, they fall within the specified cities:

Point 1 [3823572, -195514] (Chester): 53°12'12.6"N 2°55'37.9"W enter image description here

Point 2 [4042408, 19422.38] (Eastbourne): 50°45'48.1"N 0°16'31.0"E enter image description here

And the 3rd point fits EPSG:3035 (Lambert Azimuthal Equal Area Europe) which has the following proj string:

+proj=laea +lat_0=52 +lon_0=10 +x_0=4321000 +y_0=3210000 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs

With this coordinate system the point [3601400, 3157601] falls in Horsham at 51°04'19.3"N 0°18'22.2"W :

enter image description here

I don't know if your other points use one of those systems, but I would exert caution when interpreting and converting your coordinates. Ideally, all the points of a dataset should be in the same coordinate system, but it is not the case here.

Here are the formulas to calculate the geocentric z value and the latitude and longitude directly, assuming the points are in the Northern Hemisphere, and an ellipsoidal height of 0:

enter image description here

Where "a" is the equatorial radius (6,378,137 meters in WGS84) and "b" is the polar radius (6,356,752.3142 meters in WGS84)

Then, the latitude ϕ and the longitude λ can be computed this way:

enter image description here

λ = atan2(y, x)

Where

enter image description here

The accuracy of the results depends on how the points/coordinates were collected. If they indeed come from the 3D geocentric system, and the z value is missing, then there is no way of knowing the exact latitude of the point with only the x and y values, as it depends on the z value too. These simplified formulas only work when we consider the height to be 0. It should at least get you in the ballpark.

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  • Could you please provide the EPSG for the 3D geocentric system? Mar 13, 2020 at 15:39
  • 1
    It's EPSG 4978 for the WGS84 datum. Ideally you need the Z coordinate too, if you want to transform it, as this system is a 3D one. The Z in this system is not the altitude, but the distance between the equatorial plane and your point. So if you don't have a Z value, then you need to make some assumptions and compute it yourself. Tell me if you need the formulas, I can update my answer and provide them to you.
    – FSimardGIS
    Mar 13, 2020 at 21:48
  • great, yes if you could provide the formulas that would really help thanks Mar 14, 2020 at 0:45

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