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I know that is asked quite often but I'm still doing it again :)

I have a formula which I am not quite sure of the accuracy,

Northing : (Latitude - Base_Latitude) * ( 6378137 * pi/180 )

Easting : (Longitude - Base_Longitude) *(6378137 * pi/180) * cos(Base_Latitude * pi/180)

How accurate is this convertion? Is there a alternative/better one?

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    You say this has been asked before but you have not included any links to those Q&As. – PolyGeo Dec 2 '15 at 8:42
  • Then let's say similar questions. I'd like to have a answer on my question and not post links to other questions or answers ;) – Sanny Dec 2 '15 at 9:10
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    When asking questions here you are expected to include some of your prior research so that our volunteers do not just retrace your steps. – PolyGeo Dec 2 '15 at 9:13
  • OK did it. I have looked through the similar questions in the forum but can't find something close enough to my question. I am making position measurements (Lat/Long) and would like to convert them into x and y (east/north) so I can work with linear algebra. Because of that I was wondering how accurate the formula above is and if there is a better on. – Sanny Dec 2 '15 at 11:04
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    You would also need to multiply the (lon-base_lon) by 6378137*PI/180. It's the "equirectangular" projection. Not really good for much. If you're working in a very local area...eh. – mkennedy Dec 2 '15 at 17:49
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What you are looking for is a cartographic projection, the choice of which is a study area on its own; the accuracy of the projection depends on the area you are mapping and the type of distortion you are willing to afford (distance distortion in a particular distortion, area distortion, shape distortion).

There are about two hundred different projections, most of which have a lot of local variants. Try googling first. If you want better advice, you will have to provide us with more information about your data.

What you are using in the example is the Equirectangular projection, which is simple but only finds use in global thematic maps that do not require particular accuracy such as thematic maps.

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