array looping error

[unistake]

Hi all,

 

I am trying to calculate the straight line distance between two points by using their co-ordinates on each row from a mysql db that satisfies the query.

 

It works fine, except the last for loop below calculates $lat[$x+1],$long[$x+1] to have blank fields as they no longer exist in the database therefore i have invalid distances calculated.

 

My goal of this script is to find all the routes a particular day a flight attendant is working, by searching my db, rosters,  then gathering the departure and arrival airport from this table.

 

With these airports, I then extract their co-ordinates from the table, airports, and use the function below to calculate the distance.

 

Hope it makes sense what I am trying to do below!!

<?php
function distance($lat1, $lon1, $lat2, $lon2, $unit) {

  $theta = $lon1 - $lon2;
  $dist = sin(deg2rad($lat1)) * sin(deg2rad($lat2)) +  cos(deg2rad($lat1)) * cos(deg2rad($lat2)) * cos(deg2rad($theta));
  $dist = acos($dist);
  $dist = rad2deg($dist);
  $miles = $dist * 60 * 1.1515;
  $unit = strtoupper($unit);

  if ($unit == "K") {
    return ($miles * 1.609344);
  } else if ($unit == "N") {
      return ($miles * 0.8684);
    } else {
        return $miles;
      }
}



$today = '2016-01-04';
$sql = "SELECT * FROM rosters WHERE Code = 'TESTUSER' AND SectorDate = '$today' ORDER BY BeginTime ASC";
$result = mysqli_query($cxn,$sql)
	or die ("Cant get rosters distance.");

	$dep = array();
	$arr = array();
	$lat = array();
	$long = array();

	while($row=mysqli_fetch_array($result)) {
		$dep[] = $row['Dep'];	
		$arr[] = $row['Arr'];	
	}
	echo 'Number of flights: '.count($dep).'<br />';

	foreach($dep as $key => $value) {
		$sql = "SELECT * FROM airports WHERE IATA = '$value'";
		$result = mysqli_query($cxn,$sql)
			or die ("Cant get airport coordinates.");
		

		while($row=mysqli_fetch_array($result)) {
			$lat[] = $row['Latitude'];
			$long[] = $row['Longitude'];
		}
	}
	$max = count($dep);
		for ($x = 0; $x <= $max; $x++) {
			echo $dep[$x].' - '.$arr[$x].'<br />';
			echo floor(distance($lat[$x],$long[$x],$lat[$x+1],$long[$x+1], "N")) . "nm<br />";
		}
?>

[mac_gyver]

$x <= $max;

 

 

the problem is the above comparison in your for(){} loop.

 

$max is the count of the items in the array. if there are 10 items in the array, $max will be 10, but the array indexes would be 0-9. you would want to use $x < $max;

 

next, don't run queries inside of loops. this a performance killer. edit: run one JOINed query that gets the related data all at once. i would get a unique list of all the departure and arrival airports. then implode these into a comma separated list of quoted-string values, then use WHERE IATA IN(the list would go here) in ONE query to get all the lat/long values in one query.

 

 

edit: also, if i read what you are doing correctly, you would need to get the lat/long for the final arrival airport. your current code is only getting the lat/long for the departure airports. see the related edit i also made in the above paragraph.

Edited January 4, 2016 by mac_gyver

[requinix]

First, the condition should have been $x because $dep[$max] is one too far since the array keys will be 0 through $max-1.

What he said.

 

The problem is the loop is going too far, right? So don't make it go that far.

 

for ($x = 0; $x and then output the final lat/long pair since the loop didn't reach it.