I am trying to get geo combinations of a grid which is covered a certain area (My city). The grid is 500m * 500m. So I wanna enter starting long/latitude combination,distance (500m), degree (90 or 270) and get the next long/latitude combination.
I am so unaware of mathematical formulas, and hard to find a solution. I had found some php functions that return distance in between two long/latitude combinations.
http://www.zipcodeworld.com/samples/distance.php.html http://www.phpro.org/tutorials/Geo-Targetting-With-PHP-And-MySQL.html#3
But still I cannot rebuild this thing according to my need (I really hate cos,sin,tan). Really appreciate if someone help me over this.
Here is the code for finding four extreme points (lat, long) around a center point
<script type="text/javascript">
function toRad (value) {
return value * Math.PI / 180;
}
function toDeg (value) {
return value * 180 / Math.PI;
}
function computePoint(){
var radius = 6371; //in kms
var lat1 = checkField(document.getElementById("lat"));
var lon1 = checkField(document.getElementById("long"));
var dist = document.getElementById("distance").value;
dist = typeof(dist)=='number' ? dist : typeof(dist)=='string' && dist.trim()!='' ? +dist : NaN;
// alert("Dist "+ dist+" kms");
var angularDist = dist / radius;
lat1= toRad(lat1);
lon1=toRad(lon1);
var lat2,lon2, angle = 0;
for(i=1; i<5; i++,angle+=90){
var brng = toRad(angle);
lat2=lon2=0;
// second latitude
lat2 = Math.asin(Math.sin(lat1) * Math.cos(angularDist) +
Math.cos(lat1) * Math.sin(angularDist) * Math.cos(brng));
// second longitude
lon2 = lon1 + Math.atan2(Math.sin(brng) * Math.sin(angularDist) *
Math.cos(lat1), Math.cos(angularDist) - Math.sin(lat1) * Math.sin(lat2));
if (isNaN(lat2) || isNaN(lon2)) alert("Something is null");
// lon2 = (lon2+3*Math.PI) % (2*Math.PI) - Math.PI; // normalise to -180..+180º
lat2 = toDeg(lat2);
lon2 = toDeg(lon2);
// alert("latitude: "+lat2 +",Longitude "+lon2);
document.getElementById("lat"+i).innerHTML=lat2;
document.getElementById("long"+i).innerHTML=lon2;
document.getElementById("ang"+i).innerHTML=angle;
}
}
function checkField(field){
var str=field.name
var latlon1
latlon=field.value;//parselatlon(field.value)
if (str.substring(0,3)=="lat") {
if (latlon > 90.) {
alert ("Latitudes cannot exceed 90 degrees")
field.focus() // Doesn't work!
field.select()
}
}
if (str.substring(0,3)=="long") {
if (latlon > 180.) {
alert ("Longitudes cannot exceed 180 degrees")
field.focus()
field.select()
}
}
return latlon
}
function parselatlon(instr){
// Parse strings dd.dd dd:mm.mm dd:mm:ss.ss
var deg,min,sec,colonIndex,degstr,minstr,str
str=instr
colonIndex=str.indexOf(":")
if (colonIndex==-1){ // dd.dd?
if (!isPosNumber(str)){
badLLFormat(instr)
return 0.
} else {
return parseFloat(str)
}
}
}
function isPosNumber(instr){ //integer or float
str=""+instr // force to string type
oneDecimal=false
for (var i=0;i<str.length;i++) {
var oneChar=str.charAt(i)
if (oneChar=="." && !oneDecimal){
oneDecimal=true
continue
}
if (oneChar < "0" || oneChar > "9") {
return false
}
}
return true
}
function badLLFormat(str){
alert(str+ " is an invalid lat/lon format\n"+
"Use DD.DD DD:MM.MM or DD:MM:SS.SS")
}
</script>
and HTML looks like ....
<body>
<div>Enter the details </div>
Latitude : <input type="text" id="lat" name="lat" value="" /> <br/>
Longitude : <input type="text" id="long" name="long" value="" /> <br/>
<!-- Bearing : <input type="text" id="bearing" name="bearing" value="" placeholder="Enter angle in degrees" /> <br/>-->
Distance : <input type="text" id="distance" name="distance" value="" placeholder ="Enter distance in Kms. " /> <br/>
<input type="submit" value="Find Points" name="findPts" onclick="computePoint();"/>
<div><h3><span> <strong>Results Will be displayed here</strong></span></h3></div>
<table border="1" style="text-align: center">
<tr>
<th>Latitude</th>
<th>Longitude</th>
<th>Angle (in degrees) </th>
</tr>
<tr>
<td><label id="lat1" value=""></label> </td>
<td><label id="long1" value=""></label> </td>
<td><label id="ang1" value=""></label> </td>
</tr>
<tr>
<td><label id="lat2" value=""></label> </td>
<td><label id="long2" value=""></label> </td>
<td><label id="ang2" value=""></label> </td>
</tr>
<tr>
<td><label id="lat3" value=""></label> </td>
<td><label id="long3" value=""></label> </td>
<td><label id="ang3" value=""></label> </td>
</tr>
<tr>
<td><label id="lat4" value=""></label> </td>
<td><label id="long4" value=""></label> </td>
<td><label id="ang4" value=""></label> </td>
</tr>
</table>
</body>
I here by donate my code under GPL.... enjoy!!
This site has example code for many lat/long/distance/bearing calculations:
http://www.movable-type.co.uk/scripts/latlong.html
The formula are:
lat2 = asin(sin(lat1)*cos(d/R) + cos(lat1)*sin(d/R)*cos(θ))
lon2 = lon1 + atan2(sin(θ)*sin(d/R)*cos(lat1), cos(d/R)−sin(lat1)*sin(lat2))
θ is the bearing (in radians, clockwise from north);
d/R is the angular distance (in radians), where d is the distance travelled and R is the earth’s radius
The relevant code you are interested in is in javascript, but should be easy to convert:
var lat2 = Math.asin( Math.sin(lat1)*Math.cos(d/R) +
Math.cos(lat1)*Math.sin(d/R)*Math.cos(brng) );
var lon2 = lon1 + Math.atan2(Math.sin(brng)*Math.sin(d/R)*Math.cos(lat1),
Math.cos(d/R)-Math.sin(lat1)*Math.sin(lat2));
来源：https://stackoverflow.com/questions/8800267/get-longtitude-latitude-combination-based-on-distance-and-degree