topic Re: Area And Perimeter in ArcGIS API for Silverlight Questions

Area And Perimeter

NathalieNeagle — Sat, 09 Oct 2010 17:31:21 GMT

I'm using this example and it works great in the example with projection 102100 but I'm using projection 4326 WGS 1984 esridecimaldegrees and my numbers are way off can someone tell what I need to change
buthttp://help.arcgis.com/en/webapi/silverlight/samples/start.htm#AreasAndLengths

I think it is here but not sure

   private void GeometryService_AreasAndLengthsCompleted(object sender, AreasAndLengthsEventArgs args)
        {
            //TODO: Geometry service not returning correct values, area unit seems invalid, may need to use data in 
            //planar coordinate space

            // convert results from meters into miles and sq meters into sq miles for our display
            double miles = args.Results.Lengths[0] * 0.0006213700922;
            double sqmi = Math.Abs(args.Results.Areas[0]) * 0.0000003861003;
            ResponseTextBlock.Text = String.Format("Polygon area: {0} sq. miles\nPolygon perimeter: {1} miles.", Math.Round(sqmi, 3), Math.Round(miles, 3));
        }

Re: Area And Perimeter

NathalieNeagle — Sun, 10 Oct 2010 03:18:13 GMT

I'm still in need of the question I posted eailer but no I ran into another problem so I was hoping if someone was kind enough to answer one maybe they have the knowledge to do both.

So I've implemented the "area and perimeter" (http://help.arcgis.com/en/webapi/silverlight/2.1/samples/start.htm#AreasAndLengths) and the "Line Length" (http://help.arcgis.com/en/webapi/silverlight/2.1/samples/start.htm#Lengths)
I've add a button to clear the graphics and switch back and fourth between the two but I can't seem to figure out how to get out of them. I mean what do I need to call to get back to the normal mouse clicks....so the left mouse click stops drawing line or polys and can pan or zoom (like the default mouse actions.).....

Thanks

Re: Area And Perimeter

NathalieNeagle — Sun, 10 Oct 2010 03:24:21 GMT

I'm still in need of the question I posted eailer but no I ran into another problem so I was hoping if someone was kind enough to answer one maybe they have the knowledge to do both.

So I've implemented the "area and perimeter" (http://help.arcgis.com/en/webapi/silverlight/2.1/samples/start.htm#AreasAndLengths) and the "Line Length" (http://help.arcgis.com/en/webapi/silverlight/2.1/samples/start.htm#Lengths)
I've add a button to clear the graphics and switch back and fourth between the two but I can't seem to figure out how to get out of them. I mean what do I need to call to get back to the normal mouse clicks....so the left mouse click stops drawing line or polys and can pan or zoom (like the default mouse actions.).....

Thanks

I just figured this out a second after I posted this question. All I did was

 MyDrawObject.IsEnabled = false;

I'm still hoping someone can help me out with polygon area mis-calculations.

Thanks
NN

Re: Area And Perimeter

NathalieNeagle — Sat, 11 Dec 2021 10:59:05 GMT

   private void GeometryService_AreasAndLengthsCompleted(object sender, AreasAndLengthsEventArgs args)
        {
            //TODO: Geometry service not returning correct values, area unit seems invalid, may need to use data in 
            //planar coordinate space

            // convert results from meters into miles and sq meters into sq miles for our display
            double miles = args.Results.Lengths[0] * 0.0006213700922;
            double sqmi = Math.Abs(args.Results.Areas[0]) * 0.0000003861003;
            ResponseTextBlock.Text = String.Format("Polygon area: {0} sq. miles\nPolygon perimeter: {1} miles.", Math.Round(sqmi, 3), Math.Round(miles, 3));
        }

It seems like the perimeter area code is converting from meters to miles and sq miles and I need to convert decimal degrees to miles and sq miles. I tried to change the caluclation but it doesn't work

double miles = args.Results.Lengths[0] * 0.0006213700922;
double sqmi = Math.Abs(args.Results.Areas[0]) * 0.0000003861003;

Has anyone ran into this problem and solved it. I would be super greatful.

Thanks
Nathalie

Re: Area And Perimeter

ChristineZeller — Tue, 12 Oct 2010 15:14:40 GMT

I'm having the same issue as Nathalie and I'm stuck.
I've also implemented the Area and Perimeter tool and I�??m also using the WGS 1984 projection (spatial ref 4326, units esriDecimalDegrees). Can someone help Nathalie and me out and let us know what to change to calculate a somewhat accurate area and line lengths
http://help.arcgis.com/en/webapi/silverlight/samples/start.htm#AreasAndLengths

Thanks
Christine

Re: Area And Perimeter

ChristopherHill — Tue, 12 Oct 2010 18:22:11 GMT

Hello,

When you are calling the GeometryService.AreaAndLengthsAsync() method are you passing the units of measurement you want returned? The unit of measurement is defined using a Enumeration of type LinearUnit. there are parameters for length unit and area unit that you can pass to the function. if you do not pass any paramters the area and lengths will return in units of Spatial Reference (in your case degrees)

example:

GeometryService.AreaAndLengthsAsync(myGraphics,LinearUnit.Meters,LinearUnit.Meters,null);

so if you are just calling GeometryService.AreaAndLengthsAsync(myGraphics) you are going to get area and lengths in degrees.

AreaAndLengthsAsync(IList<Graphic> graphics,LinearUnit lengthUnit,LinearUnit areaUnit, object userToken)
http://help.arcgis.com/en/webapi/silverlight/apiref/ESRI.ArcGIS.Client~ESRI.ArcGIS.Client.Tasks.GeometryService~AreasAndLengthsAsync(IList%601,Nullable%601,Nullable%601,Object).html

LinearUnit Enum
http://help.arcgis.com/en/webapi/silverlight/apiref/ESRI.ArcGIS.Client~ESRI.ArcGIS.Client.Tasks.LinearUnit.html

Re: Area And Perimeter

NathalieNeagle — Sat, 11 Dec 2021 10:59:08 GMT

Hey Chris,

Thanks for your post so I'm think I'm really close. I'm still getting really small numbers so I'm not sure if I'm missing something.

Here's what i'm doing.



        private void MyDrawObject_DrawComplete(object sender, DrawEventArgs args)
        {
            ESRI.ArcGIS.Client.Geometry.Polygon polygon = args.Geometry as ESRI.ArcGIS.Client.Geometry.Polygon;
            polygon.SpatialReference = MyMap.SpatialReference;
            Graphic graphic = new Graphic()
            {
                Symbol = LayoutRoot.Resources["DefaultFillSymbol"] as ESRI.ArcGIS.Client.Symbols.Symbol,
                Geometry = polygon,
            };

            GeometryService geometryService =
                new GeometryService("http://sampleserver3.arcgisonline.com/ArcGIS/rest/services/Geometry/GeometryServer");
            geometryService.AreasAndLengthsCompleted += GeometryService_AreasAndLengthsCompleted;
            geometryService.Failed += GeometryService_Failed;

            GraphicsLayer graphicsLayer = MyMap.Layers["MyGraphicsLayer"] as GraphicsLayer;
            graphicsLayer.Graphics.Add(graphic);

            List<Graphic> graphicList = new List<Graphic>();
            graphicList.Add(graphic);

 geometryService.AreasAndLengthsAsync(graphicList, LinearUnit.SurveyMile, LinearUnit.SurveyMile, null);

        }





        private void GeometryService_AreasAndLengthsCompleted(object sender, AreasAndLengthsEventArgs args)
           {

       ResponseTextBlock.Text = String.Format("Polygon area: {0} sq. miles\nPolygon perimeter: {1} miles.", Math.Round(args.Results.Areas[0], 3), Math.Round(args.Results.Lengths[0], 3));
        }

Nathalie

Re: Area And Perimeter

ChristineZeller — Sat, 11 Dec 2021 10:59:11 GMT

Yea I'm still getting a really small number. I tried it slightly different than Nathalie but sounds like the same results. Do you know what I am missing.


 private void MyDrawObject_DrawComplete(object sender, DrawEventArgs args)
        {
            ESRI.ArcGIS.Client.Geometry.Polygon polygon = args.Geometry as ESRI.ArcGIS.Client.Geometry.Polygon;
            polygon.SpatialReference = MyMap.SpatialReference;
            Graphic graphic = new Graphic()
            {
                Symbol = LayoutRoot.Resources["DefaultFillSymbol"] as ESRI.ArcGIS.Client.Symbols.Symbol,
                Geometry = polygon,
            };

            GeometryService geometryService =
                new GeometryService("http://sampleserver3.arcgisonline.com/ArcGIS/rest/services/Geometry/GeometryServer");
            geometryService.AreasAndLengthsCompleted += GeometryService_AreasAndLengthsCompleted;
            geometryService.Failed += GeometryService_Failed;

            GraphicsLayer graphicsLayer = MyMap.Layers["MyGraphicsLayer"] as GraphicsLayer;
            graphicsLayer.Graphics.Add(graphic);

            List<Graphic> graphicList = new List<Graphic>();
            graphicList.Add(graphic);


           



            geometryService.AreasAndLengthsAsync(graphicList,LinearUnit.Meter, LinearUnit.Meter, null);

          

                 
                   }

        private void GeometryService_AreasAndLengthsCompleted(object sender, AreasAndLengthsEventArgs args)

        {
            //TODO: Geometry service not returning correct values, area unit seems invalid, may need to use data in 
            //planar coordinate space

               // convert results from meters into miles and sq meters into sq miles for our display
            double miles = args.Results.Lengths[0] * 0.0006213700922;
            double sqmi = Math.Abs(args.Results.Areas[0]) * 0.0000003861003;
            ResponseTextBlock.Text = String.Format("Polygon area: {0} sq. miles\nPolygon perimeter: {1} miles.", Math.Round(sqmi, 3), Math.Round(miles, 3));

 
        }

Re: Area And Perimeter

NathalieNeagle — Wed, 13 Oct 2010 22:08:45 GMT

Christine,
Did you make any more progress. I'm still stuck.
Nathalie

Re: Area And Perimeter

ChristopherHill — Wed, 13 Oct 2010 22:22:02 GMT

Hi,

Both code samples are correct. Let me ask a few questions to pin point the problem you are both having.

Is the problem you are now having an issue with the lengths and area being returned do not seem to be the correct units? or are they correct units, but just seem to be off?

example: You request LinearUnit.Meters and it still returns Degrees? or You request LinearUnit.Meters and units are correct just the distances are off?

have you tried verifying your geometry against the rest service itself?
http://sampleserver3.arcgisonline.com/ArcGIS/rest/services/Geometry/GeometryServer/areasAndLengths

do the areas and lengths return the same values when you test against the REST service directly?

Re: Area And Perimeter

NathalieNeagle — Wed, 13 Oct 2010 23:18:23 GMT

Chris,

Thanks for the reply.

For testing sake, I started over straight from the SDK example.
http://help.arcgis.com/en/webapi/silverlight/samples/start.htm#AreasAndLengths

The only code I changed was:

I change the service to use ESRI DECIMAL DEGREEs

<esri:ArcGISTiledMapServiceLayer ID="StreetMapLayer"
          Url="http://services.arcgisonline.com/ArcGIS/rest/services/ESRI_Street_Map_2D/MapServer" />
         <esri:GraphicsLayer ID="MyGraphicsLayer" />

and I commented out the setting of static world mecator extent.

private static ESRI.ArcGIS.Client.Projection.WebMercator mercator =
            new ESRI.ArcGIS.Client.Projection.WebMercator();

and

ESRI.ArcGIS.Client.Geometry.Envelope initialExtent =
                    new ESRI.ArcGIS.Client.Geometry.Envelope(
                mercator.FromGeographic(
                    new ESRI.ArcGIS.Client.Geometry.MapPoint(-130, 20)) as MapPoint,
                mercator.FromGeographic(
                    new ESRI.ArcGIS.Client.Geometry.MapPoint(-65, 55)) as MapPoint);

            initialExtent.SpatialReference = new SpatialReference(102100);

            MyMap.Extent = initialExtent;

Then I changed the code that you told me to change to:

geometryService.AreasAndLengthsAsync(graphicList, LinearUnit.SurveyMile, LinearUnit.SurveyMile, null);

Basically I'm drawing a polygon around North America and its stating 0 sq miles and .003 polygon perimeter.

Nathalie

Re: Area And Perimeter

ChristineZeller — Thu, 14 Oct 2010 17:18:39 GMT

Chris,

I'm not sure how to verify the geometry against the rest service itself?
http://sampleserver3.arcgisonline.co...reasAndLengths
I'm not sure what to put in for polygon and length values.

My problem seems very similar to Nathalie's, I also just took the time to start from scratch but I'm trying to convert to meters and then do the calculation to miles.....unlike Nathalie just going straight to miles and commenting out the meters to miles math conversion. I'm getting very similar results as Nathalie stated no matter how big I make my polygon I get 0 sq miles and .00? perimeter.

I can also post my code but at this point like Nathalie I'm trying to work with the bare bones and just using the sdk example.

I'm commenting out the lines

private static ESRI.ArcGIS.Client.Projection.WebMercator mercator =
            new ESRI.ArcGIS.Client.Projection.WebMercator();

should I be declaring the 4326 projection

Also like Nathalie stated instead of using this service
Url="http://services.arcgisonline.com/ArcGIS/rest/services/World_Street_Map/MapServer"

I'm using

http://services.arcgisonline.com/ArcGIS/rest/services/ESRI_Imagery_World_2D/MapServer

I'm still doing

geometryService.AreasAndLengthsAsync(graphicList,LinearUnit.Meter, LinearUnit.Meter, null);




                   }

        private void GeometryService_AreasAndLengthsCompleted(object sender, AreasAndLengthsEventArgs args)

        {
            //TODO: Geometry service not returning correct values, area unit seems invalid, may need to use data in
            //planar coordinate space

               // convert results from meters into miles and sq meters into sq miles for our display
            double miles = args.Results.Lengths[0] * 0.0006213700922;
            double sqmi = Math.Abs(args.Results.Areas[0]) * 0.0000003861003;
            ResponseTextBlock.Text = String.Format("Polygon area: {0} sq. miles\nPolygon perimeter: {1} miles.", Math.Round(sqmi, 3), Math.Round(miles, 3));

        }

Not Sure what to do.

Thanks
Christine

Re: Area And Perimeter

ChristineZeller — Fri, 15 Oct 2010 16:48:57 GMT

Nathalie,

Have you made any progress?

Chris,

Do you have any other suggestions based on what Nathalie and I have posted. By the sounds of it seems like this should be working?

Christine

Re: Area And Perimeter

JenniferNery — Sun, 17 Oct 2010 00:28:51 GMT

You can test if you will get the same results if you made your request directly to the REST service as you would in your SL app, this way...

1. Download Fiddler from: http://www.fiddler2.com/fiddler2/version.asp, if you don't have it already.
2. Copy the query parameters from Fiddler's Inspectors WebForms section (as seen in the attached screenshot).
3. From your browser, go to: http://sampleserver3.arcgisonline.com/ArcGIS/rest/services/Geometry/GeometryServer/areasAndLengths and use the same parameters retrieved from step 2.

Re: Area And Perimeter

ChristineZeller — Mon, 18 Oct 2010 15:17:29 GMT

Jennifer,

Thanks for the reply. I walked through your example and I was able verify my geometry results against the rest service itself. I've attached the screen shot. I'm still getting very small numbers (Zero) or negitive numbers (when hitting the rest itself) and I'm selecting entire countries or even continents.

It seems like Nathalie and myself are doing the exact samething and getting the exact same results.

Here's my delima/question/request. We both started from sctrach and are using the SDK example with no other code. All we are doing are trying to use the ESRI StreetMap World 2D service (http://services.arcgisonline.com/ArcGIS/rest/services/ESRI_StreetMap_World_2D/MapServer), which uses 4326 instead of the World_Street_Map (http://services.arcgisonline.com/ArcGIS/rest/services/World_Street_Map/MapServer), which uses the 102100 spatial ref.

In the code behind we are both commenting out the following lines, which seems like it is just constraining the extent and setting the ref.....in our code our ref is defined by the one and only service add in our xaml (spatial 4326).

ESRI.ArcGIS.Client.Geometry.Envelope initialExtent =
                    new ESRI.ArcGIS.Client.Geometry.Envelope(
                mercator.FromGeographic(
                    new ESRI.ArcGIS.Client.Geometry.MapPoint(-130, 20)) as MapPoint,
                mercator.FromGeographic(
                    new ESRI.ArcGIS.Client.Geometry.MapPoint(-65, 55)) as MapPoint);

            initialExtent.SpatialReference = new SpatialReference(102100);

            MyMap.Extent = initialExtent;

Also like Chris suggest we are both changing the line of code:
GeometryService.AreaAndLengthsAsync(myGraphics), and Chris has verified that myself and Nathalie are both doing it correctly, each are different but both correct.

So it seems like something else is going on. Has someone else successfully changed the SDK example: http://help.arcgis.com/en/webapi/silverlight/samples/start.htm#AreasAndLengths to use the 4326 ref.

Re: Area And Perimeter

NathalieNeagle — Tue, 19 Oct 2010 17:30:09 GMT

Christine,
Your last description and explanation was exactly what I keep thinking. I have not made any progress. I�??m thinking we are missing some easy thing and sooner than later someone will direct us to the light.
Nathalie

Re: Area And Perimeter

JenniferNery — Wed, 20 Oct 2010 16:43:21 GMT

Try to draw your polygon in clockwise direction instead of counterclockwise or call simplify on the graphic (http://help.arcgis.com/en/webapi/silverlight/samples/start.htm#Simplify) before GeometryService.AreaAndLengthsAsync()

Re: Area And Perimeter

RyanDanford — Wed, 20 Oct 2010 20:16:47 GMT

Nathalie,

I encountered the same problem with a project and found that I could get accurate results by reprojecting the drawn graphic then measuring off the reprojection results. The approach is a bit slower, but you will get the results expected.

Re: Area And Perimeter

NathalieNeagle — Sun, 24 Oct 2010 02:03:23 GMT

Jennifer and Ryan Thanks for the replies!

Nathalie,

I encountered the same problem with a project and found that I could get accurate results by reprojecting the drawn graphic then measuring off the reprojection results. The approach is a bit slower, but you will get the results expected.

Ryan, would you mind sharing your code. I've had this problem for awhile now and I just can't seem to get it solved. My experience coding level is low so I'm not sure how to go about what you are suggesting.

Jennifer

It does not matter which way I draw the polygon (clockwise or counterclockwise) I took a look at the link you post and I really have no clue what to do with that can you point me in a more specific direction.

"Try to draw your polygon in clockwise direction instead of counterclockwise or call simplify on the graphic (http://help.arcgis.com/en/webapi/sil...t.htm#Simplify) before GeometryService.AreaAndLengthsAsync() "

Re: Area And Perimeter

JenniferNery — Sun, 24 Oct 2010 02:28:19 GMT

I ran Fiddler while running our SDK sample on Area and Perimeter and I was able to reproduce the negative Area by drawing the polygon in counter-clockwise direction. This is without any change to the code. When I drew the polygon in clockwise direction, the Area I get is correct.

The best way to avoid incorrect values for Area is to call SimplifyAsync() on the Geometry after draw is complete before calling AreaAndLengthAsync(). You can also try to draw in clockwise direction and you should see the difference in values.

This is the link to the Simply sample:
http://help.arcgis.com/en/webapi/silverlight/samples/start.htm#Simplify

Another option is to use the Editor's Add instead of the Draw object, this will ensure that the polygon is simplified before adding to your layer. Look at the Add Polygon button in this sample: http://help.arcgis.com/en/webapi/silverlight/samples/start.htm#EditToolsExplicitSave
If you will be using this approach on GraphicsLayer, the CommandParameter need to be set to the polygon symbol, the GraphicsLayer need to have its ID property set, the button's DataContext need to be set to an Editor with Map property bound to the map that contains this GraphicsLayer, and LayerIDs property set to the ID of the GraphicsLayer that will contain the polygon.