Re: st: RE: reverse vincenty

[Scott Merryman <scott.merryman@gmail.com>]

Try this:


//vincenty 41.75499 -124.194   ? -124.194, hav(5)
local lon1 =  -124.194
local lat1 = 41.75499
local d = 5
local R = 3956.5438
local maxlon =`lon1' + (180/_pi)*asin(sin((`d'/`R')) / cos(_pi/180*`lat1'))
local maxlat = `lat1' + (180/_pi)*(`d'/`R')
local minlon =`lon1' - (180/_pi)*asin(sin((`d'/`R')) / cos(_pi/180*`lat1'))
local minlat = `lat1' - (180/_pi)*(`d'/`R')

disp "Longitude (`maxlon' , `minlon')"
disp "Latitude (`maxlat' , `minlat')"

vincenty 41.75499 -124.194  41.75499 `maxlon'
return list

vincenty 41.75499 -124.194   `maxlat' -124.194
vincenty 41.75499 -124.194  41.75499 `minlon'
vincenty 41.75499 -124.194   `minlat' -124.194


Scott


On Wed, Oct 6, 2010 at 5:41 AM, Nick Cox <n.j.cox@durham.ac.uk> wrote:
> H Wright is presumably asking about commands, not functions. There is no inbuilt function in Stata (or Mata) for this calculation. A user-written Mata function should be perfectly doable.
>
> Also, -vincenty- is a user-written command from SSC (Austin Nichols).
>
> But I don't know of any such code.
>
> Nick
> n.j.cox@durham.ac.uk
>
> H Wright
>
> I have been using the vincenty function to calculate
> distances between latitudes and longitudes.  I would now like to find
> points that are X miles from a given coordinate.
>
> Is anyone aware of a function that would calculate a latitude  of a new point if all other inputs are know?
>
> For example :
>
> vincenty 41.75499 -124.194   ? -124.194, hav(5)
>
> So I  want to know the latitude of the point 5 miles away on the same longitude?
>
> I looked at the code in the vincenty ado file and it is beyond my mathematical ability to calculate this number myself.
>

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