topic Re: how to retrieve a graphic that contains a drawing point in ArcGIS API for Silverlight Questions

how to retrieve a graphic that contains a drawing point

ThaoNguyen — Fri, 17 Dec 2010 18:22:44 GMT

My scenario:
- I have a drawing "point" icon for my map. When I click on a region in US, I want to highlight that region. I can get the highlight done. When clicking on a region, I don't want to run the query task again to get the region that contains the point. So, my design is I go thru the existing graphic list and find the region that "intersects" with that point, then do the highlight.
Something like this:

if (graphic.Geometry.Extent.Intersects(e.Geometry.Extent))
{
graphic.Select();
}

e is DrawEventArgs. graphic is from graphic layer on the map.

However, I got a problem that sometimes 2 regions contain that point and the result is both of them are selected. Please see the attached image, my clicking point is at the crossed symbol x. When I click at that point, both regions A and B are selected while I only want region B is selected.
Is there a way to fix this? Looks like to me graphic geometry is a rectangle and that causes the point to be inside both regions in the image?

I appreciate your help!

Re: how to retrieve a graphic that contains a drawing point

ThaoNguyen — Fri, 17 Dec 2010 18:32:14 GMT

My scenario:
- I have a drawing "point" icon for my map. When I click on a region in US, I want to highlight that region. I can get the highlight done. When clicking on a region, I don't want to run the query task again to get the region that contains the point. So, my design is I go thru the existing graphic list and find the region that "intersects" with that point, then do the highlight.
Something like this:

if (graphic.Geometry.Extent.Intersects(e.Geometry.Extent))
{
graphic.Select();
}

e is DrawEventArgs. graphic is from graphic layer on the map.

However, I got a problem that sometimes 2 regions contain that point and the result is both of them are selected. Please see the attached image, my clicking point is at the crossed symbol x. When I click at that point, both regions A and B are selected while I only want region B is selected.
Is there a way to fix this? Looks like to me graphic geometry is a rectangle and that causes the point to be inside both regions in the image?

I appreciate your help!

Attach the image.

Re: how to retrieve a graphic that contains a drawing point

JenniferNery — Sat, 11 Dec 2021 16:50:11 GMT

You can try this SDK sample http://help.arcgis.com/en/webapi/silverlight/samples/start.htm#SpatialQuery. It uses QueryTask based on the geometry (i.e. MapPoint if DrawMode is Point). You can modify this sample, you will not need a Draw object. You can obtain MapPoint through any of the mouse events.

  
System.Windows.Point screenPoint = args.GetPosition(MyMap);
ESRI.ArcGIS.Client.Geometry.MapPoint mapPoint = MyMap.ScreenToMap(screenPoint);

Re: how to retrieve a graphic that contains a drawing point

ThaoNguyen — Sat, 11 Dec 2021 16:50:13 GMT

You can try this SDK sample http://help.arcgis.com/en/webapi/silverlight/samples/start.htm#SpatialQuery. It uses QueryTask based on the geometry (i.e. MapPoint if DrawMode is Point). You can modify this sample, you will not need a Draw object. You can obtain MapPoint through any of the mouse events.
  
System.Windows.Point screenPoint = args.GetPosition(MyMap);
ESRI.ArcGIS.Client.Geometry.MapPoint mapPoint = MyMap.ScreenToMap(screenPoint);

Jennifer,
Like I said, I didn't want to run QueryTask again. I had looked at that spatial query before posting this question. I just want to use the exisitng graphics that I already query earlier and look for the one that contains the point. Looks like there is no way to get the right graphic WITHOUT running QueryTask?

Re: how to retrieve a graphic that contains a drawing point

JenniferNery — Mon, 20 Dec 2010 16:28:54 GMT

How about using FindGraphicsInHostCoordinates? You can look at the MouseClick event handler in this sample: http://help.arcgis.com/en/webapi/silverlight/samples/start.htm#InfoWindowSimple

Re: how to retrieve a graphic that contains a drawing point

AliMirzabeigi — Sat, 11 Dec 2021 16:50:16 GMT

You can do the following in the MouseClick event of your Map control to get the graphics that intersect your MapPoint.

Assumptions in the code snippet:
- MyMap: The Map control in your application
- MyFeatureLayer: The FeatureLayer in your map you are intersecting the map point
- MyGraphicsLayer: The layer to show the intersecting result(s)

FeatureLayer featureLayer = MyMap.Layers["MyFeatureLayer"] asFeatureLayer;
 
System.Windows.Point screenPnt = MyMap.MapToScreen(e.MapPoint);
GeneralTransform generalTransform = MyMap.TransformToVisual(Application.Current.RootVisual);
System.Windows.Point transformScreenPnt = generalTransform.Transform(screenPnt);
IEnumerable<Graphic> results = featureLayer.FindGraphicsInHostCoordinates(transformScreenPnt);

GraphicsLayer graphicsLayer = MyMap.Layers["MyGraphicsLayer"] asGraphicsLayer;

foreach (Graphic graphic in results)
{
Graphic g = newGraphic() { Geometry = graphic.Geometry };
graphicsLayer.Graphics.Add(g);
}

Re: how to retrieve a graphic that contains a drawing point

ThaoNguyen — Sat, 11 Dec 2021 16:50:19 GMT

You can do the following in the MouseClick event of your Map control to get the graphics that intersect your MapPoint.

Assumptions in the code snippet:
- MyMap: The Map control in your application
- MyFeatureLayer: The FeatureLayer in your map you are intersecting the map point
- MyGraphicsLayer: The layer to show the intersecting result(s)
FeatureLayer featureLayer = MyMap.Layers["MyFeatureLayer"] asFeatureLayer;
 
System.Windows.Point screenPnt = MyMap.MapToScreen(e.MapPoint);
GeneralTransform generalTransform = MyMap.TransformToVisual(Application.Current.RootVisual);
System.Windows.Point transformScreenPnt = generalTransform.Transform(screenPnt);
IEnumerable<Graphic> results = featureLayer.FindGraphicsInHostCoordinates(transformScreenPnt);

GraphicsLayer graphicsLayer = MyMap.Layers["MyGraphicsLayer"] asGraphicsLayer;

foreach (Graphic graphic in results)
{
Graphic g = newGraphic() { Geometry = graphic.Geometry };
graphicsLayer.Graphics.Add(g);
}

Thanks Jennifer and Ali! Looks like that can resolve my problem, but I cannot test it because I cannot find the property RootVisual from Application.Current. I tried Application.Current.MainWindow but that is null.

Re: how to retrieve a graphic that contains a drawing point

JenniferNery — Sun, 12 Dec 2021 16:22:50 GMT

If you are using WPF:

GeneralTransform generalTransform = MyMap.TransformToVisual(Application.Current.MainWindow);
System.Windows.Point transformScreenPnt = generalTransform.Transform(screenPnt);

IEnumerable<Graphic> selected =
                parcelGraphicsLayer.FindGraphicsInHostCoordinates(transformScreenPnt);

Re: how to retrieve a graphic that contains a drawing point

ThaoNguyen — Sat, 11 Dec 2021 16:50:22 GMT

If you are using WPF:

GeneralTransform generalTransform = MyMap.TransformToVisual(Application.Current.MainWindow);
System.Windows.Point transformScreenPnt = generalTransform.Transform(screenPnt);

IEnumerable<Graphic> selected =
                parcelGraphicsLayer.FindGraphicsInHostCoordinates(transformScreenPnt);

I used MainWindow, but it always returned me null.

Re: how to retrieve a graphic that contains a drawing point

ThaoNguyen — Wed, 22 Dec 2010 11:51:19 GMT

I used MainWindow, but it always returned me null.

I found out why it is always null for my case.

Another question. My xaml has something like this:
<UserControl>
<UserControl.Resources/>
<Grid>my map is in here</Grid>
</UserControl>

Is that true that the MainWindow would be the Grid element in my xaml?

Re: how to retrieve a graphic that contains a drawing point

DominiqueBroux — Thu, 23 Dec 2010 12:37:32 GMT

The main window won't be the grid inside your control. It could be the control itself if it's used as main window.

Re: how to retrieve a graphic that contains a drawing point

ThaoNguyen — Sat, 11 Dec 2021 16:50:24 GMT

You can do the following in the MouseClick event of your Map control to get the graphics that intersect your MapPoint.

Assumptions in the code snippet:
- MyMap: The Map control in your application
- MyFeatureLayer: The FeatureLayer in your map you are intersecting the map point
- MyGraphicsLayer: The layer to show the intersecting result(s)
FeatureLayer featureLayer = MyMap.Layers["MyFeatureLayer"] asFeatureLayer;
 
System.Windows.Point screenPnt = MyMap.MapToScreen(e.MapPoint);
GeneralTransform generalTransform = MyMap.TransformToVisual(Application.Current.RootVisual);
System.Windows.Point transformScreenPnt = generalTransform.Transform(screenPnt);
IEnumerable<Graphic> results = featureLayer.FindGraphicsInHostCoordinates(transformScreenPnt);

GraphicsLayer graphicsLayer = MyMap.Layers["MyGraphicsLayer"] asGraphicsLayer;

foreach (Graphic graphic in results)
{
Graphic g = newGraphic() { Geometry = graphic.Geometry };
graphicsLayer.Graphics.Add(g);
}

I'm just back to this. I don't have e.MapPoint but having DrawEventArgs e which can give me Geometry. How do I create a MapPoint or Point using Geometry?

I tried the following but looks like it's not correct because FindGraphicsInHostCoordinates() does not return me graphics sometimes. I'm using this method from graphic layer, not feature layer.

System.Windows.Point screenPnt = MainMap.MapToScreen(new MapPoint(e.Geometry.Extent.XMax,e.Geometry.Extent.YMax));

Thanks!

Re: how to retrieve a graphic that contains a drawing point

JenniferNery — Sat, 11 Dec 2021 16:50:27 GMT

You can use Intersects() method http://help.arcgis.com/en/webapi/silverlight/apiref/ESRI.ArcGIS.Client~ESRI.ArcGIS.Client.Geometry.Envelope~Intersects.html

Something like this, where args.Geometry is the MapPoint created by Draw. This code-snippet allows me to select all graphics that contain the MapPoint.

foreach (var g in graphicsLayer.Graphics)
{
 if (g.Geometry.Extent.Intersects(args.Geometry.Extent))
  g.Selected = true;
}

Re: how to retrieve a graphic that contains a drawing point

ThaoNguyen — Sat, 11 Dec 2021 16:50:30 GMT

You can use Intersects() method http://help.arcgis.com/en/webapi/silverlight/apiref/ESRI.ArcGIS.Client~ESRI.ArcGIS.Client.Geometry.Envelope~Intersects.html

Something like this, where args.Geometry is the MapPoint created by Draw. This code-snippet allows me to select all graphics that contain the MapPoint.
foreach (var g in graphicsLayer.Graphics)
{
 if (g.Geometry.Extent.Intersects(args.Geometry.Extent))
  g.Selected = true;
}

That is what I'm doing and it is why I posted this question. I had what you had above in my first post in this thread. It does NOT give the right result as stated in my first post :).

Re: how to retrieve a graphic that contains a drawing point

JenniferNery — Tue, 01 Mar 2011 15:50:50 GMT

Oh, could you verify that the geometries have the same SpatialReference as the MapPoint? If they are found to be not equal, Intersects() will return false.

Re: how to retrieve a graphic that contains a drawing point

ThaoNguyen — Wed, 02 Mar 2011 14:15:19 GMT

Oh, could you verify that the geometries have the same SpatialReference as the MapPoint? If they are found to be not equal, Intersects() will return false.

Yes, they have the same SpatialReference. It's just that the result returned is more than what I draw. You can look at the image I attached in the 2nd post. Intersects() won't work in all cases.