I'm using this method to calculate distance between 2 coordinates
http://code.google.com/apis/maps/articles/phpsqlsearch.html#findnearsql
for example i have two coordinates(lat and lng)
first coordinate: 37, -122
second coordinate:37.386337, -122.085823
I get this distance 27.1097282198804(miles) between these coordinates by using the method above.
Please tell me any way to verify this distance?
You can also use the Google Maps API Geometry Library.
firstLatLng = new google.maps.LatLng(37,-122);
secondLatLng = new google.maps.LatLng(37.386337, -122.085823);
distance = google.maps.geometry.spherical.computeDistanceBetween(firstLatLng,secondLatLng);
Related
I have a rectangular polygon and I want to extend the boundaries by 10 km for example.
How would I do that ?
I could use extend method, but how Do I find the distance of 10 km in lat lng ?
So far I have :
bounds = new google.maps.LatLngBounds();
pt = new google.maps.LatLng(lat,lng);
bounds.extend(pt)
It depends on how exact an answer you need.
You could use the following approximation:
Latitude: 1 deg = 110.57 km; Longitude: 1 deg = 111.320 km source: http://en.wikipedia.org/wiki/Latitude
For a more exact formula, you need to check http://www.movable-type.co.uk/scripts/latlong.html . It has various formulas and also some code. You are looking for the section called 'Destination point given distance and bearing from start point'
It depends where you are looking at but a longitude is 111km and a latitude 110km:http://en.m.wikipedia.org/wiki/Latitude.
I'm experimenting with System.Data.Spatial.DbGeography, that I want to use to determine the distance from one coordinate to another (going to be stored in SQL server).
My coordinates are in lat/long, and I got them from Bing Maps (I've tried with coordinates from Google Maps too, with the same result).
var osloCentralStation = DbGeography.FromText("POINT(59.9109 10.7523)", 4326);
var drammen = DbGeography.FromText("POINT(59.7378 10.2050)", 4326);
Console.WriteLine("Distance: {0}km", osloCentralStation.Distance(drammen) / 1000);
Returns:
Distance: 63,4340839088124km
The returned distance is approximately double what it should be.
https://maps.google.com/maps?saddr=59.9109+10.7523&daddr=59.7378+10.2050
Does anybody have any idea as to what's going on?
You're not declaring the element in WKT in the right order.
WKT should be in your case:
POINT(10.2050 59.7378)
See OGC standard here:
http://msdn.microsoft.com/en-us/library/bb933834.aspx
http://en.wikipedia.org/wiki/Well-known_text
And then it has to be declared like:
POINT(LONGITUDE LATITUDE)
Also keep in mind that it won't be the driving distance but the distance by air.
It turns out that lat/long are given as long/lat when creating new DbGeography objects.
I've written a little helper method so that I don't get it wrong again in the future:
private static DbGeography CreateDbGeography(double latitude, double longitude, int srid = 0)
{
var text = string.Format(CultureInfo.InvariantCulture.NumberFormat, "POINT({0} {1})", longitude, latitude);
if (srid > 0)
{
return DbGeography.FromText(text, srid);
}
return DbGeography.FromText(text);
}
I need to retrieve a destination's coordinates using the google maps api directions service. I already have the starting point coordinates, however instead of specifying an ending point in coordinates, I wish to retrieve the coordinates by specifying a distance (in km).
So I guess my question is the following: is it possible to retrieve the destination latlong coordinates (based/calculated on the road's distance and not directional/straight line) by specifying a distance (amount in km) with the directions service or perhaps any alternative way?
I have an image illustration, however unfortunately am unable to attach to this question as I do not have enough reputation. If my question is unclear in any way, or you wish to see the illustration then please contact me and I'll send it off.
I don't think you can do this as the request parameters say that origin and destination parameters are required.
I beliave it will help someone.
There is a method to get coordinates in the google maps library:
google.maps.geometry.spherical.computeOffset(fromCoordinates, distanceInMeters, headingInDegrees)
I believe you are correct. There doesn't seem to be any current method in the api which would allow you to do the following.
Instead I looped through the coordinates returned from the directions service call, and used a function to calculate the distance between coordinates. However even this was not accurate enough as the coordinates returned also seemed to be aggregated and doesn't return an accurate value/distance when calculating the distances between each coordinate as they are aggregated and therefore each coordinate is not necessary along the road.
To work around the above issue, I ended up adding a click event, and plotted the coordinates along the road myself and then stored them in a local json file which I cache and call using an xmlhttprequest.
Fortunately, for my situation I only need to calculate the distance between point A & B on one individual road, so my alternative won't work in cases when you're using multiple or generic roads/locations. You could instead use the first method described, given that you're happy to live with the aggregated data and an in-accurate calculation.
Below are the functions used to calculate the distances between coordinates and then also the final calculation to find the point & coordinates between the final two points. Please note this code relies on and uses jQuery methods.
1. Calculate distance (in meters) between two coordinates
function pointDistance( begin, end )
{
var begin = { lat: begin[0], long: begin[1] },
end = { lat: end[0], long: end[1] };
// General calculations
var earthRadius = 6371, //km
distanceLat = (end.lat - begin.lat).toRad(),
distanceLong = (end.long - begin.long).toRad();
// Convert lats to radiants
begin.lat = begin.lat.toRad();
end.lat = end.lat.toRad();
// Calculation
var a = Math.sin(distanceLat / 2) * Math.sin(distanceLat / 2) +
Math.sin(distanceLong / 2) * Math.sin(distanceLong / 2) * Math.cos(begin.lat) * Math.cos(end.lat);
var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
var distance = (earthRadius * c) - 0.000536;
return (distance * 1000);
}
2. Fetch coordinate of final A-B coordinate (based on percentage remaining). The 'matrix' variable is a json array of coordinates.
function getCoordinates( totalDistance )
{
var lastPoint = { lat: null, long: null },
total = parseFloat(0),
position = { start: null, end: null, distance: 0 };
$(matrix).each(function()
{
if ( lastPoint.lat == null )
{
lastPoint = { lat: this[0], long: this[1] };
return;
}
var distance = pointDistance([lastPoint.lat, lastPoint.long], [this[0], this[1]]);
total = total + distance;
if ( (total / 1000) >= totalDistance )
{
position.start = new google.maps.LatLng(lastPoint.lat, lastPoint.long);
position.end = new google.maps.LatLng(this[0], this[1]);
position.distance = total;
return false;
}
lastPoint = { lat: this[0], long: this[1] };
});
return position;
}
3. Convert numeric degrees to radians
if ( typeof(Number.prototype.toRad) === 'undefined' ) {
Number.prototype.toRad = function() {
return this * Math.PI / 180;
}
}
Hope the following helps any one with the same or simular problem. I haven't investigated this as I've had no need to, but, perhaps if you're dealing with google's paid services, they don't aggregate the data returned by the call?
Ok pretty self explanatory. I'm using google maps and I'm trying to find out if a lat,long point is within a circle of radius say x (x is chosen by the user).
Bounding box will not work for this. I have already tried using the following code:
distlatLng = new google.maps.LatLng(dist.latlng[0],dist.latlng[1]);
var latLngBounds = circle.getBounds();
if(latLngBounds.contains(distlatLng)){
dropPins(distlatLng,dist.f_addr);
}
This still results in markers being places outside the circle.
I'm guess this is some simple maths requiring the calculation of the curvature or an area but I'm not sure where to begin. Any suggestions?
Unfortunately Pythagoras is no help on a sphere. Thus Stuart Beard's answer is incorrect; longitude differences don't have a fixed ratio to metres but depend on the latitude.
The correct way is to use the formula for great circle distances. A good approximation, assuming a spherical earth, is this (in C++):
/** Find the great-circle distance in metres, assuming a spherical earth, between two lat-long points in degrees. */
inline double GreatCircleDistanceInMeters(double aLong1,double aLat1,double aLong2,double aLat2)
{
aLong1 *= KDegreesToRadiansDouble;
aLat1 *= KDegreesToRadiansDouble;
aLong2 *= KDegreesToRadiansDouble;
aLat2 *= KDegreesToRadiansDouble;
double cos_angle = sin(aLat1) * sin(aLat2) + cos(aLat1) * cos(aLat2) * cos(aLong2 - aLong1);
/*
Inaccurate trig functions can cause cos_angle to be a tiny amount
greater than 1 if the two positions are very close. That in turn causes
acos to give a domain error and return the special floating point value
-1.#IND000000000000, meaning 'indefinite'. Observed on VS2008 on 64-bit Windows.
*/
if (cos_angle >= 1)
return 0;
double angle = acos(cos_angle);
return angle * KEquatorialRadiusInMetres;
}
where
const double KPiDouble = 3.141592654;
const double KDegreesToRadiansDouble = KPiDouble / 180.0;
and
/**
A constant to convert radians to metres for the Mercator and other projections.
It is the semi-major axis (equatorial radius) used by the WGS 84 datum (see http://en.wikipedia.org/wiki/WGS84).
*/
const int32 KEquatorialRadiusInMetres = 6378137;
Use Google Maps API geometry library to calculate distance between circle's center and your marker, and then compare it with your radius.
var pointIsInsideCircle = google.maps.geometry.spherical.computeDistanceBetween(circle.getCenter(), point) <= circle.getRadius();
It's very simple. You just have to calculate distance between centre and given point and compare it to radius. You can Get Help to calculate distance between two lat lang from here
The following code works for me: my marker cannot be dragged outside the circle, instead it just hangs at its edge (in any direction) and the last valid position is preserved.
The function is the eventhandler for the markers 'drag' event.
_markerDragged : function() {
var latLng = this.marker.getPosition();
var center = this.circle.getCenter();
var radius = this.circle.getRadius();
if (this.circleBounds.contains(latLng) &&
(google.maps.geometry.spherical.computeDistanceBetween(latLng, center) <= radius)) {
this.lastMarkerPos = latLng;
this._geocodePosition(latLng);
} else {
// Prevent dragging marker outside circle
// see (comments of) http://unserkaiser.com/code/google-maps-marker-check-if-in-circle/
// see http://www.mvjantzen.com/blog/?p=3190 and source code of http://mvjantzen.com/cabi/trips4q2012.html
this.marker.setPosition(this.lastMarkerPos);
}
},
Thanks to http://unserkaiser.com/code/google-maps-marker-check-if-in-circle/
and http://www.mvjantzen.com/blog/?p=3190 .
I've been a bit silly really. Thinking about it we can use Pythagorus' theorem.
We have a maximum distance away from a point (X miles), and two latitudes and two longitudes. If we form a triangle using these then we can solve for the distance from the point.
So say we know point1 with coordinates lat1,lng1 is the center of the circle and point2 with coordinates lat2,lng2 is the point we are trying to decide is in the circle or not.
We form a right angled triangle using a point determined by point1 and point2. This, point3 would have coordinates lat1,lng2 or lat2,lng1 (it doesn't matter which). We then calculate the differences (or if you prefer) distances - latDiff = lat2-lat1 and lngDiff = lng2-lng1
we then calculate the distance from the center using Pythagorus - dist=sqrt(lngDiff^2+latDiff^2).
We have to translate everything into meters so that it works correctly with google maps so miles are multiplied by 1609 (approx) and degrees of latitude/longitude by 111000 (approx). This isn't exactly accurate but it does an adequate job.
Hope that all makes sense.
I'm trying to find a function lng = f(lat) that would help me draw a line between 2 given GPS coordinates, (lat1, lng1) and (lat2, lng2).
I've tried the traditional Cartesian formula y=mx+b where m=(y2-y1)/(x2-x1), but GPS coordinates don't seem to behave that way.
What would be a formula/algorithm that could help me achieve my goal.
PS: I'm using Google Maps API but let's keep this implementation agnostic if possible.
UPDATE: My implementation was wrong and it seems the algorithm is actually working as stated by some of the answers. My bad :(
What you want to do should actually work. Keep in mind however that if north is on top, the horizontal (x) axis is the LONGITUDE and the vertical (y) axis is the LATITUDE (I think you might have confused this).
If you parametrize the line as lat = func(long) you will run into trouble with vertical lines (i.e. those going exactly north south) as the latitude varies while the longitude is fixed.
Therefore I'd rather use another parametrization:
long(alpha) = long_1 + alpha * (long_2 - long_1)
lat(alpha) = lat_1 + alpha * (lat_2 - lat_1)
and vary alpha from 0 to 1.
This will not exactly coincide with a great circle (shortest path on a sphere) but the smaller the region you are looking at, the less noticeable the difference will be (as others posters here pointed out).
Here is a distance formula I use that may help. This is using javascript.
function Distance(lat1, lat2, lon1, lon2) {
var R = 6371; // km
var dLat = toRad(lat2 - lat1);
var dLon = toRad(lon2 - lon1);
var a = Math.sin(dLat / 2) * Math.sin(dLat / 2) + Math.cos(toRad(lat1)) * Math.cos(toRad(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 * 0.621371;
var r = Math.round(d * 100) / 100;
return r;
}
For short distances, where the earth curvature doesn't make a significant difference, it works fine to draw a line using regular two-dimensional geometry.
For longer distances the shortest way between two lines does not project as a straight line on a map, but as a curve. (For example, the shortest way from Sweden to Alaska would be straight over the noth pole, not past Canada and Iceland.) You would have to use three-dimensional geometry to draw a line on a surface of a sphere, then project that onto the map in the same way the earth surface is projected on the map.
Is your goal to find this equation or to actually draw a line?
If the latter, since you're using the Maps API, specify geodesic: true and draw it with a Polyline:
http://code.google.com/apis/maps/documentation/javascript/reference.html#Polyline