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From |
Austin Nichols <austinnichols@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: spatial analysis - DISTANCE |

Date |
Sun, 30 Aug 2009 05:30:13 -0400 |

David Torres<torresd@umich.edu> : 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<torresd@umich.edu> 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 * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**RE: st: spatial analysis - DISTANCE***From:*Roy Wada <roywada@hotmail.com>

**Re: st: spatial analysis - DISTANCE***From:*David Torres <torresd@umich.edu>

**Re: st: spatial analysis - DISTANCE***From:*David Torres <torresd@umich.edu>

**References**:**st: spatial analysis - DISTANCE***From:*David Torres <torresd@umich.edu>

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