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I have been given output in (what I believe to be) ECI format (from OrbitTools):

TSINCE            X                Y                Z

   0.00     4733.08693007    5370.64476064       0.09227655
 360.00    -3928.94737512   -4784.93071195   -3602.13095174
 720.00     2078.23905091    2928.47218732    6181.06427083
1080.00      343.60889986    -292.76288815   -7150.74620799
1440.00    -2682.96778230   -2415.73481378    6170.18900818

and need to convert the x,y pairs to latitude/longitude (to plot on a map where the object is above).

I can't reason through the conversion.

Is there a document that a laymen could get through or formula that would take a given time/point and yield a terrestrial latitude and longitude?

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I just did a bit of research on the internet and came across this (http://celestrak.com/columns/v02n01/). It gives a good explanation of how to convert between the two co-ordinate systems.

It seems getting the latitude from ECI is straight forward.

$Z = R sin \phi$ where R is the height of the above the centre of the Earth and $\phi$ is the latitude. X and Y are a bit difficult to convert and you will need to work through the document I linked.

Hope this helps (and hope this is related to what you were looking for)

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