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From |
"Dimitriy V. Masterov" <dvmaster@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: calculating latitude and longitude of nearby point |

Date |
Thu, 9 Jun 2011 10:06:09 -0400 |

I think I may have figured out how to do this using plane geometry, which does not seem like a terrible approximation. My trig is a bit rusty, so I could not get the coordinates to come out using the formulas Scott referred to. Here's the code. I tried to verify the results using geodist. I am off by 1.6 meters. The two approaches do define the angles differently. ****************************************** clear; set obs 1; /* Find the lat/lon of a point one mile north of Stata HQ */ gen lat = 30.55233; gen lon = -96.24564; gen d = 1.609344; // 1 mile in km /* This method seems to work */ /* The constants 110540 and 111320 reflect the earth's oblateness (polar and equatorial circumferences are different). */ gen theta = _pi/2; // This formula measures angles counterclockwise from due east, so N = 90 deg or pi/2 in radians gen lat_new = lat + (d*sin(theta))/110540; gen lon_new = lon + (d*cos(theta))/(111320*cos(_pi*lat/180)); geodist lat lon lat_new lon_new, gen(distance); list; drop *_new distance theta; /* This does not work as implemented here, formulas from http://www.movable-type.co.uk/scripts/latlong.html */ gen theta = 0; // North is 0 deg/radians, and pi/2 or 90 deg is E in radians (different from above) gen lat_new = asin(sin(lat*_pi/180)*cos(d/6371) + cos(lat*_pi/180)*sin(d/6371)*cos(theta)); gen lon_new = lon + atan2(sin(theta)*sin(d/6371)*cos(_pi*lat/180),cos(d/6371)-sin(_pi*lat/180)*sin(_pi*lat_new/180)); geodist lat lon lat_new lon_new, gen(distance); list; ****************************************** * * 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: calculating latitude and longitude of nearby point***From:*Robert Picard <picard@netbox.com>

**References**:**st: calculating latitude and longitude of nearby point***From:*"Dimitriy V. Masterov" <dvmaster@gmail.com>

**Re: st: calculating latitude and longitude of nearby point***From:*Scott Merryman <scott.merryman@gmail.com>

**RE: st: calculating latitude and longitude of nearby point***From:*Nick Cox <n.j.cox@durham.ac.uk>

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