as per the guide here https://www.intelliwolf.com/find-nearest-location-from-array-of-coordinates-php/
I am trying to write a version that finds the nearest "ID" from the JSON feed found at https://easytide.admiralty.co.uk/Home/GetStations
So far I have constructed the following sandbox https://3v4l.org/JX0i5#v7.3.1
<?PHP
// json will eventually be obtained via json_decode(file_get_contents('https://easytide.admiralty.co.uk/Home/GetStations')
$json = '
{
"type": "FeatureCollection",
"features": [{
"type": "Feature",
"geometry": {
"type": "Point",
"coordinates": [
-4.702540,
51.672791
]
},
"properties": {
"Id": "1603",
"Name": "TENBY",
"Country": "Channel Islands",
"ContinuousHeightsAvailable": true
}
}, {
"type": "Feature",
"geometry": {
"type": "Point",
"coordinates": [
-1.878530,
50.721680
]
},
"properties": {
"Id": "1603A",
"Name": "Bournmouth",
"Country": "Channel Islands",
"ContinuousHeightsAvailable": true
}
}, {
"type": "Feature",
"geometry": {
"type": "Point",
"coordinates": [
-2.35,
49.433333
]
},
"properties": {
"Id": "1603A",
"Name": "Maseline Pier",
"Country": "Channel Islands",
"ContinuousHeightsAvailable": true
}
}]
}';
$locations = json_decode($json, true);
#print_r($locations); //check json decoded
// set the base location will eventually be passed via $_GET
$base_location = array(
'lat' => "51.672791",
'lng' => "-4.702540"
);
//create the array for recording the calculated distances
$distances = array();
//sure this count is not needed but used it to check the array was being read
for ($c = 0; $c < count($locations["features"]); $c ) {
// this is where I go wrong
foreach($locations as $i){
foreach ($i as $z) {
foreach ($z['geometry'] as $key => $location) {
if ($key == "coordinates"){
# print_r($z);
//work out the distance Pythagorean Theorem calculating how far it is from $base_location is
$a = $base_location['lat'] - $location[1];
$b = $base_location['lng'] - $location[0];
$distance = sqrt(($a**2) ($b**2));
$distances[$c] = $distance;
//nonsense used to test I was getting the correct output
echo "The value of key '$key' is '$location'", PHP_EOL;
}
}
}
}
}
#print_r($base_location);
//sort distances to get the closest first
asort($distances);
print_r($distances);
//not really got to this part yet but want to return the "properties=>ID"
$closest = $location[key($distances)];
#print_r($closest);
#echo "<br>Closest port from ARRAY is: " . $closest['features'][1]['properties']['Id'];
I would love for someone to explain in simple terms how I get this to work:-
- search the array found at https://easytide.admiralty.co.uk/Home/GetStations
- find the nearest location based on the lat/long provided
- print the "properties=>ID" from the corresponding array (to be used later in another file_get_contents request)
I have poured over it for many hours and have posted other versions of this question which were automatically closed.
I want to create this as a learning project but am stuck on this element. If this is not the place to ask for this type of help, please advise where is.
Many thanks
CodePudding user response：
This seemed like an interesting exercise, a bit of a cast around and all the code you need is out there for you to utilise
function getDistance($from_lat, $from_long, $to_lat, $to_long, $unit = 'nmi', $decimals = 2) {
// Calculate the distance in degrees
$degrees = rad2deg(acos((sin(deg2rad($from_lat))*sin(deg2rad($to_lat))) (cos(deg2rad($from_lat))*cos(deg2rad($to_lat))*cos(deg2rad($from_long-$to_long)))));
// Convert the distance in degrees to the chosen unit (kilometres, miles or nautical miles)
switch($unit) {
case 'km':
$distance = $degrees * 111.13384; // 1 degree = 111.13384 km, based on the average diameter of the Earth (12,735 km)
break;
case 'mi':
$distance = $degrees * 69.05482; // 1 degree = 69.05482 miles, based on the average diameter of the Earth (7,913.1 miles)
break;
case 'nmi':
$distance = $degrees * 59.97662; // 1 degree = 59.97662 nautic miles, based on the average diameter of the Earth (6,876.3 nautical miles)
}
return round($distance, $decimals);
}
$json_stations = file_get_contents('https://easytide.admiralty.co.uk/Home/GetStations');
$stations = json_decode($json_stations);
#$i_am_here = ['lat' => 50.77842324616663, 'lng' => -1.087804949548603]; # Castle Field Portsmouth
$closest = []; // index into stations
$distance = null;
foreach ($stations->features as $index => $feature){
$lng = $feature->geometry->coordinates[0];
$lat = $feature->geometry->coordinates[1];
$dist = getDistance($i_am_here['lat'], $i_am_here['lng'], $lat, $lng, $unit = 'nmi', $decimals = 4);
if ( $distance == NULL || $dist < $distance ){
$distance = $dist;
$closest = ['distance' => $dist, 'index' => $index, 'properties' => $feature->properties];
}
}
print_r($closest);
echo 'Distance = ' . $distance;
RESULTS
Array
(
[distance] => 1.6947
[index] => 85
[properties] => stdClass Object
(
[Id] => 0065
[Name] => PORTSMOUTH
[Country] => England
[ContinuousHeightsAvailable] => 1
)
)
Distance = 1.6947
CodePudding user response：
I managed to work out a 'solution' but perhaps not the most graceful?
foreach($locations as $i){
if (is_array($i) || is_object($i)) {
foreach ($i as $z) {
foreach ($z['geometry'] as $key => $location) {
if ($key == "coordinates"){
# print_r($z);
$a = $base_location['lat'] - $location[1];
$b = $base_location['lng'] - $location[0];
$distance = sqrt(($a**2) ($b**2));
$distances[$c ] = $distance;
# echo "The value of key '$key' is '$location'", PHP_EOL;
}
}
}
}
}
asort($distances);
$closest = $i[key($distances)];
print_r($closest);
echo "Closest Id: " . $closest['properties']['Id']. " name: " . $closest['properties']['Name'];