Wednesday, April 25, 2012

ARCGIS JavaScript API – USING BASIC GIS TOOLS AND COMMANDS – PART IV


1.     Introduction

 In previous articles I showed you how we can setup a map  infrastructure for consuming different dynamic layers and feature layers. I showed you how we can build  different tables with information coming from these layers. In this article I will introduce you in the creation of some basic command and tools that will interfere with the layers in the map. In the implementation of these actions I will use more actively the ViewModel  pattern found in the knockoutJS  javascript  library.

2.     Toolbar

The toolbar that will be discussed in this article consist of the following toolbar items :

·         Zoom In tool
·         Zoom out tool
·         Pan command
·         Inspect tool
·         Measure tools






All these tools and commands have their main implementation in the common ViewModel but have a more detailed implementation in a ‘common toolbar’ ViewModel. Doing so, the main ViewModel is a light weight class with little or no logic behind, and it sole purpose is to interact  with the view (the html page). New here is also the use of templates from the knockoutJS  javascript  library.
3.     Logging

To make debugging easier, I introduced a logging component. The logging happens through a rest service and is stored in a log file at the server. This approach can be useful to  trace all errors that occurs in the application. However for debugging purpose this can also be very useful. Because a lot of methods works asynchronous, having an extended log file can help you debug errors due to inconsistent sequence of operations. Below you can see an example of a log file. I use a debug variable to enable or disable extended logging. Important is adding logging when asynchronous actions occurs. As you can see in de log file example, initialization does not always happens in the sequence of the call to the rest services.

24/04/2012 - 18:05:30 - I - startup - getconfiguration start
24/04/2012 - 18:05:30 - I - startup - getconfiguration finished
24/04/2012 - 18:05:30 - I - eventAggregator-subscribe - mapLoaded
24/04/2012 - 18:05:30 - I - eventAggregator-subscribe - legendBuild
24/04/2012 - 18:05:30 - I - addNewDynamicLayer - http://services.arcgisonline.com/ArcGIS/rest/services/World_Topo_Map/MapServer
24/04/2012 - 18:05:30 - I - addNewDynamicLayer - http://services.arcgisonline.com/ArcGIS/rest/services/World_Street_Map/MapServer
24/04/2012 - 18:05:30 - I - mapModule - init finished
24/04/2012 - 18:05:30 - I - startup - startup finished
24/04/2012 - 18:05:30 - I - layer_Initialized - http://services.arcgisonline.com/ArcGIS/rest/services/World_Topo_Map/MapServer
24/04/2012 - 18:05:30 - I - addNewFeatureLayer - http://sampleserver3.arcgisonline.com/ArcGIS/rest/services/Fire/Sheep/FeatureServer/0
24/04/2012 - 18:05:30 - I - addNewFeatureLayer - http://sampleserver3.arcgisonline.com/ArcGIS/rest/services/Fire/Sheep/FeatureServer/1
24/04/2012 - 18:05:30 - I - layer_Initialized - http://services.arcgisonline.com/ArcGIS/rest/services/World_Street_Map/MapServer
24/04/2012 - 18:05:31 - I - featureLayer_Initialized - http://sampleserver3.arcgisonline.com/ArcGIS/rest/services/Fire/Sheep/FeatureServer/1
24/04/2012 - 18:05:31 - I - featureLayer_Initialized - http://sampleserver3.arcgisonline.com/ArcGIS/rest/services/Fire/Sheep/FeatureServer/0
24/04/2012 - 18:05:31 - I - eventAggregator-publish - mapLoaded - initializeVM
24/04/2012 - 18:05:31 - I - eventAggregator-publish - mapLoaded - legendBuild
24/04/2012 - 18:05:31 - I - legendModule - start legend build
24/04/2012 - 18:05:33 - I - legendModule - build legend done
24/04/2012 - 18:05:33 - I - eventAggregator-publish - legendBuild - selectBuild


4.     Navigation tools

The migration of the Silverlight C# implementation of Zoom in and Zoom out is very easy. As you can see by comparing the two implementations, a lot of coding is similar between C# and JavaScript.

Button commands

JavaScript Code
/// <summary>
/// Zoom In task
/// </summary>
   zoomInTask: function () {
      currentCommand = "ZoomIn";
      iGisOperation.setCompleteDrawEvent(drawComplete);
      iGisOperation.setDrawMode(esri.toolbars.Draw.EXTENT); // Start draw tool with a rectangle
   },
/// <summary>
/// Zoom Out task
/// </summary>
   zoomOutTask: function () {
      currentCommand = "ZoomOut";
      iGisOperation.setCompleteDrawEvent(drawComplete);
      iGisOperation.setDrawMode(esri.toolbars.Draw.EXTENT); // Start draw tool with a rectangle
   }

C# Code

/// <summary>
/// Zoom In task
/// </summary>
  public void ZoomInTask()
  {
       currentCommand = "ZoomIn";
       gisOperations.SetCompleteDrawEvent(DrawComplete);
       gisOperations.SetDrawMode(DrawMode.Rectangle); // Start draw tool with a rectangle
  }
/// <summary>
/// Zoom out task
/// </summary>
  public void ZoomOutTask()
  {
       currentCommand = "ZoomOut";
       gisOperations.SetCompleteDrawEvent(DrawComplete);
       gisOperations.SetDrawMode(DrawMode.Rectangle); // Start draw tool with a rectangle
  }

Activation of the zoom action

JavaScript code
iGisOperation.mapZoom(currentCommand, args.getExtent());
iGisOperations.setDrawMode(esri.toolbars.Draw.EXTENT);


C# code

gisOperations.MapZoom(currentCommand, args.Geometry);
gisOperations.SetDrawMode(DrawMode.Rectangle);

Next I use the zoom in the map method, this is the  main method used for  the zoom in and  the zoom out actions. Below is the comparison between the JavaScript and C# code.

Zoom action

JavaScript Code
mapZoom: function (action, geometry) {
  try {
        var multiplier;
        if (action == "ZoomIn") {
            map.setExtent(geometry.getExtent());
        }
        Else if (action == "ZoomOut") {
            var currentExtent = map.extent;
            var zoomBoxExtent = geometry.getExtent();
            var zoomBoxCenter = zoomBoxExtent.getCenter();
            var whRatioCurrent = currentExtent.getWidth() / currentExtent.getHeight();
            var whRatioZoomBox = zoomBoxExtent.getWidth() / zoomBoxExtent.getHeight();
            var newEnv = null;
            if (whRatioZoomBox > whRatioCurrent) {
            // use width
                multiplier = currentExtent.getWidth() / zoomBoxExtent.getWidth();
               var newWidthMapUnits = currentExtent.getWidth() * multiplier;
               newEnv = new esri.geometry.Extent(zoomBoxCenter.x - (newWidthMapUnits / 2), zoomBoxCenter.y,
                zoomBoxCenter.x + (newWidthMapUnits / 2), zoomBoxCenter.y, map.spatialReference);
            }
            else {
            // use height
                multiplier = currentExtent.getHeight() / zoomBoxExtent.getHeight();
                var newHeightMapUnits = currentExtent.getHeight() * multiplier;
                newEnv = new esri.geometry.Extent(zoomBoxCenter.x, zoomBoxCenter.y - (newHeightMapUnits / 2),
               zoomBoxCenter.x, zoomBoxCenter.y + (newHeightMapUnits / 2), map.spatialReference);
            }
            if (newEnv != null)
                            map.setExtent(newEnv.getExtent());
                    }
     } catch (e) {
           throw new Error("zoom action failed. " + e.name + "\n" + e.message);
     }
}

C# code

/// <summary>
/// Zoom in and out task
/// </summary>
/// <param name="action">ZoomIn or ZoomOut</param>
/// <param name="geometry">Rectangle to be zoomed</param>
public void MapZoom(string action, ESRI.ArcGIS.Client.Geometry.Geometry geometry)
{
  try
    {
       if (action.Equals("ZoomIn"))
       {
         mapControl.ZoomTo(geometry as Envelope);
       }
       Else if (action.Equals("ZoomOut"))
       {
         Envelope currentExtent = mapControl.Extent;
         Envelope zoomBoxExtent = geometry as Envelope;
         MapPoint zoomBoxCenter = zoomBoxExtent.GetCenter();
         double whRatioCurrent = currentExtent.Width / currentExtent.Height;
         double whRatioZoomBox = zoomBoxExtent.Width / zoomBoxExtent.Height;
         Envelope newEnv = null;
         if (whRatioZoomBox > whRatioCurrent)
         // use width
         {
           double multiplier = currentExtent.Width / zoomBoxExtent.Width;
           double newWidthMapUnits = currentExtent.Width * multiplier;
           newEnv = new Envelope(new MapPoint(zoomBoxCenter.X - (newWidthMapUnits / 2), zoomBoxCenter.Y),
          new MapPoint(zoomBoxCenter.X + (newWidthMapUnits / 2), zoomBoxCenter.Y));
         }
         else
         // use height
         {
           double multiplier = currentExtent.Height / zoomBoxExtent.Height;
           double newHeightMapUnits = currentExtent.Height * multiplier;
           newEnv = new Envelope(new MapPoint(zoomBoxCenter.X, zoomBoxCenter.Y - (newHeightMapUnits / 2)),
           new MapPoint(zoomBoxCenter.X, zoomBoxCenter.Y + (newHeightMapUnits / 2)));
         }
         if (newEnv != null)
           mapControl.ZoomTo(newEnv);
     }
  }
  catch (Exception ex)
  {
       messageBoxCustom.Show(String.Format("MapZoom-{0}", ex.Message),
       GisTexts.SevereError,MessageBoxCustomEnum.MessageBoxButtonCustom.Ok);
  }
}

As you can see for the two different language environment,  the same logic can be used for the two  projects.  The fact that the same code can be used is mainly due that both environments are based on the ArcGis Api’s that on its turn is based on the rest services from the ArcGis server. 

5.     Inspect tool

With the inspect tool we come to a more sophisticated tool. The inspect tool will retrieve all features that intersects with the point  indicated on the map using a predefined buffer.  The layers used on the map for the query must be checked on the selection tab of the tab control.  The results containing the attributes will be displayed on the query tab. To simplify the display, I used a html embedded template of knockoutJS that make use of dependency properties of the ViewModel easy to show.

Step 1 : Start a draw action of a point selection.

infoCommand: function () {
  try {
    iGisOperation.getMeasurement().clearResult();
    iGisCommonTasks.setFinishedInfoEvent(handleInfoResults);
    iGisCommonTasks.infoQuery(true);
  } catch (e) {
    logMessage("E", "IQ-01", e.Message);
  }
 }

Step 2: Start the draw action in the infoQuery method. When the tool is finished, the result will be returned in the callback function  ‘handleInfoResults’

        infoQuery: function (isSpatialQuery) {
            // Info implementation , using ESRI API
            iGisOperation.resetCompleteDrawEvent(drawComplete);
            if (isSpatialQuery)
                currentCommand = "Info";
            else
                currentCommand = "AddressInfo";
            iGisOperation.setCompleteDrawEvent(drawComplete);
            iGisOperation.setDrawMode(esri.toolbars.Draw.POINT);
        }
Step 3: Start the spatial query for all the selected layers.

if (currentCommand == "Info" || currentCommand == "AddressInfo") {
  // Use ESRI API for Info
  var layer = null;
  var i;
  var query, queryTask;
  iGisOperation.setDrawMode(null);
  iGisOperation.resetCompleteDrawEvent();
  result = new Array();
  errorCount = 0;
  errorMessages = '';
  totalCountLayers = 0;
  currentCountLayers = 0;
  if (currentCommand == "Info") {
    totalCountLayers = iGisOperation.getLayersSelectionInfos().length;
    for (i = 0; i < iGisOperation.getLayersSelectionInfos().length; i++) {
      if (iGisOperation.getLayersSelectionInfos()[i].selected && iGisOperation.getLayersSelectionInfos()[i].layer.type == 'Feature Layer') {
        queryTask = new esri.tasks.QueryTask(iGisOperation.getLayersSelectionInfos()[i].url);
        query = new esri.tasks.Query();
        query.geometry = args;
        query.outFields = ["*"];
        query.spatialRelationship = esri.tasks.SPATIAL_REL_INTERSECTS;
        queryTask.execute(query, function (features) {
           currentCountLayers += 1;
           if (!features.name) {
              if (features.features.length > 0)
                 result.push(features);
           }
           queryInfosComplete();
        }, function (e) {
           currentCountLayers += 1;
           errorCount += 1;
           errorMessages += ">";
           errorMessages += e.message;
           errorMessages += "\n";
           queryInfosComplete();
         });
       }
       else
         currentCountLayers += 1;
    }
  }

The function ‘queryInfosComplete’ is used to verify if all layers has been handled, if this is the case, the callback function is called to handle over the results to the view model.
    function queryInfosComplete() {
        if (currentCountLayers >= totalCountLayers) {
            if (finishedInfoOperation != null)
                finishedInfoOperation(result);
        }
    }

Step 4: Handle the results to the calling view model. We build here a list of all attributes found and that is used to scroll through.

    var attributesResults;
    var currentItem;
    function handleInfoResults(results) {
        try {
            iGisCommonTasks.setFinishedInfoEvent(null);
            attributesResults = new Array();
            var attributeItem;
            for (var i = 0; i < results.length; i++) {
                var resultFeatures = results[i].features;
                for (var j = 0; j < resultFeatures.length; j++) {
                    var attributes = new Array();
                    for (var item in resultFeatures[j].attributes) {
                        attributeItem =
                            new attribute(ko.observable(item), ko.observable(resultFeatures[j].attributes[item]));
                        attributes.push(attributeItem);
                    }
                    attributesResults.push(attributes);
                }
            }
            if (attributesResults.length > 0) {
                viewModel.resultAttributes(attributesResults[0]);
                viewModel.resultCount((attributesResults.length));
                currentItem = 1;
                viewModel.resultIndex(currentItem);
                viewModel.resultVisible(true);
            }
            else {
                alert("No results found");
            }
        } catch (e) {
            logMessage("E", "error in handleInfoResults->" + e.name + "\n" + e.message, "commonToolbarVM");
        }
    }
An array of attributes is extracted from the results is used to display attributes of one feature at a time.
Two buttons are used  to scroll through the results. The query tab looks like the example below.





The html code that is used for displaying the result above with the knockoutJS data binding is :
<div id="queryResults" data-bind="visible: resultVisible">
   <table class="tableResult">
       <thead ><span data-bind="text: resultHeader" style="font-size:medium"/>
            <th scope="col">Field</th>
            <th scope="col">Value</th>
       </thead>
       <tbody data-bind="foreach: resultAttributes">
            <tr>
                <td data-bind="text: field">
                </td>
                <td data-bind="text: value">
                </td>
            </tr>   
        </tbody>
   </table>
   <input id="nextResult" type="button" value="Next"  data-bind="click: nextResultExecute, enable: nextResultCanExecute" />
   <input id="prevResult" type="button" value="Previous" data-bind="click: prevResultExecute, enable: prevResultCanExecute" />
   <input id="closeResult" type="button" value="Close" data-bind="click: closeResultExecute, enable: closeResultCanExecute"  />
</div>

6.     Measure tools

In the Silverlight ArcGis API, this is a simple tool that can be implemented without writing custom code. The implementation happens through the interaction library from blend.
In JavaScript the job is much harder if you don’t want to use the ESRI widget and create your own button implementation. Creation of a custom measurement consist of the following steps:
·         Add the measurement widget to the html page during the onload event of the map.
·         Activate the measure tools through button commands.
·         In the callback method the geometry drawn is returned.
·         Call the geometry service for calculating area and length of the drawn geometry.
·         Return the values to the ViewModel for displaying .

Step : Add measurement widget in the init method of the map module

            dojo.connect(mapControl, 'onLoad', function (map) {
                //resize the map when the browser resizes
                dojo.connect(dijit.byId('map'), 'resize', map, map.resize);
                initToolbar(map);
            });
Step: Activate the measure tool in the widget.

measureCommand: function (tool) {
   iGisOperation.getMeasurement().clearResult();
   iGisOperation.getMeasurement().setTool(tool, true);
   dojo.connect(iGisOperation.getMeasurement(), "onMeasureEnd", function
      (activeTool, geometry) {
      this.setTool(activeTool, false);
      // calcuate the area or length of the geometry 
      if (activeTool == "area") {
        iGisGeoProcessing.calculateAreaLength(geometry, function
          calcResults(areaPolygon, lenPolygon) {
          if (areaPolygon != null)
           viewModel.message1("Area is " + areaPolygon.toFixed(0) + " m2 and the length is " + lenPolygon.toFixed(0) + " m");
          else
            viewModel.message1("Error occured during the calculation, see log file");
         });
       }
       else if (activeTool == "distance") {
         iGisGeoProcessing.calculateLength(geometry, function calcResults(lenPolyline) {
           if (lenPolyline != null)
             viewModel.message1("Length is " + lenPolyline.toFixed(0) + " m");
           else
             viewModel.message1("Error occured during the calculation, see log file");
          });
        }
      });
 }

Step  Calculate the area or length.

Two methods are added to the geo processing class to calculate the area and / or length of geometries. Later I will add more methods to this class for supporting the feature editing to
calculateAreaLength: function (geometry, callBack) {
   var areasAndLengthParams = new esri.tasks.AreasAndLengthsParameters();
   areasAndLengthParams.lengthUnit = esri.tasks.GeometryService.UNIT_METER;
   areasAndLengthParams.areaUnit = esri.tasks.GeometryService.UNIT_METERS;
   iGisOperation.getGeometryService().simplify([geometry],
      function (simplifiedGeometries) {
         areasAndLengthParams.polygons = simplifiedGeometries;
         iGisOperation.getGeometryService().areasAndLengths(areasAndLengthParams,
            function outputAreaAndLength(result) {
               var areaPolygon = result.areas[0];
               callBack(result.areas[0], result.lengths[0]);
            }, function errorAreaLength(err) {
            logMessage("E", "calculate area failed -->" + err.message, "commonToolbarVM");
                 callBack(null,null);
         });
   });
}

7.     Conclusion

By implementing these tools we already touched a lot of geometry processing. In the case of the inspect tool, I discover one important difference when executing spatial queries. In the Silverlight API you can add a tag to the query, so when the results are returned from the query, the tag can be used to identify the result set.  In the JavaScript API, no tag can be added to the query. The result of this is that I could not identify the origin (layer) from the features. I will later see if there is a way to work around this lack of information in the JavaScript API.

The use of geometry services will play an important role when we start to do feature editing. In the next document I will introduce some basic editing functionality.

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