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 10-11-2012, 04:57 AM PM User | #1 sonny Regular Coder     Join Date: Apr 2008 Location: United States Posts: 567 Thanks: 88 Thanked 0 Times in 0 Posts Calculate distance by Lat-Lon Hi Can someone please check this, the miles do not seem right when I test it PHP Code: ```     function distance(\$lat1, \$lng1, \$lat2, \$lng2, \$miles = true){     \$pi80 = M_PI / 180;     \$lat1 *= \$pi80;     \$lng1 *= \$pi80;     \$lat2 *= \$pi80;     \$lng2 *= \$pi80;           \$r = 6372.797; // mean radius of Earth in km     \$dlat = \$lat2 - \$lat1;     \$dlng = \$lng2 - \$lng1;     \$a = sin(\$dlat / 2) * sin(\$dlat / 2) + cos(\$lat1) * cos(\$lat2) * sin(\$dlng / 2) * sin(\$dlng / 2);     \$c = 2 * atan2(sqrt(\$a), sqrt(1 - \$a));     \$km = \$r * \$c;           return (\$miles ? (\$km * 0.621371192) : \$km); } \$lat1 = "39.9289";//Beijing China \$lon1 = "116.3883"; \$lat2 = "47.6026";//Seattle Washington \$lon2 = "-122.3284"; \$distance = distance(\$lat1, \$lon1, \$lat2, \$lon2); echo "They are ".\$distance." miles away from each other  ``` Last edited by sonny; 10-11-2012 at 06:10 AM..