# This function is for getting the distance between two points on the earths surface, and should not be used to calculate linear distances. To calculate linear distances use the function at https://QRdvark.com/examples/Get-Linear-Distance.php

In this example the co-ordinates are taken form the cities database located at https://QRdvark.com/examples/US-Cities-Zip-Codes.html. We have chosen Barcelona and High Springs, Florida for the example.

The function is called getRiemannDistance() in honour of Bernhard Riemann, who in the nineteenth centuary first formulated spherical and hyperbolic geometry. Thanks Bernhard, you're a rock.

``` <?php /**  *  * @get distance from latitude and longitute  *  * @param float \$lat_from  *  * @param float \$long_from  *  * @param float \$lat_to  *  * @param float *long_to  *  * @param \$unit options k, m, n, Default k  *  * @return float  *  */  function getRiemannDistance(\$lat_from, \$long_from, \$lat_to, \$long_to, \$unit='k'){  /*** distance unit ***/  switch (\$unit):  /*** miles ***/  case 'm':     \$unit = 3963;     break;  /*** nautical miles ***/  case 'n':     \$unit = 3444;     break;  default:     /*** kilometers ***/     \$unit = 6371;  endswitch;  /*** 1 degree = 0.017453292519943 radius ***/  \$degreeRadius = deg2rad(1);    /*** convert longitude and latitude to radians ***/  \$lat_from  *= \$degreeRadius;  \$long_from *= \$degreeRadius;  \$lat_to    *= \$degreeRadius;  \$long_to   *= \$degreeRadius;    /*** apply the Great Circle Distance Formula ***/  \$dist = sin(\$lat_from) * sin(\$lat_to) + cos(\$lat_from)  * cos(\$lat_to) * cos(\$long_from - \$long_to);    /*** radius of earth * arc cosine ***/  return (\$unit * acos(\$dist)); } /*** example usage ***/ /*** Barcelona ***/\$lat_from = 18.4525;\$long_from = -66.538889; /*** High Springs Florida ***/\$lat_to = 29.841022;\$long_to = -82.615628; /*** calculate the distance in miles ***/\$distance = getRiemannDistance(\$lat_from, \$long_from, \$lat_to, \$long_to, 'm'); /*** round it off and echo ***/echo round( \$distance ) . ' miles';?>```