Question

I have a heat map which I use to visualize large scale GPS data with XAMPP-PHP-PostgreSQL back-end.

However, trying to visualize the GPS data of a big time interval – such as 24 hour data of 14 months – 2.4 million rows of latitude and longitude values, that is – causes my html page to crash.

I can visualize about 900.000 rows worth of data but I always get a crash for data bigger than that.

I used ini_set('memory_limit', '-1') and set_time_limit (60) to bypass the time limit and memory warnings by PHP but now I run into this Chrome browser crash problem.

What could be causing this? My PHP code that retrieves the latitude and longitude values are as following:

function getPoints($dateTimeBeg,$dateTimeEnd) //getting the points 
//from the database after providing the start and end date objects
{

    global $con, $coords, $coords_array; //$coords and $coords_array are declared
//at the beginning of the php script

    $query = "SELECT lat, lon FROM mytable WHERE calltime >= '$dateTimeBeg'
    and calltime <= '$dateTimeEnd'"; 

    $res = pg_query($con, $query) or die (pg_last_error($con)); 

    if($res)//if a result exists
    {
        $num_of_rows = pg_num_rows($res);

        if($num_of_rows > 0)
        {
            while($row = pg_fetch_row($res)) //fetch results row by row
            { 
                array_push($coords,array($row[0],$row[1]));      
//push them to the $coords array
            }
            array_push($coords_array,$coords); 
            unset($coords);
//push array $coords array to $coords_array ARRAY
        }
    }
}

$coords_json = json_encode($coords_array); //encode the results as json 
echo $coords_json; //print out the data, heatmap takes the 
//coordinates and takes care of the rest
unset($coords);
pg_close($con);

Answer 1

Looks like you’re returning 900,000+ data points back to the browser via json and asking the browser to handle the mapping… You might not have a php problem, but a browser overload problem.

You might try only sending every other result to the browser to see if that finishes (select all from db but only return half via json)… This could tell you if the problem is with the php or browser/JavaScript