Generate random points from a given point coordinates

[rouault eleonor]

Hi,

I have a database of coordinates (lat, lon) and I would like to randomly generate a set of new coordinates on a circle around the initial coordinates (and not within a circle). For each point (lat,lon) I want to generate 20 points (lat1;lon1), ... (lat20;lon20), etc. I have already succeeded in generating coordinates within a circle around the centroids, but those are at a distance that varies. I would like all the new coordinates to be at a given distance from the initial points that have the coordinates (lat,lon) in the following code:

use coordinates.dta

forvalues i = 1/20 {
local phi = 2*runiform()*_pi
local r = 0.1
gen lon`i' = `r'* cos(`phi') + lon
gen lat`i' = `r'* sin(`phi') + lat
}

Any help or tips would be much appreciated!

[Scott Merryman]

Your code does generate random points on a circle. To visualize:

clear
set obs 200
gen lon = .
gen lat = .
qui  {
forvalues i = 1/200 {
local phi = 2*runiform()*_pi
local r = 0.1
replace lon = `r'* cos(`phi')  in `i'
replace lat = `r'* sin(`phi') in `i'
}
}
scatter lat lon, aspect(1)

[rouault eleonor]

Thank you very much !!