This piece of code converts NMEA/GPS Lat -Long to Decimal Degrees. Code comments are self explanatory. The code is not graceful, but it works.
function degree2decimal($deg_coord){
//reference http://www.directionsmag.com/site/latlong-converter
//GPS/NMEA fixes are in Degree Minutes.m format
//for Google maps we need to convert them to decimal degrees
//sample format of GPS 4533.35 is 45 degrees and 33.35 minutes
//formula is as follows//Degrees=Degrees
//.d = M.m/60//Decimal Degrees=Degrees+.d
$degree=(int)($deg_coord/100); //simple way
$minutes= $deg_coord-($degree*100);
$dotdegree=$minutes/60;
$decimal=$degree+$dotdegree;
$direction=substr($deg_coord,-1);
//South latitudes and West longitudes need to return a negative result
if (($direction=="S") or ($direction=="W"))
{
$decimal=$decimal*(-1);}
$decimal=number_format($decimal,4,'.',''); //truncate decimal to 4 places
return $decimal;
}