Your final formula can be written more concisely: $distance = acos(cos($a1)*cos($b1)*cos($a2)*cos($b2) + cos($a1)*sin($b1)*cos($a2)*sin($b2) + sin($a1)*sin($a2)) * $r;
cos($b1)*cos($b2)+sin($b1)*sin($b2) = cos($b2-$b1) so $distance = $r * acos(sin($a1)*sin($b2)+cos($a1)*cos($a2)*cos($b2- $b1)) reference: http://www.biostat.umn.edu/~sudiptob/ResearchPapers/Geodesics.pdf --- In videoblogging@yahoogroups.com, "LeanBackVids.com" <[EMAIL PROTECTED]> wrote: > Chris Nolan [http://chrisnolan.ca/] has help to light a fire under my > ass about this outstanding math equation. Are there an math/geo gurus > out there who can help me to get this working? > > Here is a sample PHP page that attempts to display the distance > between Seattle and New York (given only their lat/lon values). > According to this, I'm getting 3869 miles between the two cities, but > my road atlas says only 2816 miles. > > // GET VARIABLES > $unit = $_REQUEST['unit']; > > // EARTH RADIUS > $radius_mi = 3443.9; > $radius_km = 6378; > > // VALUE OF PI > $pi = 3.14159265; > > // UNITS OF MEASUREMENT > if ($unit = "km") { > $r = $radius_km; > } else { > $r = $radius_mi; > } > > // SEATTLE LAT&LON > $a1 = 47.6125; > $b1 = -122.328; > > // NEW YORK LAT&LON > $a2 = 40.714; > $b2 = -74.007; > > // COMMENTS STOP HERE > // BECAUSE I'M LOST > > $a1 = abs($a1) * ($pi/180); > $b1 = abs($b1) * ($pi/180); > > $a2 = abs($a2) * ($pi/180); > $b2 = abs($b2) * ($pi/180); > > $distance = acos(cos($a1)*cos($b1)*cos($a2)*cos($b2) + > cos($a1)*sin($b1)*cos($a2)*sin($b2) + sin($a1)*sin($a2)) * $r; > > echo $distance . "<br />\n"; ------------------------ Yahoo! Groups Sponsor --------------------~--> Most low income households are not online. Help bridge the digital divide today! http://us.click.yahoo.com/cd_AJB/QnQLAA/TtwFAA/lBLqlB/TM --------------------------------------------------------------------~-> Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/videoblogging/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
