问题
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.
回答1:
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!!
回答2:
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