# Haversine formula with php

I want to use this formula with php. I have a database with some values of latitute and longitude saved.

I want to find, with a certain value of latitude and longitude in input, all the distances (in km) from this point with each point in the database. To do this, I used the formula on googlemaps api:

```( 6371 * acos( cos( radians(37) ) * cos( radians( lat ) ) * cos( radians( lng ) - radians(-122) ) + sin( radians(37) ) * sin( radians( lat ) ) ) )
```

Of course using that in php I replaced radians with deg2rad.The values 37,-122 are my values of input and lat,lng are my values in the database.

Below there is my code. The problem is that there is something wrong but I don't understand what. The value of distance is of course wrong.

```//values of latitude and longitute in input (Rome - eur, IT)
\$center_lat = "41.8350";
\$center_lng =  "12.470";

//connection to database. it works
(..)

//to take each value in the database:
\$query = "SELECT * FROM Dati";
\$result = mysql_query(\$query);
while (\$row = @mysql_fetch_assoc(\$result)){
\$lat=\$row['Lat']);
\$lng=\$row['Lng']);
}
```

For values for example: \$lat= 41.9133741000 \$lng= 12.5203944000

I have the output of distance="4826.9341106926"

The formula you used, seems to be the arccosine instead of the haversine formula. The haversine formula is indeed more appropriate to calculate the distance on a sphere, because it is not prone to rounding errors with antipodal points.

```/**
* Calculates the great-circle distance between two points, with
* the Haversine formula.
* @param float \$latitudeFrom Latitude of start point in [deg decimal]
* @param float \$longitudeFrom Longitude of start point in [deg decimal]
* @param float \$latitudeTo Latitude of target point in [deg decimal]
* @param float \$longitudeTo Longitude of target point in [deg decimal]
* @return float Distance between points in [m] (same as earthRadius)
*/
function haversineGreatCircleDistance(
\$latitudeFrom, \$longitudeFrom, \$latitudeTo, \$longitudeTo, \$earthRadius = 6371000)
{
// convert from degrees to radians

\$latDelta = \$latTo - \$latFrom;
\$lonDelta = \$lonTo - \$lonFrom;

\$angle = 2 * asin(sqrt(pow(sin(\$latDelta / 2), 2) +
cos(\$latFrom) * cos(\$latTo) * pow(sin(\$lonDelta / 2), 2)));
}
```

P.S. I couldn't find an error in your code, so is it just a typo that you wrote \$lat= 41.9133741000 \$lat= 12.5203944000 ? Maybe you just calculated with \$lat=12.5203944000 and \$long=0 because you overwrote your \$lat variable.

Edit:

Tested the code and it returned a correct result:

```\$center_lat = 41.8350;
\$center_lng = 12.470;
\$lat = 41.9133741000;
\$lng = 12.5203944000;

// test with your arccosine formula
print(\$distance); // prints 9.662174538188

// test with my haversine formula
\$distance = haversineGreatCircleDistance(\$center_lat, \$center_lng, \$lat, \$lng, 6371);
print(\$distance); // prints 9.6621745381693
```

```public function getDistanceBetweenTwoPoints(\$point1 , \$point2){
// array of lat-long i.e  \$point1 = [lat,long]
\$point1Lat = \$point1;
\$point2Lat =\$point2;
\$point1Long =\$point1;
\$point2Long =\$point2;
\$a = sin(\$deltaLat/2) * sin(\$deltaLat/2) + cos(deg2rad(\$point1Lat)) * cos(deg2rad(\$point2Lat)) * sin(\$deltaLong/2) * sin(\$deltaLong/2);
\$c = 2 * atan2(sqrt(\$a), sqrt(1-\$a));

return \$distance;    // in km
}
```

```function getDistance(\$latitude1, \$longitude1, \$latitude2, \$longitude2) {

\$a = sin(\$dLat/2) * sin(\$dLat/2) + cos(deg2rad(\$latitude1)) * cos(deg2rad(\$latitude2)) * sin(\$dLon/2) * sin(\$dLon/2);
\$c = 2 * asin(sqrt(\$a));

return \$d;
}
```

As you can see there are many differences between this as your code. I don't know if you have either a different approach to the formula or maybe some step when converting to PHP went wrong, but the above formula should work.

I calculate distances straight inside queries, using the following stored procedure:

```CREATE FUNCTION GEODIST (lat1 DOUBLE, lon1 DOUBLE, lat2 DOUBLE, lon2 DOUBLE)
RETURNS DOUBLE
DETERMINISTIC
BEGIN
DECLARE dist DOUBLE;
RETURN dist;
END|
```

You just execute the above as an SQl statement from within phpMyAdmin to create the procedure. Just notice the ending |, so in your SQL input window, choose for the | sign as limiter.

Then in a query, call it like this:

```\$sql = "
SELECT `locations`.`name`, GEODIST(`locations`.`lat`, `locations`.`lon`, " . \$lat_to_calculate . ", " . \$lon_to_calculate . ") AS `distance`
FROM `locations` ";
```

I found this to be a lot faster than calculating it in PHP after the query has been run.

I making the class of haversign which having the static fuction getDistance having the four paramters and it return the distance from the bot location points

```class HaverSign {

public static function getDistance(\$latitude1, \$longitude1, \$latitude2, \$longitude2) {

\$a = sin(\$dLat/2) * sin(\$dLat/2) + cos(deg2rad(\$latitude1)) * cos(deg2rad(\$latitude2)) * sin(\$dLon/2) * sin(\$dLon/2);
\$c = 2 * asin(sqrt(\$a));

return \$d;
}
}
```

above class is stored at the root directory and root directory contains classes folder Call this by using the following way in any php page

```include "../classes/HaverSign.php";
\$haversign=new HaverSign();

\$lat=18.5204;
\$lon=73.8567;

\$lat1=18.5404;
\$lon1=73.8167;

\$dist = \$haversign->getDistance(\$lat,\$lon,\$lat1,\$lon1);
echo \$dist;
```

Output is as follow

```4.7676529976827
```