# virtual earth: drawing a radius

| Commentsas i continue to build on top of my virtual earth example that uses proximity searching, i found myself wanting to add more visualization to the mix. i wanted the radius being searched to actually show a radius ring for the area...so the user could see the proximity being searched where the results are plotted.

so, i started digging -- how do you draw a circle using the polyline api? hmmm...rounded corners with straight lines...seemed like a challenge.

well after a prod to some people i was pointed to a solution already doing this!

and thus the ViaVE Wiki had the answer. basically it is a javascript function like this:

1: function addCircle(polyname, latin, lonin, radius, vecolor, linewidth)

` 2: { `

3: var locs = new Array();

4: var lat1 = latin * Math.PI/180.0;

5: var lon1 = lonin * Math.PI/180.0;

6: var d = radius/3956;

7: var x;

8: for (x = 0; x <= 360; x++)

` 9: { `

10: var tc = (x / 90)* Math.PI / 2;

11: var lat = Math.asin(Math.sin(lat1)*Math.cos(d)+Math.cos(lat1)*Math.sin(d)*Math.cos(tc));

` 12: lat = 180.0 * lat / Math.PI; `

13: var lon;

14: if (Math.cos(lat1)==0)

` 15: { `

16: lon=lonin; // endpoint a pole

` 17: } `

18: else

` 19: { `

` 20: lon = ((lon1 - Math.asin(Math.sin(tc) * Math.sin(d)/Math.cos(lat1)) + Math.PI) % (2 * Math.PI)) - Math.PI; `

` 21: } `

` 22: lon = 180.0 * lon / Math.PI; `

23: var loc = new VELatLong(lat,lon);

` 24: locs.push(loc); `

` 25: } `

26: var poly = new VEPolyline(polyname, locs, vecolor , linewidth);

27: return poly;

` 28: }`

(note: the 3956 indicates this is miles...if you need km, then you'd have to adjust the earth radius setting to be km instead)

now that i add that to my code, i simply call:

1: map.AddPolyline(addCircle("SearchRadius", center.Latitude, center.Longitude, $get("MilesRadius").value, new VEColor(255,0,0,1), 4));

and have a radius drawn around my resulted plot points.

the beauty is that as with everything, this applies to the 3d views as well:

very cool -- hope this helps others as well.