CiviCRM Community Forums (archive)

I have changed the calculation in civicrm/CRM/Contact/BAO/ProximityQuery.php to improve the accuracy. Below is the details of what I have done based on version 4.4

Original - line 244:
$where = "
{$tablePrefix}.geo_code_1  >= $minLatitude  AND
{$tablePrefix}.geo_code_1  <= $maxLatitude  AND
{$tablePrefix}.geo_code_2 >= $minLongitude AND
{$tablePrefix}.geo_code_2 <= $maxLongitude AND
$earthDistanceSQL  <= $distance
";

modification - line 244:  $where = "
{$tablePrefix}.geo_code_1  >= $minLatitude  AND
{$tablePrefix}.geo_code_1  <= $maxLatitude  AND
{$tablePrefix}.geo_code_2 >= $minLongitude AND
{$tablePrefix}.geo_code_2 <= $maxLongitude AND
acos(
      cos(radians( {$tablePrefix}.geo_code_1 ))
    * cos(radians( $latitude ))
    * cos(radians( {$tablePrefix}.geo_code_2 ) - radians( $longitude ))
    + sin(radians( {$tablePrefix}.geo_code_1 ))
    * sin(radians( $latitude ))
  )*6378137  <= $distance
";

I have tested the results against http://www.movable-type.co.uk/scripts/latlong.html . The difference are within 2%

Hope this would be helpful for whoever are having the similar issues with proximity Search

Hi Lobo,

Thanks for doing the patch!

The equation is the Great-circle distance, here is the wiki page http://en.wikipedia.org/wiki/Great-circle_distance

The change I made was based on it's Excel verion:   Distance = ACOS(SIN(lat1)*SIN(lat2)+COS(lat1)*COS(lat2)*COS(lon2-lon1))*6371
I found this at http://www.movable-type.co.uk/scripts/latlong.html

The only difference between my code and the excel code above is the radius of earth. I put 6378137m while the code above uses 6371km. I'm not too sure which one of them is more accurate.

Cheers,
George