How to generate a set of geospacial coordinates? - javascript

I tried using this:
function getRandomInRange(from, to, fixed) {
return parseFloat((Math.random() * (to - from) + from).toFixed(fixed));
}
var latLongPairs = 4;
for(var i =0; i<latLongPairs; i++) {
console.log(`${getRandomInRange(-180, 180, 3)}, ${getRandomInRange(-180, 180, 3)}`);
}
That's ok for random numbers like 39.21988,9.124741 but they might end up not valid coordinates. And I need 100 of them.

Your latitude range is incorrect - it should be ±90.
function getRandomInRange(from, to) {
return Math.random() * (to - from) + from;
}
const latLongPairs = 4;
for (let i = 0; i < latLongPairs; ++i) {
let lat = getRandomInRange(-90, 90);
let lon = getRandomInRange(-180, 180);
console.log(`${lat.toFixed(3)}, ${lon.toFixed(3)}`);
}

You might need to provide some initial Latitude and longitude with some radius (in meters)
var getRandomLocation = function(latitude, longitude, radiusInMeters) {
var getRandomCoordinates = function(radius, uniform) {
// Generate two random numbers
var a = Math.random(),
b = Math.random();
// Flip for more uniformity.
if (uniform) {
if (b < a) {
var c = b;
b = a;
a = c;
}
}
// It's all triangles.
return [
b * radius * Math.cos(2 * Math.PI * a / b),
b * radius * Math.sin(2 * Math.PI * a / b)
];
};
var randomCoordinates = getRandomCoordinates(radiusInMeters, true);
// Earths radius in meters via WGS 84 model.
var earth = 6378137;
// Offsets in meters.
var northOffset = randomCoordinates[0],
eastOffset = randomCoordinates[1];
// Offset coordinates in radians.
var offsetLatitude = northOffset / earth,
offsetLongitude = eastOffset / (earth * Math.cos(Math.PI * (latitude / 180)));
return `${latitude + (offsetLatitude * (180 / Math.PI))}, ${longitude + (offsetLongitude * (180 / Math.PI))}`
};
for (i = 0; i < 182; i++) {
console.log(getRandomLocation(41.8819, -87.6278, 50))
}

Related

How to Convert an Array into an Object

I'm trying to make a circle from a radius and x,y coordinate. I have it all done except the array is not the correct format for my use.
I get:
[
"X_PROPS:40,Y_PROPS:0",
"X_PROPS:39.99390780625565,Y_PROPS:0.6980962574913405",
"X_PROPS:39.97563308076383,Y_PROPS:1.3959798681000388",
"X_PROPS:39.94518139018295,Y_PROPS:2.093438249717753"
]
but I need:
[
{X_PROPS:40,Y_PROPS:0},
{X_PROPS:39.99390780625565,Y_PROPS:0.6980962574913405},
{X_PROPS:39.97563308076383,Y_PROPS:1.3959798681000388},
{X_PROPS:39.94518139018295,Y_PROPS:2.093438249717753}
]
I tried this:
function spec(radius, steps, centerX, centerY){
var xValues = [centerX];
var yValues = [centerY];
var result = [];
for (var i = 0; i < steps; i++) {
xValues[i] = (centerX + radius * Math.cos(2 * Math.PI * i / steps));
yValues[i] = (centerY + radius * Math.sin(2 * Math.PI * i / steps));
result.push('X_PROPS:'+ xValues[i]+','+'Y_PROPS:'+ yValues[i]);
}
return result;
}
console.log(spec(40,360,0,0))
This expression 'X_PROPS:'+ xValues[i]+','+'Y_PROPS:'+ yValues[i] creates a string. Create an object literal instead:
function spec(radius, steps, centerX, centerY) {
var result = [];
for (var i = 0; i < steps; i++) {
result.push({
X_PROPS: (centerX + radius * Math.cos(2 * Math.PI * i / steps)),
Y_PROPS: (centerY + radius * Math.sin(2 * Math.PI * i / steps))
});
}
return result;
}
console.log(spec(40, 360, 0, 0))

JSON.stringify puts quotes around my float

My question probably has an easy answer but I can't seem to find a solution for my problem.
I have some code to do a put request to the phillips hue api and it requires:
{"xy":[0.300,0.300]} but JSON.stringify() returns {"xy":["0.300","0.300"]}
how can I get it to return the correct values?
Here is my code:
function AllRed() {
var url = 'http://192.168.168.124/api/husm18zj4JGeeHxoUKwDrCVfKRw6nicB25dLnYHX/groups/*/action';
var r = 255;
var g = 0;
var b = 0;
var model = 'LCT001';
var data = JSON.stringify({'xy': RGBtoXY(r, g, b, model)});//RGBtoXY(r, g, b, model)
$.put(url, data);
}
And here is the code for RGBtoXY which I got from another thread here on stackoverflow, unfortunately I can't find the specific thread anymore.
function XYPoint(x, y)
{
if (this instanceof XYPoint)
{
this.x = x;
this.y = y;
} else
{
return new XYPoint(x, y);
}
}
/**
* Get Color points according to light model
* #param model string Ex: LLC010
* #returns {Array}
*/
function colorPointsForModel(model)
{
var colorPoints = [];
if (model === 'LCT001')
{
colorPoints.push(XYPoint(0.500, 0.322));
colorPoints.push(XYPoint(0.4091, 0.518));
colorPoints.push(XYPoint(0.167, 0.04));
} else if (model === 'LLC006' || model === 'LLC007')
{
colorPoints.push(XYPoint(0.704, 0.296));
colorPoints.push(XYPoint(0.2151, 0.7106));
colorPoints.push(XYPoint(0.138, 0.08));
} else
{
// Default construct triangle wich contains all values
colorPoints.push(XYPoint(1.0, 0.0));
colorPoints.push(XYPoint(0.0, 1.0));
colorPoints.push(XYPoint(0.0, 0.0));
}
return colorPoints;
}
/**
* Method to see if the given XY value is within the reach of the lamps.
*
* #param p the point containing the X,Y value
* #param colorPoints color points array containing RGB XYPoints
* #return true if within reach, false otherwise.
*/
function checkPointInLampsReach(p, colorPoints)
{
var red = colorPoints[0];
var green = colorPoints[1];
var blue = colorPoints[2];
var v1 = XYPoint(green.x - red.x, green.y - red.y);
var v2 = XYPoint(blue.x - red.x, blue.y - red.y);
var q = XYPoint(p.x - red.x, p.y - red.y);
var s = crossProduct(q, v2) / crossProduct(v1, v2);
var t = crossProduct(v1, q) / crossProduct(v1, v2);
return ((s >= 0.0) && (t >= 0.0) && (s + t <= 1.0));
}
/**
* Is Not a number?
* Note: NaN is the only JavaScript value that is treated as unequal to itself
* #param val
* #returns {boolean}
*/
function isNaN(val)
{
return val !== val;
}
/**
* Calculates crossProduct of two 2D vectors / points.
*
* #param p1 first point used as vector
* #param p2 second point used as vector
* #return crossProduct of vectors
*/
function crossProduct(p1, p2)
{
return (p1.x * p2.y - p1.y * p2.x);
}
/**
* Converts RGB to XY and Brightness
* #param r integer 0-255
* #param g integer 0-255
* #param b integer 0-255
* #param model string
*/
function RGBtoXY(red, green, blue, model)
{
if (red > 1 || green > 1 || blue > 1)
{
red /= 255;
green /= 255;
blue /= 255;
}
red = (red > 0.04045) ? Math.pow((red + 0.055) / (1.0 + 0.055), 2.4) : (red / 12.92);
green = (green > 0.04045) ? Math.pow((green + 0.055) / (1.0 + 0.055), 2.4) : (green / 12.92);
blue = (blue > 0.04045) ? Math.pow((blue + 0.055) / (1.0 + 0.055), 2.4) : (blue / 12.92);
var X = red * 0.649926 + green * 0.103455 + blue * 0.197109;
var Y = red * 0.234327 + green * 0.743075 + blue * 0.022598;
var Z = red * 0.0000000 + green * 0.053077 + blue * 1.035763;
var cx = X / (X + Y + Z);
var cy = Y / (X + Y + Z);
if (isNaN(cx)) {
cx = 0.0;
}
if (isNaN(cy)) {
cy = 0.0;
}
//Check if the given XY value is within the colourreach of our lamps.
var xyPoint = XYPoint(cx, cy);
var colorPoints = colorPointsForModel(model);
var inReachOfLamps = checkPointInLampsReach(xyPoint, colorPoints);
if (!inReachOfLamps)
{
//It seems the colour is out of reach
//let's find the closest colour we can produce with our lamp and send this XY value out.
//Find the closest point on each line in the triangle.
var pAB = getClosestPointToPoints(colorPoints[cptRED], colorPoints[cptGREEN], xyPoint);
var pAC = getClosestPointToPoints(colorPoints[cptBLUE], colorPoints[cptRED], xyPoint);
var pBC = getClosestPointToPoints(colorPoints[cptGREEN], colorPoints[cptBLUE], xyPoint);
//Get the distances per point and see which point is closer to our Point.
var dAB = getDistanceBetweenTwoPoints(xyPoint, pAB);
var dAC = getDistanceBetweenTwoPoints(xyPoint, pAC);
var dBC = getDistanceBetweenTwoPoints(xyPoint, pBC);
var lowest = dAB;
var closestPoint = pAB;
if (dAC < lowest) {
lowest = dAC;
closestPoint = pAC;
}
if (dBC < lowest) {
lowest = dBC;
closestPoint = pBC;
}
//Change the xy value to a value which is within the reach of the lamp.
cx = closestPoint.x;
cy = closestPoint.y;
}
retval = [cx.toPrecision(3), cy.toPrecision(3)];
return retval;
}
/**
* Find the closest point on a line.
* This point will be within reach of the lamp.
*
* #param A the point where the line starts
* #param B the point where the line ends
* #param P the point which is close to a line.
* #return the point which is on the line.
*/
function getClosestPointToPoints(A, B, P)
{
var AP = XYPoint(P.x - A.x, P.y - A.y);
var AB = XYPoint(B.x - A.x, B.y - A.y);
var ab2 = AB.x * AB.x + AB.y * AB.y;
var ap_ab = AP.x * AB.x + AP.y * AB.y;
var t = ap_ab / ab2;
if (t < 0.0) {
t = 0.0;
} else if (t > 1.0) {
t = 1.0;
}
return XYPoint(A.x + AB.x * t, A.y + AB.y * t);
}
/**
* Find the distance between two points.
*
* #param one
* #param two
* #return the distance between point one and two
*/
// + (float)getDistanceBetweenTwoPoints:(CGPoint)one point2:(CGPoint)two {
function getDistanceBetweenTwoPoints(one, two)
{
var dx = one.x - two.x; // horizontal difference
var dy = one.y - two.y; // vertical difference
return Math.sqrt(dx * dx + dy * dy);
}
function XYtoRGB(x, y, brightness, model)
{
var xy = XYPoint(x, y);
var colorPoints = colorPointsForModel(model);
var inReachOfLamps = checkPointInLampsReach(xy, colorPoints);
console.log('inReachOfLamps', inReachOfLamps);
if (!inReachOfLamps) {
//It seems the colour is out of reach
//let's find the closest colour we can produce with our lamp and send this XY value out.
//Find the closest point on each line in the triangle.
var pAB = getClosestPointToPoints(colorPoints[cptRED], colorPoints[cptGREEN], xy);
var pAC = getClosestPointToPoints(colorPoints[cptBLUE], colorPoints[cptRED], xy);
var pBC = getClosestPointToPoints(colorPoints[cptGREEN], colorPoints[cptBLUE], xy);
//Get the distances per point and see which point is closer to our Point.
var dAB = getDistanceBetweenTwoPoints(xy, pAB);
var dAC = getDistanceBetweenTwoPoints(xy, pAC);
var dBC = getDistanceBetweenTwoPoints(xy, pBC);
var lowest = dAB;
var closestPoint = pAB;
if (dAC < lowest) {
lowest = dAC;
closestPoint = pAC;
}
if (dBC < lowest) {
lowest = dBC;
closestPoint = pBC;
}
//Change the xy value to a value which is within the reach of the lamp.
xy.x = closestPoint.x;
xy.y = closestPoint.y;
}
var x = xy.x;
var y = xy.y;
var z = 1.0 - x - y;
var Y = brightness;
var X = (Y / y) * x;
var Z = (Y / y) * z;
var r = X * 3.2410 - Y * 1.5374 - Z * 0.4986;
var g = -X * 0.9692 + Y * 1.8760 + Z * 0.0416;
var b = X * 0.0556 - Y * 0.2040 + Z * 1.0570;
r = r <= 0.0031308 ? 12.92 * r : (1.0 + 0.055) * Math.pow(r, (1.0 / 2.4)) - 0.055;
g = g <= 0.0031308 ? 12.92 * g : (1.0 + 0.055) * Math.pow(g, (1.0 / 2.4)) - 0.055;
b = b <= 0.0031308 ? 12.92 * b : (1.0 + 0.055) * Math.pow(b, (1.0 / 2.4)) - 0.055;
if (r < 0)
{
r = 0;
}
if (g < 0)
{
g = 0;
}
if (b < 0)
{
b = 0;
}
if (r > 1 || g > 1 || b > 1)
{
var max = Math.max(r, g, b);
r /= max;
g /= max;
b /= max;
}
r *= 255;
g *= 255;
b *= 255;
r = Math.round(r);
g = Math.round(g);
b = Math.round(b);
return {
r: r,
g: g,
b: b
};
}
Your "problem" is this line
retval = [cx.toPrecision(3), cy.toPrecision(3)];
As already noted in comments toPrecision() returns a string, which when serialized will result in the ".
So either drop the toPrecision() calls here, or convert to a number again later:
var xy = RGBtoXY(r, g, b, model);
// convert to numbers again
xy = xy.map( Number );
var data = JSON.stringify({'xy': xy });//RGBtoXY(r, g, b, model)

Measuring area with n amount of gps coordinates

I need to be able to measure area with n amount amount of gps coordinates using javascript / jquery. I was not able to find this done using javascript or with n amount of coordinates so I decided to ask if anyone knows how to?
One example would be that I have 6 seperate lat / lon coordinates which I need to use to measure their area in square meters.
Any help? :)
This solution will only work for convex polygons formed from latitude/longitude points. The majority of the work is in rearranging the latitude/longitude points in counter-clockwise order. Once the reordering is done, you can find the area of the irregular polygon easily.
//make sure to add the first term to the end of both arrays
// ---------------SAME---------------
// | |
var lats = [25.767368, 34.088808, 40.727093, 25.767368];
// | |
var lons = [-80.18930, -118.40612, -73.97864, -80.18930];
//get the average center point of the polygon
var lats_sum = 0;
var lons_sum = 0;
for (var i=lats.length; i--;) {
lats_sum += lats[i];
lons_sum += lons[i];
}
var lat_origin = lats_sum / lats.length;
var lon_origin = lons_sum / lons.length;
//translate origin to (0,0) by shifting lat lons
//and calculate the standard angle of the point
var angles = new Array(lats.length);
for (var j=lats.length; j--;) {
lats[j] -= lat_origin;
lons[j] -= lon_origin;
if (lons[j] >= 0 && lats[j] >= 0) {
angles[j] = Math.abs(Math.atan(lats[j]/lons[j]) * 180 / Math.PI);
} else if (lons[j] < 0 && lats[j] >= 0) {
angles[j] = 90 + Math.abs(Math.atan(lats[j]/lons[j]) * 180 / Math.PI);
} else if (lons[j] < 0 && lats[j] < 0) {
angles[j] = 180 + Math.abs(Math.atan(lats[j]/lons[j]) * 180 / Math.PI);
} else if (lons[j] >= 0 && lats[j] < 0) {
angles[j] = 270 + Math.abs(Math.atan(lats[j]/lons[j]) * 180 / Math.PI);
}
}
//re-arrange the points from least to greatest angle
var cur_ang, cur_lat, cur_lon;
for (var l = 0; l < angles.length; l++) {
for (var k = 0; k < angles.length - 1; k++) {
cur_ang = angles[k];
cur_lat = lats[k];
cur_lon = lons[k];
if (cur_ang < angles[k+1]) {
angles[k] = angles[k+1];
lats[k] = lats[k+1];
lons[k] = lons[k+1];
angles[k+1] = cur_ang;
lats[k+1] = cur_lat;
lons[k+1] = cur_lon;
}
}
}
//calculate area for irregular polygon
var sum1 = 0;
var sum2 = 0;
for (var t = 0; t < lats.length; t++) {
if (t != lats.length - 1) {
sum1 += lats[t] * lons[t+1];
sum2 += lons[t] * lats[t+1];
} else {
sum1 += lats[t] * lons[0];
sum2 += lons[t] * lats[0];
}
}
var area = (sum1 - sum2) / 2.0;
console.log("Area: " + area);
Then when it comes to converting that lat lon area to meters squared I have no idea. This is a function I found online that may help you get a start.
// Use to convert from lat long dist to meters
function measure(lat1, lon1, lat2, lon2){ // generally used geo measurement function
var R = 6378.137; // Radius of earth in KM
var dLat = (lat2 - lat1) * Math.PI / 180;
var dLon = (lon2 - lon1) * Math.PI / 180;
var a = Math.sin(dLat/2) * Math.sin(dLat/2) +
Math.cos(lat1 * Math.PI / 180) * Math.cos(lat2 * Math.PI / 180) *
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 * 1000; // meters
}

Find a point in a polyline which is closest to a latlng

i have a polyine which i have drawn with latlngs obtained from google maps directions service.
Now i want to find a point on the polyline that is closest to a given point.
The obvious way (to me) is to kind of loop through all the points in the polyline and find the distance between them and the given point, however this is inefficient because the points on the polyline can potentially be large.
I would be glad to hear any alternatives of doing this.
Thanks in advance.
I needed a cleaner version that was ported to V3, so here it is:
/**
* Snap marker to closest point on a line.
*
* Based on Distance to line example by
* Marcelo, maps.forum.nu - http://maps.forum.nu/gm_mouse_dist_to_line.html
* Then
* # work of Björn Brala - Swis BV who wrapped the algorithm in a class operating on GMap Objects
* And now
* Bill Chadwick, who factored the basic algorithm out of the class (removing much intermediate storage of results)
* and added distance along line to nearest point calculation
* Followed by
* Robert Crowe, who ported it to v3 of the Google Maps API and factored out the marker to make it more general.
*
* Usage:
*
* Create the class
* var oSnap = new cSnapToRoute();
*
* Initialize the subjects
* oSnap.init(oMap, oPolyline);
*
**/
function cSnapToRoute() {
this.routePoints = Array();
this.routePixels = Array();
this._oMap;
this._oPolyline;
/**
* #desc Initialize the objects.
* #param Map object
* #param GPolyline object - the 'route'
**/
this.init = function (oMap, oPolyline) {
this._oMap = oMap;
this._oPolyline = oPolyline;
this.loadRouteData(); // Load needed data for point calculations
}
/**
* #desc internal use only, Load route points into RoutePixel array for calculations, do this whenever zoom changes
**/
this.loadRouteData = function () {
this.routePixels = new Array();
var proj = this._oMap.getProjection();
for (var i = 0; i < this._oPolyline.getPath().getLength(); i++) {
var Px = proj.fromLatLngToPoint(this._oPolyline.getPath().getAt(i));
this.routePixels.push(Px);
}
}
/**
* #desc Get closest point on route to test point
* #param GLatLng() the test point
* #return new GLatLng();
**/
this.getClosestLatLng = function (latlng) {
var r = this.distanceToLines(latlng);
var proj = this._oMap.getProjection();
return proj.fromPointToLatLng(new google.maps.Point(r.x, r.y));
}
/**
* #desc Get distance along route in meters of closest point on route to test point
* #param GLatLng() the test point
* #return distance in meters;
**/
this.getDistAlongRoute = function (latlng) {
var r = this.distanceToLines(latlng);
return this.getDistToLine(r.i, r.fTo);
}
/**
* #desc internal use only, gets test point xy and then calls fundamental algorithm
**/
this.distanceToLines = function (thisLatLng) {
var tm = this._oMap;
var proj = this._oMap.getProjection();
var thisPx = proj.fromLatLngToPoint(thisLatLng);
var routePixels = this.routePixels;
return getClosestPointOnLines(thisPx, routePixels);
}
/**
* #desc internal use only, find distance along route to point nearest test point
**/
this.getDistToLine = function (iLine, fTo) {
var routeOverlay = this._oPolyline;
var d = 0;
for (var n = 1 ; n < iLine ; n++) {
d += routeOverlay.getPath().getAt(n - 1).distanceFrom(routeOverlay.getPath().getAt(n));
}
d += routeOverlay.getPath().getAt(iLine - 1).distanceFrom(routeOverlay.getPath().getAt(iLine)) * fTo;
return d;
}
}
/* desc Static function. Find point on lines nearest test point
test point pXy with properties .x and .y
lines defined by array aXys with nodes having properties .x and .y
return is object with .x and .y properties and property i indicating nearest segment in aXys
and property fFrom the fractional distance of the returned point from aXy[i-1]
and property fTo the fractional distance of the returned point from aXy[i] */
function getClosestPointOnLines(pXy, aXys) {
var minDist;
var fTo;
var fFrom;
var x;
var y;
var i;
var dist;
if (aXys.length > 1) {
for (var n = 1 ; n < aXys.length ; n++) {
if (aXys[n].x != aXys[n - 1].x) {
var a = (aXys[n].y - aXys[n - 1].y) / (aXys[n].x - aXys[n - 1].x);
var b = aXys[n].y - a * aXys[n].x;
dist = Math.abs(a * pXy.x + b - pXy.y) / Math.sqrt(a * a + 1);
}
else
dist = Math.abs(pXy.x - aXys[n].x)
// length^2 of line segment
var rl2 = Math.pow(aXys[n].y - aXys[n - 1].y, 2) + Math.pow(aXys[n].x - aXys[n - 1].x, 2);
// distance^2 of pt to end line segment
var ln2 = Math.pow(aXys[n].y - pXy.y, 2) + Math.pow(aXys[n].x - pXy.x, 2);
// distance^2 of pt to begin line segment
var lnm12 = Math.pow(aXys[n - 1].y - pXy.y, 2) + Math.pow(aXys[n - 1].x - pXy.x, 2);
// minimum distance^2 of pt to infinite line
var dist2 = Math.pow(dist, 2);
// calculated length^2 of line segment
var calcrl2 = ln2 - dist2 + lnm12 - dist2;
// redefine minimum distance to line segment (not infinite line) if necessary
if (calcrl2 > rl2)
dist = Math.sqrt(Math.min(ln2, lnm12));
if ((minDist == null) || (minDist > dist)) {
if (calcrl2 > rl2) {
if (lnm12 < ln2) {
fTo = 0;//nearer to previous point
fFrom = 1;
}
else {
fFrom = 0;//nearer to current point
fTo = 1;
}
}
else {
// perpendicular from point intersects line segment
fTo = ((Math.sqrt(lnm12 - dist2)) / Math.sqrt(rl2));
fFrom = ((Math.sqrt(ln2 - dist2)) / Math.sqrt(rl2));
}
minDist = dist;
i = n;
}
}
var dx = aXys[i - 1].x - aXys[i].x;
var dy = aXys[i - 1].y - aXys[i].y;
x = aXys[i - 1].x - (dx * fTo);
y = aXys[i - 1].y - (dy * fTo);
}
return { 'x': x, 'y': y, 'i': i, 'fTo': fTo, 'fFrom': fFrom };
}
See Bill Chadwick's example here:
http://www.bdcc.co.uk/Gmaps/BdccGmapBits.htm
above example ported to v3 (code at bottom of this answer)
on his page under:
DISTANCE POINT TO POLYLINE OR POLYGON
from that post:
There is a similar, better demo here http://wtp2.appspot.com/cSnapToRouteDemo.html
It is finding the closest point on the line to the mouse. Also note that it is a Google Maps API v2 example (but the principle with v3 would be the same).
// Code to find the distance in metres between a lat/lng point and a polyline of lat/lng points
// All in WGS84. Free for any use.
//
// Bill Chadwick 2007
// updated to Google Maps API v3, Lawrence Ross 2014
// Construct a bdccGeo from its latitude and longitude in degrees
function bdccGeo(lat, lon)
{
var theta = (lon * Math.PI / 180.0);
var rlat = bdccGeoGeocentricLatitude(lat * Math.PI / 180.0);
var c = Math.cos(rlat);
this.x = c * Math.cos(theta);
this.y = c * Math.sin(theta);
this.z = Math.sin(rlat);
}
bdccGeo.prototype = new bdccGeo();
// internal helper functions =========================================
// Convert from geographic to geocentric latitude (radians).
function bdccGeoGeocentricLatitude(geographicLatitude)
{
var flattening = 1.0 / 298.257223563;//WGS84
var f = (1.0 - flattening) * (1.0 - flattening);
return Math.atan((Math.tan(geographicLatitude) * f));
}
// Returns the two antipodal points of intersection of two great
// circles defined by the arcs geo1 to geo2 and
// geo3 to geo4. Returns a point as a Geo, use .antipode to get the other point
function bdccGeoGetIntersection( geo1, geo2, geo3, geo4)
{
var geoCross1 = geo1.crossNormalize(geo2);
var geoCross2 = geo3.crossNormalize(geo4);
return geoCross1.crossNormalize(geoCross2);
}
//from Radians to Meters
function bdccGeoRadiansToMeters(rad)
{
return rad * 6378137.0; // WGS84 Equatorial Radius in Meters
}
//from Meters to Radians
function bdccGeoMetersToRadians(m)
{
return m / 6378137.0; // WGS84 Equatorial Radius in Meters
}
// properties =================================================
bdccGeo.prototype.getLatitudeRadians = function()
{
return (bdccGeoGeographicLatitude(Math.atan2(this.z,
Math.sqrt((this.x * this.x) + (this.y * this.y)))));
}
bdccGeo.prototype.getLongitudeRadians = function()
{
return (Math.atan2(this.y, this.x));
}
bdccGeo.prototype.getLatitude = function()
{
return this.getLatitudeRadians() * 180.0 / Math.PI;
}
bdccGeo.prototype.getLongitude = function()
{
return this.getLongitudeRadians() * 180.0 / Math.PI ;
}
// Methods =================================================
//Maths
bdccGeo.prototype.dot = function( b)
{
return ((this.x * b.x) + (this.y * b.y) + (this.z * b.z));
}
//More Maths
bdccGeo.prototype.crossLength = function( b)
{
var x = (this.y * b.z) - (this.z * b.y);
var y = (this.z * b.x) - (this.x * b.z);
var z = (this.x * b.y) - (this.y * b.x);
return Math.sqrt((x * x) + (y * y) + (z * z));
}
//More Maths
bdccGeo.prototype.scale = function( s)
{
var r = new bdccGeo(0,0);
r.x = this.x * s;
r.y = this.y * s;
r.z = this.z * s;
return r;
}
// More Maths
bdccGeo.prototype.crossNormalize = function( b)
{
var x = (this.y * b.z) - (this.z * b.y);
var y = (this.z * b.x) - (this.x * b.z);
var z = (this.x * b.y) - (this.y * b.x);
var L = Math.sqrt((x * x) + (y * y) + (z * z));
var r = new bdccGeo(0,0);
r.x = x / L;
r.y = y / L;
r.z = z / L;
return r;
}
// point on opposite side of the world to this point
bdccGeo.prototype.antipode = function()
{
return this.scale(-1.0);
}
//distance in radians from this point to point v2
bdccGeo.prototype.distance = function( v2)
{
return Math.atan2(v2.crossLength(this), v2.dot(this));
}
//returns in meters the minimum of the perpendicular distance of this point from the line segment geo1-geo2
//and the distance from this point to the line segment ends in geo1 and geo2
bdccGeo.prototype.distanceToLineSegMtrs = function(geo1, geo2)
{
//point on unit sphere above origin and normal to plane of geo1,geo2
//could be either side of the plane
var p2 = geo1.crossNormalize(geo2);
// intersection of GC normal to geo1/geo2 passing through p with GC geo1/geo2
var ip = bdccGeoGetIntersection(geo1,geo2,this,p2);
//need to check that ip or its antipode is between p1 and p2
var d = geo1.distance(geo2);
var d1p = geo1.distance(ip);
var d2p = geo2.distance(ip);
//window.status = d + ", " + d1p + ", " + d2p;
if ((d >= d1p) && (d >= d2p))
return bdccGeoRadiansToMeters(this.distance(ip));
else
{
ip = ip.antipode();
d1p = geo1.distance(ip);
d2p = geo2.distance(ip);
}
if ((d >= d1p) && (d >= d2p))
return bdccGeoRadiansToMeters(this.distance(ip));
else
return bdccGeoRadiansToMeters(Math.min(geo1.distance(this),geo2.distance(this)));
}
// distance in meters from GLatLng point to GPolyline or GPolygon poly
function bdccGeoDistanceToPolyMtrs(poly, point)
{
var d = 999999999;
var i;
var p = new bdccGeo(point.lat(),point.lng());
for(i=0; i<(poly.getPath().getLength()-1); i++)
{
var p1 = poly.getPath().getAt(i);
var l1 = new bdccGeo(p1.lat(),p1.lng());
var p2 = poly.getPath().getAt(i+1);
var l2 = new bdccGeo(p2.lat(),p2.lng());
var dp = p.distanceToLineSegMtrs(l1,l2);
if(dp < d)
d = dp;
}
return d;
}
// get a new GLatLng distanceMeters away on the compass bearing azimuthDegrees
// from the GLatLng point - accurate to better than 200m in 140km (20m in 14km) in the UK
function bdccGeoPointAtRangeAndBearing (point, distanceMeters, azimuthDegrees)
{
var latr = point.lat() * Math.PI / 180.0;
var lonr = point.lng() * Math.PI / 180.0;
var coslat = Math.cos(latr);
var sinlat = Math.sin(latr);
var az = azimuthDegrees* Math.PI / 180.0;
var cosaz = Math.cos(az);
var sinaz = Math.sin(az);
var dr = distanceMeters / 6378137.0; // distance in radians using WGS84 Equatorial Radius
var sind = Math.sin(dr);
var cosd = Math.cos(dr);
return new google.maps.LatLng(Math.asin((sinlat * cosd) + (coslat * sind * cosaz)) * 180.0 / Math.PI,
(Math.atan2((sind * sinaz), (coslat * cosd) - (sinlat * sind * cosaz)) + lonr) * 180.0 / Math.PI);
}
I do not think you can avoid checking all the points.
What if the not checked point is the nearest one?
If you have to do this operation many times, you can choose a data structure that is optimized for such a search, quadtree for example.
Note that you should not use lat lng as Descartes coordinates.
See also Finding nearest point in an efficient way
That is for the 2D plane, and not for lat lng, but you can approximate: https://stackoverflow.com/a/16271669/59019
Inspired by jmihalicza's answer, i came up with this function to find the closest point in an array of LatLngs to a given LatLng.
function closest takes a LatLng(llng) and an array of LatLngs (listData) and finds the distance between each latlng in the array and the given latlng, it then finds the least distance and returns the Latlng from the list which provided that distance.
function closest(llng, listData) {
var arr = listData;
var pnt = llng;
var distArr = [];
var dist = google.maps.geometry.spherical.computeDistanceBetween;
for (index in arr)
distArr.push([arr[index], dist(pnt, arr[index])]);
return distArr.sort(function(a,b){
return a[1]-b[1];
})[0][0];
}
EDIT
If you don't have access to the array of LatLngs which make up the polyline, but have access to the polyline itself, you can use polyline's getPath method to get the path which is an MVC array so you can use .getArray() to return an array of LatLngs to use with the above function (closest).

Circle radius on Lat/Lng map

I am trying to draw a circle on a CloudMade map. The center of the circle is expressed in Lat/Lng, while the radius is in meters. Here following is the JavaScript I use, but some tests seem to indictae that the conversion I'm using for the radius gives me a too short radius. Does somebody understand what I', doing wrong?
function DrawCircle (center, radius)
{
var circlePoints = Array();
with (Math)
{
var d = radius/6371000; // radians
var lat1 = (PI/180) * center.lat(); // radians
var lng1 = (PI/180) * center.lng(); // radians
for (var a = 0; a <= 360; a++)
{
var tc = (PI/180) * a;
var y = asin(sin(lat1) * cos(d) + cos(lat1) * sin(d) * cos(tc));
var dlng = atan2(sin(tc) * sin(d) * cos(lat1), cos(d) - sin(lat1) * sin(y));
var x = ((lng1 - dlng + PI) % (2 * PI)) - PI ; // MOD function
var point = new CM.LatLng(parseFloat(y * (180/PI)), parseFloat(x * (180/PI)));
circlePoints.push(point);
}
circle = new CM.Polygon(circlePoints, circleBorderColor, circleBorderWidth, circleBorderOpacity, circleFillColor, circleFillOpacity);
map.addOverlay(circle);
}
}

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