topic Re: Adding Circle to Map with radius in metres in ArcGIS API for Silverlight Questions

Adding Circle to Map with radius in metres

KobusPelser — Wed, 28 Apr 2010 10:05:23 GMT

I need to add a circle to the map with a radius in metres. How can I go about this?

Adding Circle to Map with radius in metres

DominiqueBroux — Wed, 28 Apr 2010 13:32:07 GMT

What is the spatial reference of your map?

Re: Adding Circle to Map with radius in metres

AlexAgranov — Mon, 11 Oct 2010 18:18:28 GMT

What is the spatial reference of your map?

Could you explain what you mean by that? I also need to draw a circle with a Graphic serving as the vertex.

Re: Adding Circle to Map with radius in metres

dotMorten_esri — Mon, 11 Oct 2010 18:57:31 GMT

What does Map.SpatialReference.WKID return after the map has loaded?

This sample app has a radius measure tool that works if your map is in geographic coordinates:
http://resources.esri.com/arcgisserver/apis/silverlight/index.cfm?fa=codeGalleryDetails&scriptID=16504

Re: Adding Circle to Map with radius in metres

AlexAgranov — Tue, 12 Oct 2010 18:20:11 GMT

What does Map.SpatialReference.WKID return after the map has loaded?

This sample app has a radius measure tool that works if your map is in geographic coordinates:
http://resources.esri.com/arcgisserver/apis/silverlight/index.cfm?fa=codeGalleryDetails&scriptID=16504

Basically the Geodesic.GetPointFromHeading() calculates points that are based on the earths' curvature, so I end up with an ellipse. In close distances, like a mile I don't really care about that and just want points that give me a circle.

Re: Adding Circle to Map with radius in metres

dotMorten_esri — Wed, 13 Oct 2010 22:08:44 GMT

All you have to do is simplify the code to not take the curvature into account. That's just a little simple Cosine/Sine calculation.

Re: Adding Circle to Map with radius in metres

wangzhifang — Sat, 11 Dec 2021 20:12:53 GMT

/// <summary>
        /// create a new circle geometry, which is polygon, depending on the given center and radius
        /// @diligentpig
        /// @http://newnaw.com
        /// </summary>
        /// <param name="ptCenter">center of the newly created circle.</param>
        /// <param name="dRadius">radius of the newly created circle, in screen pixel.</param>
        /// <param name="n">precision, represents how many point does the return polygon have. These points are symmetrily located.
        /// if n=0, then transfer to default precision which n=32</param>
        /// <param name="map">the map control, used for converting mappoint to screenpoint and vice versa.</param>
        /// <returns>a polygon geometry simulate a circle</returns>
        public static Polygon createCirclePolygon(MapPoint ptCenter, double dRadius, int n,ESRI.ArcGIS.Client.Map map)
        {
            PointCollection pc = new PointCollection();
            System.Windows.Point ptCenterScreen = map.MapToScreen(ptCenter);
            n = n <= 0 ? 32 : n;
            for (int i = 0; i < n; i++)
            {
                //ecah point on the circle, counterclockwise
                double angle = (Math.PI * 2) / n * i;
                System.Windows.Point p = new System.Windows.Point()
                {
                    X = ptCenterScreen.X + dRadius * Math.Cos(angle),
                    Y = ptCenterScreen.Y + dRadius * Math.Sin(angle)
                };
                pc.Add(map.ScreenToMap(p));
            };
            //add the last, which is exact the first, point.
            pc.Add(map.ScreenToMap(new System.Windows.Point()
            {
                X=ptCenterScreen.X+dRadius,
                Y=ptCenterScreen.Y
            }));

            Polygon polyg = new Polygon()
            {
                SpatialReference=map.SpatialReference
            };
            polyg.Rings.Add(pc);

            return polyg;
        }