AFG/dump1090
3
0
Fork 0
Code Issues Pull requests Packages Projects Releases Wiki Activity

Generate geodesic circles for range rings.

Browse source 
Turns out that OL3's circles aren't geodesic circles so the
ranges are all off if you're anywhere but on the equator.
So generate our own LineStrings that approximate a circle.

Should fix #133
This commit is contained in:
Oliver Jowett 2016-07-24 16:13:04 +01:00
parent a06b13d42a
commit d3565b407e
1 changed files with 27 additions and 1 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

28
public_html/script.js
View file

@ -316,6 +316,30 @@ function end_load_history() {
}
// Make a LineString with 'points'-number points
// that is a closed circle on the sphere such that the
// great circle distance from 'center' to each point is
// 'radius' meters
function make_geodesic_circle(center, radius, points) {
var angularDistance = radius / 6378137.0;
var lon1 = center[0] * Math.PI / 180.0;
var lat1 = center[1] * Math.PI / 180.0;
var geom = new ol.geom.LineString();
for (var i = 0; i <= points; ++i) {
var bearing = i * 2 * Math.PI / points;
var lat2 = Math.asin( Math.sin(lat1)*Math.cos(angularDistance) +
Math.cos(lat1)*Math.sin(angularDistance)*Math.cos(bearing) );
var lon2 = lon1 + Math.atan2(Math.sin(bearing)*Math.sin(angularDistance)*Math.cos(lat1),
Math.cos(angularDistance)-Math.sin(lat1)*Math.sin(lat2));
lat2 = lat2 * 180.0 / Math.PI;
lon2 = lon2 * 180.0 / Math.PI;
geom.appendCoordinate([lon2, lat2]);
}
return geom;
}
// Initalizes the map and starts up our timers to call various functions
function initialize_map() {
// Load stored map settings if present
@ -489,7 +513,9 @@ function initialize_map() {
distance *= 1.852;
}
var feature = new ol.Feature(new ol.geom.Circle(ol.proj.fromLonLat(SitePosition), distance));
var circle = make_geodesic_circle(SitePosition, distance, 360);
circle.transform('EPSG:4326', 'EPSG:3857');
var feature = new ol.Feature(circle);
feature.setStyle(circleStyle);
StaticFeatures.push(feature);
}