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Re: st: Gen Randomized geo coordinates within a range


From   Maarten Buis <maartenlbuis@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Gen Randomized geo coordinates within a range
Date   Fri, 19 Aug 2011 13:52:43 +0200

On Fri, Aug 19, 2011 at 12:36 PM, Maarten Buis <maartenlbuis@gmail.com> wrote:
> On Fri, Aug 19, 2011 at 11:17 AM,  <graupel75@gmail.com> wrote:
>> I need to generate a set of random geographic coordinates (x,y) given
>> a central point, within a given range.
>
> Alternatively, if you want your range to be a circle with radius .5
> you can do so as below
<snip>

In the previous example the three draws had the same relative position
with respect to their centroid, below you will get not only different
centroids but also different relative positions.

*-------------- begin example --------------
clear
input x y
1 1
5 5
1 5
end

gen phi = .
gen r = .
forvalues i = 1/30 {
	qui replace phi = 2*runiform()*_pi
	qui replace r = .5*runiform()
	gen xran`i' = r*cos(phi) + x
	gen yran`i' = r*sin(phi) + y
	local gr `"`gr' || scatter yran`i' xran`i'"'
}
scatter y x, aspect(1) `gr'
*-------------- end example -----------------
(For more on examples I sent to the Statalist see:
http://www.maartenbuis.nl/example_faq )

Hope this helps,
Maarten

--------------------------
Maarten L. Buis
Institut fuer Soziologie
Universitaet Tuebingen
Wilhelmstrasse 36
72074 Tuebingen
Germany


http://www.maartenbuis.nl
--------------------------

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