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From |
"Kieran McCaul" <Kieran.McCaul@uwa.edu.au> |

To |
<statalist@hsphsun2.harvard.edu> |

Subject |
RE: st: RE: exact command for distance ? |

Date |
Sun, 13 Sep 2009 06:49:10 +0800 |

... To quote GH Hardy: "I am reluctant to intrude in a discussion concerning matters of which I have no expert knowledge,..." But, it seems to me that for each farm, you could create a quick screen that would remove the polygon points that were unlikely to be close to the farm. If f_lat and f_long are the coordinates of the farm and the coordinates for each polygon point are p_lat and p_long, then gen fp_lat = f_lat - p_lat gen fp_long = f_long - p_long gen dist = sqrt(fp_lat^2 + fp_long^2) qui sum dist, detail keep if dist<`r(p5)' If all your farms and lakes are in the UK, you would need to add a constant to the longitudes before calculating the differences (modulo 180 or 360; I don't know how longitude is specified in the data). ______________________________________________ Kieran McCaul MPH PhD WA Centre for Health & Ageing (M573) University of Western Australia Level 6, Ainslie House 48 Murray St Perth 6000 Phone: (08) 9224-2701 Fax: (08) 9224 8009 email: Kieran.McCaul@uwa.edu.au http://myprofile.cos.com/mccaul http://www.researcherid.com/rid/B-8751-2008 ______________________________________________ If you live to be one hundred, you've got it made. Very few people die past that age - George Burns -----Original Message----- From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Laura Platchkov Sent: Sunday, 13 September 2009 12:59 AM To: statalist@hsphsun2.harvard.edu Subject: RE: st: RE: exact command for distance ? Well, Roy, do you have any idea of how long it will take if i have one dataset with 800 points (farms) and the other, with 200'000 (points of lakes lines) ???? Stata has been running the whole afternoon now, and I am wondering whether I shouldn't maybe reduce the number of observaitons of the second dataset... Or Is there an amendment in the command that I could do in order for STATA to compute only the distances from the farms to the nearest lakes, and not from the points of the lakes to the nearest farms...? Laura * * 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/ * * 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: RE: exact command for distance ?***From:*Roy Wada <roywada@hotmail.com>

**References**:**RE: st: RE: exact command for distance ?***From:*Laura Platchkov <LMP881@bham.ac.uk>

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