Php - getting the distance between multiple points using lon, lat and alt - php

Question

So i want to load a gpx file and get all the cordinates and calculate the total distance traveled, but im stuck with this code:
<?php
$xml = simplexml_load_file("data/example.gpx");
echo $xml->metadata->author->name;
echo "</br>";
echo "</br>";
echo "</br>";
$lon1=0;
$lat1=0;
$lon2=0;
$lat2=0;
$alt1=0;
$alt2=0;
$dist=0;
$brr = count($xml->trk->trkseg);
$brf = 0;
for($i = 0; $i<$brr; $i++){
$br = count($xml->trk->trkseg[$i]->trkpt);
$brf= $brf + $br;
for($j = 0; $j<$br;$j++){
$lat2= (float) $xml->trk->trkseg[$i]->trkpt[$j]['lat'];
$lon2= (float) $xml->trk->trkseg[$i]->trkpt[$j]['lon'];
$alt2= (float) $xml->trk->trkseg[$i]->trkpt[$j]->ele;
$lon2 = $alt2 * cos($lat2) * sin($lon2);
$lat2 = $alt2 * sin($lat2);
$alt2 = $alt2 * cos($lat2) * cos($lon2);
if ($j==0){ //this is just for the first time because first points are not set
$lat1=$lat2;
$lon1=$lon2;
$alt1= $alt2;
}
$cdist = sqrt(pow(($lat2-$lat1),2) + pow(($lon2-$lon1),2) + pow(($alt2-$alt1),2));
$dist = $dist + $cdist;
$lat1=$lat2;
$lon1=$lon2;
$alt1=$alt2;
}
}
echo 'Distance = '.$dist;
echo '</br>';
echo 'number of coordinates = '.$brf;
?>
as result for distance i get the number 4592.6244157763 instead of 4.10km (~~4100), but coordinates are good, it goes through all coordinates. (also, the gpx file is from endomondo if it matters)

Answer 1

Fixed the code, in case anyone needs it, here it is:
<?php
$xml = simplexml_load_file("data/vladantd.gpx");
echo $xml->metadata->author->name;
echo "</br>";
echo "</br>";
echo "</br>";
$lon1=0;
$lat1=0;
$lon2=0;
$lat2=0;
$alt1=0;
$alt2=0;
$dist=0;
$brr = count($xml->trk->trkseg);
$brf = 0;
for($i = 0; $i<$brr; $i++){
$br = count($xml->trk->trkseg[$i]->trkpt);
$brf= $brf + $br;
for($j = 0; $j<$br;$j++){
if($j==0)
{
$j=1;
$g=1;
}
$lat2= (float) $xml->trk->trkseg[$i]->trkpt[$j]['lat'];
$lon2= (float) $xml->trk->trkseg[$i]->trkpt[$j]['lon'];
$alt2= (float) $xml->trk->trkseg[$i]->trkpt[$j]->ele;
$lon2 = $alt2 * cos($lat2) * sin($lon2);
$lat2 = $alt2 * sin($lat2);
$alt2 = $alt2 * cos($lat2) * cos($lon2);
if ($g==1){
$lat1=$lat2;
$lon1=$lon2;
$alt1= $alt2;
$j=0;
$g=0;
}
$cdist = sqrt(pow(($lat2-$lat1),2) + pow(($lon2-$lon1),2) + pow(($alt2-$alt1),2));
$dist = $dist + $cdist;
$lat1=$lat2;
$lon1=$lon2;
$alt1=$alt2;
}
}
echo 'Distance = '.$dist;
echo '</br>';
echo 'number of coordinates = '.$brf;
?>
okay, so the files that i use, every first trkpt in every trkseg doesnt have an altitude, so if j==0 then set j to 1, so it skips that first point (it sets points 1 time every few seconds so it shouldnt make a big difference (in my case) and at the same time i've set another variable g to 1, so that we can at the end of this current loop, return j back to 0 so the j++ increases it to 1 instead of skipping the point and increasing it to 2, rest should be clear, if you have any questions, just ask ^^
EDIT:
The code isnt working good. The longer the distance, the bigger the mistake it makes, for 8.1km it shows 9km, tested it out on a few gpx files and noticed. Sorry, if someone has a solution, would mean a lot!