I want to show specific information depending on where i am.
I have five cities with different information, and i want to show that city(information) that i'm closest to.
How to i do that the simplest way, using javascript.
Ex.
If i store the cities lat, long in an array
var cities = [
['new york', '111111', '222222', 'blablabla']
['boston', '111111', '222222', 'blablabla']
['seattle', '111111', '222222', 'blablabla']
['london', '111111', '222222', 'blablabla']
]
And with my current location(lat, long) i want the city that i'm closet to.
On your computer, open Google Maps. Right-click the place or area on the map. This will open a pop-up window. You can find your latitude and longitude in decimal format at the top.
Open 'Google Maps': Open maps.google.com in your browser. Click on the search bar: Now click on the search bar at the top left corner. Enter the latitude and coordinates: Now enter the latitude and longitude in Google maps.
Reverse geocoding is the process to convert the latitude and longitude coordinates to a readable address. Type the lat long coordinates and press Convert button. Reverse geocoded address will shown below. Also the municipality, subdivision and country name can be found.
Here is a basic code example using HTML5 geolocation to get the user's position. It then calls NearestCity()
and calculates the distance (km) from the location to each city. I passed on using the Haversine formulae and instead used the simpler Pythagoras formulae and an equirectangular projection to adjust for the curvature in longitude lines.
// Get User's Coordinate from their Browser
window.onload = function() {
// HTML5/W3C Geolocation
if (navigator.geolocation) {
navigator.geolocation.getCurrentPosition(UserLocation);
}
// Default to Washington, DC
else
NearestCity(38.8951, -77.0367);
}
// Callback function for asynchronous call to HTML5 geolocation
function UserLocation(position) {
NearestCity(position.coords.latitude, position.coords.longitude);
}
// Convert Degress to Radians
function Deg2Rad(deg) {
return deg * Math.PI / 180;
}
function PythagorasEquirectangular(lat1, lon1, lat2, lon2) {
lat1 = Deg2Rad(lat1);
lat2 = Deg2Rad(lat2);
lon1 = Deg2Rad(lon1);
lon2 = Deg2Rad(lon2);
var R = 6371; // km
var x = (lon2 - lon1) * Math.cos((lat1 + lat2) / 2);
var y = (lat2 - lat1);
var d = Math.sqrt(x * x + y * y) * R;
return d;
}
var lat = 20; // user's latitude
var lon = 40; // user's longitude
var cities = [
["city1", 10, 50, "blah"],
["city2", 40, 60, "blah"],
["city3", 25, 10, "blah"],
["city4", 5, 80, "blah"]
];
function NearestCity(latitude, longitude) {
var minDif = 99999;
var closest;
for (index = 0; index < cities.length; ++index) {
var dif = PythagorasEquirectangular(latitude, longitude, cities[index][1], cities[index][2]);
if (dif < minDif) {
closest = index;
minDif = dif;
}
}
// echo the nearest city
alert(cities[closest]);
}
With HTML5, you can pull the location of the user and then compares this example using a Haversine function (function below taken from here):
function getDistanceFromLatLonInKm(lat1,lon1,lat2,lon2) {
var R = 6371; // Radius of the earth in km
var dLat = deg2rad(lat2-lat1); // deg2rad below
var dLon = deg2rad(lon2-lon1);
var a =
Math.sin(dLat/2) * Math.sin(dLat/2) +
Math.cos(deg2rad(lat1)) * Math.cos(deg2rad(lat2)) *
Math.sin(dLon/2) * Math.sin(dLon/2)
;
var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a));
var d = R * c; // Distance in km
return d;
}
function deg2rad(deg) {
return deg * (Math.PI/180)
}
You can calculate the distance by latitude with your location and the cities locations. And find the shortest and draw. To calculate you can read more in http://www.movable-type.co.uk/scripts/latlong.html
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