给定表示目标的长/纬度坐标数据库和表示代表“区域”的多边形的边界坐标的一系列纬度/经度。使用简单的光线投射算法,将纬度/经度作为笛卡尔坐标处理以确定目标是否在区域内是安全的吗?
答案 0 :(得分:3)
如果边缘很短,它应该足够好。但它不会是“正确的”。
想象一个三角形,赤道上有两个点a和b,另一个距离北极点不足。显然,(几乎)赤道上方a和b之间的经度都在三角形中。但是如果我们尝试将拉特/长点作为笛卡尔坐标来处理,我们会得到一些完全不同的东西......
编辑:您需要小心跨越经度=最大/分钟的区域,并且更加小心那些也包含极点的区域
答案 1 :(得分:1)
你可以试试这个
<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">
<title></title>
<script type="text/javascript" src="https://maps.googleapis.com/maps/api/js?key=AIzaSyBfaExFhABnh7I3-vTHJjA4TWqtYnMccKE&sensor=false"></script>
<script type="text/javascript" src="http://www.the-di-lab.com/polygon/jquery-1.4.2.min.js"></script>
<script type="text/javascript">
var map;
var boundaryPolygon;
function initialize() {
google.maps.Polygon.prototype.Contains = function (point) {
// ray casting alogrithm http://rosettacode.org/wiki/Ray-casting_algorithm
var crossings = 0,
path = this.getPath();
// for each edge
for (var i = 0; i < path.getLength(); i++) {
var a = path.getAt(i),
j = i + 1;
if (j >= path.getLength()) {
j = 0;
}
var b = path.getAt(j);
if (rayCrossesSegment(point, a, b)) {
crossings++;
}
}
// odd number of crossings?
return (crossings % 2 == 1);
function rayCrossesSegment(point, a, b) {
var px = point.lng(),
py = point.lat(),
ax = a.lng(),
ay = a.lat(),
bx = b.lng(),
by = b.lat();
if (ay > by) {
ax = b.lng();
ay = b.lat();
bx = a.lng();
by = a.lat();
}
if (py == ay || py == by) py += 0.00000001;
if ((py > by || py < ay) || (px > Math.max(ax, bx))) return false;
if (px < Math.min(ax, bx)) return true;
var red = (ax != bx) ? ((by - ay) / (bx - ax)) : Infinity;
var blue = (ax != px) ? ((py - ay) / (px - ax)) : Infinity;
return (blue >= red);
}
};
var mapProp = {
center: new google.maps.LatLng(37.684, -122.591),
zoom: 10,
mapTypeId: google.maps.MapTypeId.ROADMAP
};
map = new google.maps.Map(document.getElementById("googleMap"), mapProp);
google.maps.event.addListener(map, 'click', function (event) {
if (boundaryPolygon!=null && boundaryPolygon.Contains(event.latLng)) {
alert(event.latLng + " is inside the polygon");
} else {
alert(event.latLng + " is outside the polygon");
}
});
}
function btnCheckPointExistence_onclick() {
var latitude = document.getElementById('txtLattitude').value;
var longitude = document.getElementById('txtLongitude').value;
//alert(latitude); alert(longitude)
var myPoint = new google.maps.LatLng(latitude, longitude);
if (boundaryPolygon == null) {
alert("No Polygon");
}
else {
if (boundaryPolygon.Contains(myPoint)) {
alert(myPoint + "is inside the polygon.");
} else {
alert(myPoint + "is outside the polygon.");
}
}
}
function drawPolygon() {
initialize();
var boundary = '77.702866 28.987153, 77.699776 28.978594 ,77.735996 28.974164 ,77.719946 28.99346 ,77.713423 28.994361 ,77.711706 28.990382 ';
var boundarydata = new Array();
var latlongs = boundary.split(",");
for (var i = 0; i < latlongs.length; i++) {
latlong = latlongs[i].trim().split(" ");
boundarydata[i] = new google.maps.LatLng(latlong[1], latlong[0]);
}
boundaryPolygon = new google.maps.Polygon({
path: boundarydata,
strokeColor: "#0000FF",
strokeOpacity: 0.8,
strokeWeight: 2,
fillColor: 'Red',
fillOpacity: 0.4
});
google.maps.event.addListener(boundaryPolygon, 'click', function (event) {
if (boundaryPolygon.Contains(event.latLng)) {
alert(event.latLng + "is inside the polygon.");
} else {
alert(event.latLng + "is outside the polygon.");
}
});
map.setZoom(14);
map.setCenter(boundarydata[0]);
boundaryPolygon.setMap(map);
}
</script>
</head>
<body onload="initialize();drawPolygon();">
<form id="form1" runat="server">
<input type="text" value="28.982005022927137" name="txtLattitude" id="txtLattitude" placeholder="Enter Latitude">
<input type="text" value="77.72157669067383" name="txtLongitude" id="txtLongitude" placeholder="Enter Langitude">
<input type="button" value="Submit" name="submit" id="submit-text" value="submit" onclick="btnCheckPointExistence_onclick();">
<h3>Check If Point Exist in a Polygon</h3>
<span id="spnMsg" style="font-family: Arial; text-align: center; font-size: 14px; color: red;">this is message</span>
<br />
<br />
<div id="googleMap" style="width: auto; height: 500px;">
</div>
</form>
</body>
</html>
您可以查看Demo here
答案 2 :(得分:0)
不,这样做并不安全。你会在极点和经度0区域出现异常现象。
看看美国宇航局的世界风代码。虽然你必须小心,但它们在地球表面上有多边形的表示 - 一些表示将代表这些异常,而另一些则不代表。