[R-sig-Geo] How to identify unknown Coordinate systems?

[MacQueen, Don]

I had data in an unknown projection -- but I knew exactly where it was
supposed to be located.

What I did was make a guess at its projection, transform it to lat/long,
export to KML, then open in Google Earth as an easy way to check whether
it was where it was supposed to be. Repeat until satisfied.

However, from other information I could limit the list of possible
projections, and that obviously helped.

-Don

-- 
Don MacQueen

Lawrence Livermore National Laboratory
7000 East Ave., L-627
Livermore, CA 94550
925-423-1062





On 7/24/12 9:36 AM, "Barry Rowlingson" <b.rowlingson at lancaster.ac.uk>
wrote:

>On Tue, Jul 24, 2012 at 5:17 PM, Juan Tomas Sayago
><juantomas.sayago at gmail.com> wrote:
>> Hello,
>> I have data in an unknown projection  but I know where more or less
>>where
>> it is located, but I don't know from what to transform to what I want to
>> use.
>
>First of all it could be one of the global systems like UTM zones.
>Find out which UTM zone you might expect it to be and see what the
>coordinates are of the region you think it might be.
>
>Also, make sure you haven't got a .prj file with your shapefile, or
>that the CRS is hidden in some metadata file.
>
>Or try looking up the geographical area here:
>
>http://www.spatialreference.org/
>
> but you might have to be creative - searching for 'Great Britain'
>doesnt find the British national grid system, but searching for
>'British' does. That site is also good for checking UTM zones. Note
>there's a lot of unofficial CRS in there.
>
> Another useful thing is to figure out if the coordinates are metres
>or km or miles, feet and inches - how far apart are your points in the
>coordinate system?
>
> If all that fails, if you have the location of some of your points in
>a known coordinate system, you can probably work out the transform
>yourself, but it's likely to be imprecise.
>
> Finally, try beating the person who gave you the data until they tell
>you! Or being nice to them.
>
>Barry
>
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