Overiding

Question

This is semi-related to this thread:

How is ClusterGraphicsAsync suposed to be overridden? I have overridden OnCreateGraphic, but I'm a bit confused on overriding ClusterGraphicsAsync. From the API reference:The clustering algorithm is expected to run on a seperate cancellable thread to prevent blocking the UI. On completion, raise ClusteringCompleted by invoking OnClusteringCompleted. The event should not be raised if clustering was cancelled.

I'm also guessing that ClusterGraphicsAsync calls OnCreateGraphic?, but in that case what does it do with the returned graphics?

So my questions are:
1) How do I  run on a seperate cancellable thread to prevent blocking the UI

?

2) How do   raise ClusteringCompleted by invoking OnClusteringCompleted

?

3) How does CancelAsync factor into all of this? Much they also be overridden, if so how?

4a) Does ClusterGraphicsAsync call OnCreateGraphic?

4b) If so, what do you do with the returning graphics?

4c) If you create clusters from the "graphics" parameters based on the "resolution" parameter, is there a smart way of doing this, as this seems like it can be very complicated and easily could be O(n^2)?

ANY thoughts are welcome

PhilipKnight1 · Answer

Hi Phil,
Thanks for sharing the code, it was indeed very helpful :) !!
I got my code working to a point where I can cluster according to an attribute of the graphic.
The problem I  am facing however is that I am not able to control the Zoom level.

I tried to play with the range property (Increasing the range) and that helps but I am not sure this is the right way to do it.
Can you help me on this.
I am trying to give user different views of data at different Zoom levels using cluster.
So at minimum Zoom and  -> On block appears (which clusters all the graphics of same type).
In between -> I want the block to appear (only the information I am displaying on the block increases)
Maximum Zoom I want to make visible all the graphics.

It's been a little while since I have worked with the API, but there is an event that gets fired when the zoom level changes (I'm sure you can find info on it in the forums somewhere), add an event listener to this event and then depending on the zoom level, configure how you want the cluster to work.

Keep in mind that there is no turn on/off clusterer, you either set the clusterer or you don't set it at all or set it to null. Goodluck!

AnkitaBhatia · Answer

Hi Phil,
Thanks for sharing the code, it was indeed very helpful :) !!
I got my code working to a point where I can cluster according to an attribute of the graphic.
The problem I  am facing however is that I am not able to control the Zoom level.

I tried to play with the range property (Increasing the range) and that helps but I am not sure this is the right way to do it.
Can you help me on this.
I am trying to give user different views of data at different Zoom levels using cluster.
So at minimum Zoom and  -> On block appears (which clusters all the graphics of same type).
In between -> I want the block to appear (only the information I am displaying on the block increases)
Maximum Zoom I want to make visible all the graphics.

PhilipKnight1 · Answer

So it surely wasn't easy. In fact I never did get everything to work, but I did learn some things and perhaps others will be able to build upon this: My original reason for doing this original was that I didn't know what graphic I wanted to remove from being clustered until I saw what graphics were left over after clustering (by left-over I mean not clustered). I was able to cluster the graphics, but I wasn't able to do it properly. Clusters were far too close together and just sitting on top of eachother, or else they were just all gobbled together. But it also seemed that some graphics were just not getting grouped together. public override void ClusterGraphicsAsync(IEnumerable graphics, double resolution) { int incomingTotal = graphics.Count(); int total = 0; //TODO run on seperate cancellable thread //BackgroundWorkers or Tasks executed on the thread pool are possible options. //if (bw.IsBusy != true) //{ // bw.RunWorkerAsync(); //} //else //{ //} GraphicCollection returnGraphics = new GraphicCollection(); //Group graphics into collections that will be turned into clusters IEnumerable graphicGroups = groupGraphics(graphics, resolution); GraphicCollection gCollection; for (int i = 0; i < graphicGroups.Count(); i++ ) { gCollection = graphicGroups.ElementAt(i); if (gCollection.Count > 2) { Utility.removeTextSymbols(ref gCollection); //need to remove TextSymbols or else they will be counted MapPoint mp = getCenter(gCollection); Graphic cluster = OnCreateGraphic2(gCollection, mp, gCollection.Count); returnGraphics.Add(cluster); total += gCollection.Count; } else //should just add one TextSymbol and one GraphicSymbol { foreach (Graphic g in gCollection) { returnGraphics.Add(g); } total += 1; } } //raise ClusteringCompleted by invoking OnClusteringCompleted OnClusteringCompleted(returnGraphics); } private IEnumerable groupGraphics(IEnumerable graphics, double resolution) { Queue q = new Queue(graphics); Collection clusters = new Collection(); int totalCount = 0; double range = resolution * 50; while (q.Count > 0) { Graphic g = q.Dequeue(); GraphicCollection gCollection = new GraphicCollection(); Envelope searchEnvelope = g.Geometry.Extent; //expand the evelope to include the search resolution searchEnvelope.XMax += (60*resolution); searchEnvelope.YMax += (60*resolution); searchEnvelope.XMin -= (60*resolution); searchEnvelope.YMin -= (60*resolution); gCollection.Add(g); //iterate through q, finding all graphics within extent if (q.Count > 0) { Graphic searchG = null; Graphic firstSearchG = null; Graphic prevSearchG = null; //remove graphics from queue that are within searchEvelope while (q.Count > 0 && (searchG == null || searchG != firstSearchG || prevSearchG == null)) { prevSearchG = searchG; searchG = q.Dequeue(); //new search graphic if (firstSearchG == null) { firstSearchG = searchG; } //if (searchEnvelope.Intersects(searchG.Geometry.Extent) == true) //if (envelopesIntersect(searchEnvelope, searchG.Geometry.Extent) == true) if (withinRange(g, searchG, range) == true) { if (searchG.Symbol.GetType() == typeof(ESRI.ArcGIS.Client.FeatureService.Symbols.PictureMarkerSymbol)) { gCollection.Insert(0,searchG); } else { gCollection.Add(searchG); //send textsymbol to end of colelction, so drawn last } totalCount++; if (searchG == firstSearchG) { firstSearchG = null; } } else { q.Enqueue(searchG); } } } clusters.Add(gCollection); } return clusters; } private bool withinRange(Graphic g1, Graphic g2, double range) { double a = g2.Geometry.Extent.YMax - g1.Geometry.Extent.YMax; double b = g2.Geometry.Extent.XMax - g1.Geometry.Extent.XMax; double c = Math.Sqrt(Math.Pow(a, 2) + Math.Pow(b, 2)); if (c <= range) { return true; } return false; }