Displaying a circular arc with the Graphic Tracker

ManfredLauterbach

Hi,

This documentation : http://help.arcgis.com/en/sdk/10.0/arcobjects_net/conceptualhelp/index.html#/Using_a_GraphicTracker/0001000004tv000000/ provides some information about the graphic tracker.
It states that the tracker only supports IPoint, IPolyline, and IPolygon geometry.

Thanks to Neil's explanation (http://forums.arcgis.com/threads/54068-Extracting-elliptical-properties-from-TrackCircle%28%29-geometry) I understand how a polygon is several objects at once - it could represent a circular arc.
In other words, we are able to create a circular arc (which could be a complete circle), and add it to the graphics tracker - but I'm having trouble with this - nothing is displayed, even though the call to add the graphic succeeds :

           ISimpleFillSymbol fillSymbol = new SimpleFillSymbolClass();           RgbColorClass red = new RgbColorClass() { Red = 255, Green = 0, Blue = 0 };           fillSymbol.Color = red;           fillSymbol.Style = esriSimpleFillStyle.esriSFSSolid;           IGraphicTrackerSymbol graphicTrackerSymbol = graphicTracker.CreateSymbol(fillSymbol as ISymbol, null);            PointClass centroid = new PointClass();           PointClass fromPoint = new PointClass();           PointClass toPoint = new PointClass();           centroid.PutCoords(0, 0);           fromPoint.PutCoords(0, 10);           toPoint.PutCoords(10, 0);           CircularArcClass circularArc = new CircularArcClass();           circularArc.PutCoords(centroid, fromPoint, toPoint, esriArcOrientation.esriArcClockwise);            int graphicID = graphicTracker.Add(circularArc, graphicTrackerSymbol);            mapControl.Refresh(); 

However, when displaying something else, like a character marker symbol, it displays correctly :

           ICharacterMarkerSymbol charSymbol = new CharacterMarkerSymbolClass();           charSymbol.CharacterIndex = 122;           charSymbol.Color = new RgbColorClass() { Red = 15, Green = 255, Blue = 255 };           charSymbol.Font = tactFont;           charSymbol.Size = 36;           charSymbol.XOffset = 0;           charSymbol.YOffset = 0;            PointClass offset = new PointClass() { X = 0, Y = 0 };           IGraphicTrackerSymbol graphicTrackerSymbol = graphicTracker.CreateSymbol(charSymbol as ISymbol, null);           int graphicID = graphicTracker.Add(offset, graphicTrackerSymbol); 

Does the tracker only display objects that do not have an associated geometry (i.e. the graphics tracker accepts a separate geometry object only to position the symbol)?
I've found several references on the web which indicate that the first section of code (with the circular arc) should be working - can anyone explain what is wrong there?


(similarly with Cartographic Symbol - nothing is displayed) :

           CartographicLineSymbolClass cartoSymbol = new CartographicLineSymbolClass();           cartoSymbol.Color = new RgbColorClass() { Red = 0, Green = 0, Blue = 255 };           cartoSymbol.Cap = esriLineCapStyle.esriLCSButt;           cartoSymbol.Join = esriLineJoinStyle.esriLJSBevel;           cartoSymbol.Width = 2;            PointClass p1 = new PointClass() {X = 0, Y = 10};           PointClass p2 = new PointClass() {X = 10, Y = 0};           ILine line = new LineClass();           line.PutCoords(p1, p2);            IEnvelope env = new EnvelopeClass() { XMin = -10, XMax = 10, YMin = -10, YMax = 10 };           IGraphicTrackerSymbol graphicTrackerSymbol = graphicTracker.CreateSymbol(cartoSymbol as ISymbol, null);           int graphicID = graphicTracker.Add(env, graphicTrackerSymbol); 

NeilClemmons_GISinc

I've never used this class but from the documentation it looks like the graphics tracker only works on high level geometries.  Even though there are many classes that implement IGeometry only those that also implement IPoint, IMultiPoint, IPolyline, or IPolygon are considered high level geometries (at least in the 2d world).  So, what you need to do is create a polyline from the circular arc.  To do this, you create a new polyline object and add the circular arc to its segment collection.  You then pass the polyline to the graphics tracker.

Dim polyline As IPolyline = New Polyline
DirectCast(polyline, ISegmentCollection).AddSegment(circularArc)

This is why your example with the point worked and the other two didn't.  A Point is a high level geometry while the circular arc and envelope are not.