Drawing circle of 3 km radius in ArcGIS API for JavaScript?

Question

I am able to draw the circle but I want a circle of radius 3 kms

I have checked all the previous posts.

I want to know what is the units of radius in the below code.

var radius, circle, ring, pts, angle;
var currentPoint = new esri.geometry.Point(longitude, latitude, this.parent.esriMap.spatialReference);
currentPoint = esri.geometry.geographicToWebMercator(currentPoint);
circle = new esri.geometry.Polygon(this.parent.esriMap.spatialReference);
ring = []; // point that make up the circle 
pts = 40; // number of points on the circle 
angle = 360 / pts; // used to compute points on the circle 
for (var i = 0; i <= 360; i = i + 10) {
 var radian = i * (Math.PI / 180.0);
 var x1= radius * Math.cos(radian);
 var y1= radius * Math.sin(radian);
 var circlePoint = new esri.geometry.Point(x1, y1, this.parent.esriMap.spatialReference);
 circlePoint = esri.geometry.geographicToWebMercator(circlePoint);
 points[i] = new esri.geometry.Point(
 parseFloat(circlePoint.x) + parseFloat(currentPoint.x), parseFloat(circlePoint.y) + parseFloat(currentPoint.y),
 this.parent.esriMap.spatialReference);
 ring.push(points[i]);
}
circle.addRing(ring);
//rest code to add the layers to map

Answer 1

Creating a 3km radius circle is quite easy in ArcGIS Desktop:

1. Create a point featureclass marking the center of your area of interest.
2. Use the Buffer (Analysis) tool to create the 3km radius buffer around the point featureclass.

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enter image description here

Answer 2

When solving it programmatically I would start with this Snippet from ESRI:

Create Graphic Buffers around Selected Features Snippet:

///<summary>Draws graphic buffers around the selected features in the map using distance units specified.</summary>
///
///<param name="activeView">An IActiveView interface.</param>
///<param name="distance">A System.Double that is the distance in map units around the select features to draw a graphic buffer. Example: 10</param>
/// 
///<remarks></remarks>
public void CreateGraphicBuffersAroundSelectedFeatures(ESRI.ArcGIS.Carto.IActiveView activeView, System.Double distance)
{
 //parameter check
 if (activeView == null || distance < 0)
 {
 return;
 }
 ESRI.ArcGIS.Carto.IMap map = activeView.FocusMap;
 // Clear any previous buffers from the screen
 ESRI.ArcGIS.Carto.IGraphicsContainer graphicsContainer = (ESRI.ArcGIS.Carto.IGraphicsContainer)map; // Explicit Cast
 graphicsContainer.DeleteAllElements();
 // Verify there is a feature(s) selected
 if (map.SelectionCount == 0)
 {
 return;
 }
 // Reset to the first selected feature
 ESRI.ArcGIS.Geodatabase.IEnumFeature enumFeature = (ESRI.ArcGIS.Geodatabase.IEnumFeature)map.FeatureSelection; // Explicit Cast
 enumFeature.Reset();
 ESRI.ArcGIS.Geodatabase.IFeature feature = enumFeature.Next();
 // Buffer all the selected features by the buffer distance and create a new polygon element from each result
 ESRI.ArcGIS.Geometry.ITopologicalOperator topologicalOperator;
 ESRI.ArcGIS.Carto.IElement element;
 while (!(feature == null))
 {
 topologicalOperator = (ESRI.ArcGIS.Geometry.ITopologicalOperator)feature.Shape; // Explicit Cast
 element = new ESRI.ArcGIS.Carto.PolygonElementClass();
 element.Geometry = topologicalOperator.Buffer(distance);
 graphicsContainer.AddElement(element, 0);
 feature = enumFeature.Next();
 }
 activeView.PartialRefresh(ESRI.ArcGIS.Carto.esriViewDrawPhase.esriViewGraphics, null, null);
}

available at: http://help.arcgis.com/en/sdk/10.0/arcobjects_net/componenthelp/index.html#//0049000000n3000000

this takes a feature point geometry as input but you could create your own geometry with the coordinates of the buffer you want to draw. The distance is in map units but following site might help you get the relation to the geographic distance:

ArcGis Desktop Help: About setting distance units

http://webhelp.esri.com/arcgisdesktop/9.3/index.cfm?TopicName=About_setting_distance_units