I'm having an issue with calculating distances.
I have installed postgis, and I'm saving Lng/Lat points in the database
CREATE TABLE geo (gid serial PRIMARY KEY, geo geography)
For inserting a record, this is what I do:
INSERT INTO geo (geo) VALUES (ST_MAKEPOINT(Lng,Lat)::geography))
When I do the following query with some Lng/Lat variables, I get the following output:
SELECT gid, ST_DISTANCE(geo, ST_MAKEPOINT(Lng2,Lat2)::geography) FROM geo;
----
OUTPUT: 1 424.02930940m
Secondly, when I do the exact same calculation with the following formula (haversine formula in javascript), I get a slightly different output.
/*
const coords1/2 = {
lat: // latitude,
lng: // longitude
};
*/
export const haversine = (coords1, coords2) => {
var R = 6371000;
var x1 = coords2.lat - coords1.lat;
var dLat = x1.toRad();
var x2 = coords2.lng - coords1.lng;
var dLon = x2.toRad();
var a = Math.sin(dLat / 2) * Math.sin(dLat / 2) +
Math.cos(coords1.lat.toRad()) * Math.cos(coords2.lat.toRad()) *
Math.sin(dLon / 2) * Math.sin(dLon / 2);
var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
var d = R * c;
return d;
};
----
OUTPUT: 422.20392010m
It's a difference of 2 meters, but I need the most accurate of the 2. It's for an app for geocaching.
I'm currently using the haversine formula in my app, but I'm thinking about switching to postgis because it would simplify my queries a lot.
Which one can I rely on the most?
Related
Is there a way to calculate the travelled distance in Mapbox?
For example: if a user clicks the start button it'll record the travelled path and calculate the distance. I know it's possible to calculate a distance between two geopoints described here, however a user can go off-road and therefore won't choose to walk the fastest/most suited route between two geopoints. I would like to sum ALL walked kilometers.
Monitor position
navigator.geolocation.watchPosition(function(position) {
document.getElementById('distance').innerHTML =
calculateDistance(startPos.coords.latitude, startPos.coords.longitude,
position.coords.latitude, position.coords.longitude);
});
Calculate distance
function calculateDistance(lat1, lon1, lat2, lon2) {
var R = 6371; // km
var dLat = (lat2 - lat1).toRad();
var dLon = (lon2 - lon1).toRad();
var a = Math.sin(dLat / 2) * Math.sin(dLat / 2) +
Math.cos(lat1.toRad()) * Math.cos(lat2.toRad()) *
Math.sin(dLon / 2) * Math.sin(dLon / 2);
var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
var d = R * c;
return d;
}
Number.prototype.toRad = function() {
return this * Math.PI / 180;
}
EDIT: one possible solution could be that every time I get a new location I calculate distance between previous geopoint and new geopoint and use that to calculate distance. If I want to see total distance I sum all the distances between previous points. I can also use that data to plot a line between all stored geopoints. Does this makes sense? Is there a more efficient way to do this since this is a pure javascript solution (maybe there is a more related to Mapbox solution?)
So I am using google.maps.geometry.spherical.computeDistanceBetween in Javascript and computeDistanceBetween from SphericalUtil in Java.
https://github.com/googlemaps/android-maps-utils/blob/master/library/src/com/google/maps/android/SphericalUtil.java
I am getting different distances for the same positions. Is there anything I can do to calibrate them to be the same or are there two libraries I can use that can get me similar results in the front end (Javascript) and back end (Java)?
Below are some values and an example:
In Javascript:
var from = new google.maps.LatLng(33.44138, -111.97500000000002);
var to = new google.maps.LatLng(33.505904166596224, -112.09470748901367);
var distanceBetween = google.maps.geometry.spherical.computeDistanceBetween(from, to);
console.log(distanceBetween);
In Java:
LatLng from = new LatLng(Float.parseFloat("33.44138"), Float.parseFloat("-111.97500000000002"));
LatLng to = new LatLng(Float.parseFloat("33.505904166596224"), Float.parseFloat("-112.09470748901367"));
double distanceBetween = SphericalUtil.computeDistanceBetween(from, to);
System.out.println(distanceBetween);
In Java with Double instead of Float:
LatLng from = new LatLng(Double.parseDouble("33.44138"), Double.parseDouble("-111.97500000000002"));
LatLng to = new LatLng(Double.parseDouble("33.505904166596224"), Double.parseDouble("-112.09470748901367"));
double distanceBetween = SphericalUtil.computeDistanceBetween(from, to);
System.out.println(distanceBetween);
The Javascript value is: 13234.355969270651
The Java (float) value is: 13219.474110913057
The Java (double) value is: 13219.565680296535
Thanks!
Check the documentation for the value of earth radius that is used.
Try using this code to compare results to the 2 others.
Tier3Toolbox.EARTH_RADIUS = 6378137; /* Equitorial Radius instead of 6371000 */
Tier3Toolbox.toRad =
function (num) {
return num * Math.PI / 180;
};
Tier3Toolbox.calculateDistance =
function(lat1, lon1, lat2, lon2){
var dLat = this.toRad(lat2 - lat1);
var dLon = this.toRad(lon2 - lon1);
var a = Math.sin(dLat / 2) * Math.sin(dLat / 2) + Math.cos(this.toRad(lat1)) *
Math.cos(this.toRad(lat2)) * Math.sin(dLon / 2) * Math.sin(dLon / 2);
var distance = this.EARTH_RADIUS * 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
return distance;
}
Javascript has 52 significant bits in a floating point number, it is ~15 significant digits of a floating point number. Java's float has only 24 bits of precision. Remember, that distance formulae contains subtraction. If you subtract two non-precised values, that are close enough, you can obtain a huge error.
Try to change Float into Double: Double.parseDouble().
I am trying to work out he distance between two postcodes. One post code coordinates are generic however the other postcode is stored in the database which i need to get. This code below doesn't work out the distance between the generic postcode and the one i have inputted.
var x = getDistanceFromLatLonInKm(52.482799000000000, -2.000643000000000, 52.48463500000000, -1.980759000000000);
function getDistanceFromLatLonInKm(lat1, lon1, lat2, lon2){
console.log(lat1, lon1, lat2, lon2);
var distanceFromSpecificPoint = getDistanceFromLatLonInKm.bind(null, 52.486637, -1.890952);
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)
}
document.getElementById('result').textContent = x;
console.log(x)
</script>
As per above, you can simply get the value from the database on the server side and use whatever server side web framework you wish. The example I've given here is Classic ASP, purely as an example to show you where the values are entered. Then on the server side, the database values are constants and you only enter the lat/lon for one point and get the distance from the database lat/lon (the constants LAT1/LON1 here). dbModel would be some object on the server side which is populated from the database. You can then grab the latitude/longitude values from this object for insertion into the web page via server side scripting.
function getDistanceFromLatLonInKm(lat, lon) {
const EARTH_RADIUS = 6371; // Radius of the earth in km
// Here's where you would add the value dynamically from the DB.
// I'm using classic ASP here just as an example. You'll have to
// amend for your particular server side web framework, be it
// JSP, MVC, etc.
const LAT1 = <%=dbModel.getLatitude()%>;
const LON1 = <%=dbModel.getLongitude()%>;
console.log(LAT1, LON1, lat, lon);
var dLat = deg2rad(lat - LAT1);
var dLon = deg2rad(lon - LON1);
var a = Math.pow(Math.sin(dLat / 2), 2) + Math.cos(deg2rad(LAT1)) * Math.cos(deg2rad(LON1)) * Math.pow(Math.sin(dLon / 2), 2);
var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
var d = EARTH_RADIUS * c; // Distance in km
return d;
}
function deg2rad(deg) {
return deg * (Math.PI / 180);
}
Or, if you don't require it to be dynamic like this, just grab the static values from the database and enter them here as the values for LAT1 and LON1.
E.g.
const LAT1 = 52.482799;
const LON1 = -2.000643;
Then just call your function like this...
var distance = getDistanceFromLatLonInKm(52.48463500000000, -1.980759000000000);
To do PAF lookups:
FreeMapTools
Google Maps. Just search your postcode, then grab the latitude/longitude from the URL.
I have a list of adresses in my database that i can put into array in JS, but from now I want to display distance between me and them, like
me: Warsaw
array[0]: Berlin
array[1]: Moscov
array[2]: Amsterdam
array[3]: London
(array elements contains precise adresses, examples above are just like pseudocode)
I already made a script that can get distance between 2 points on map, but I am rendering map to do this, and this takes some time so it is not acceptable way if I want to display 20 distance entries at once
It don't have to be distance data as this can be overhelming question, but I just want to know how to fetch any data without waiting the time of map rendering.
Why are you using the map at all for this? There are other approaches you can use.
See here: http://www.movable-type.co.uk/scripts/latlong.html
I've used the "haversine" method myself:
function haversine() {
var radians = Array.prototype.map.call(arguments, function(deg) { return deg/180.0 * Math.PI; });
var lat1 = radians[0], lon1 = radians[1], lat2 = radians[2], lon2 = radians[3];
var R = 6372.8; // km
var dLat = lat2 - lat1;
var dLon = lon2 - lon1;
var a = Math.sin(dLat / 2) * Math.sin(dLat /2) + Math.sin(dLon / 2) * Math.sin(dLon /2) * Math.cos(lat1) * Math.cos(lat2);
var c = 2 * Math.asin(Math.sqrt(a));
return R * c;
}
console.log(haversine(36.12, -86.67, 33.94, -118.40));
Is it possible to get nearby places, providing the Latitude and Longitude?
If, for example, I would like places around the provided Lat, Long within the range of 50 kms, how do I go about achieving that?
Is there any algorithm / formula ?
I'm using OpenStreetMap geolocations
Thank you.
You can use below formula to calculate distance between two given co-ordinates:
(lat1, lon1) and (lat2, lon2)
dist = arccos(sin(lat1) · sin(lat2) + cos(lat1) · cos(lat2) · cos(lon1 - lon2)) · R
Reference: Great-circle_distance
Now lets say you have all these co-ordinates saved in database, then you can run a query to find all the locations that are within 50km of range.
SELECT * FROM Places WHERE acos(sin(1.3963) * sin(Lat) + cos(1.3963) * cos(Lat) * cos(Lon - (-0.6981))) * 6371 <= 50;
It is also possible to do this in Javascript. You need to use some Math functions and iterate through an array which stores the co-oridinate to check the distance.
I think you can use this formula to find the distance between 2 points based on lat/lng. You can then use it for your purpose:
var kmBetween = function(a, b){
var e = Math, ra = e.PI/180;
var b = b.lat * ra, c = a.lat * ra, d = b - c;
var g = b.lng * ra - a.lng * ra;
var f = 2 * e.asin(e.sqrt(e.pow(e.sin(d/2), 2) + e.cos(b) * e.cos(c) * e.pow(e.sin(g/2), 2)));
return f * 6378.137;
}
var distance = kmBetween({
lat: 45.5,
lng: 33.4
},
{
lat: 44.3,
lng: 32.4
});