David Torres<[email protected]> :
This is in reference to e.g.
http://stata.com/statalist/archive/2009-07/msg00083.html
http://stata.com/statalist/archive/2007-01/msg00098.html
I believe.
Note that standard Stata commands like -summarize- and -replace-
inside the loop do all the work of saving characteristics of the
nearest, or k nearest, observations (and whatever else, such as mean
of Z over those with distance less than 10 units). No program like
-vincenty- (on SSC) does that; a -replace- command does it.
-vincenty- does not return "the min, max, mean, or whatever" and it
appears that -globdist- (which I found with -findit-) does only part
of what -vincenty- does (and the -globdist- help file contains the
caveat that "Testing of this program has been limited"). In other
words, add a -replace- to put the result you want in a variable.
Maybe you want something like:
g long rad10=.
g double dist1=.
g id1=""
g xy1=""
merge using univpoints00_0
forv i=1/`np' {
qui vincenty `=latitude[`i']' `=longitude[`i']' sch_lat sch_lon, hav(dis)
g within10=dis<10
su within10, meanonly
qui replace rad10=r(sum) in `i'
su dis, meanonly
qui replace dist1=r(min) in `i'
qui levelsof unitid if dis==dist1[`i'], loc(vs)
foreach v of loc vs {
qui replace id1="`v' "+id1 in `i'
su sch_lat if unitid==`v', meanonly
loc y1=r(mean)
su sch_lon if unitid==`v', meanonly
loc x1=r(mean)
qui replace xy1="(`x1',`y1') "+id1 in `i'
}
drop dis within10
}
On Sat, Aug 29, 2009 at 4:26 PM, David Torres<[email protected]> wrote:
I am trying to calculate multiple distances from one set of xy coordinates
to another
using vincenty. In addition to getting those distances, however, I need to
somehow list
the ids for the xy coordinates used to calculate the distance.
Here is the piece of code I'm working with:
code excerpt:
g long rad10=.
g double dist1=.
g id1=""
merge using univpoints00_0
forv i=1/`np' {
qui vincenty `=latitude[`i']' `=longitude[`i']' sch_lat sch_lon, hav(dis)
g within10=dis<10
su within10, meanonly
qui replace rad10=r(sum) in `i'
su dis, meanonly
qui replace dist1=r(min) in `i'
qui levelsof unitid if dis==dist1[`i'], loc(vs)
foreach v of loc vs {
qui replace id1="`v' "+id1 in `i'
}
drop dis within10
}
end excerpt
As you can see, I'm getting a count of all sch_lat and sch_lon coordinates
within a 10
mile radius of the other set of latitude and longitude points. Then I
return only the
minimum distance. Will vincenty allow for returning more than just the min,
max, mean,
or whatever? Or is globdist a better choice for returning multiple
distances and the ids
attached to the point the distance to which is being calculated?
Thanks
David Torres
UMich
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