Tag Archives: .NET

In this post, guest author Sam Berg of ESRI Boston explains how to link map tips to a GeoRSS feed using the Web ADF:

The ArcGIS Server 9.2 Web ADF provides a very useful capability in its support of web-tier graphics resources. Because the underlying map services in an application are not therefore required to draw all content, the web application instead can not only add dynamic data directly, but also more efficiently manage this custom content of the web map. The ArcGIS Server framework will take care of rendering all the data- we just need to customize the application to load into the web-tier graphics resources the content that our users will be interested in seeing.

When you combine adding data to your map at run time along with utilizing the out of the box MapTips web control, there is a real opportunity to build some easy-to-use web maps, complete with pop-up map tips for the added content.

Perhaps one of the most natural use cases for this kind of approach would be to plot GeoRSS feeds from a published resource on the web. GeoRSS feeds contain what you might expect: XML content encoded with associated geographic coordinates. There are a variety of sources for this content, and one great example is one from the USGS Earthquake Center that contains the location and magnitude information for worldwide earthquake activity over the past 24 hours (http://earthquake.usgs.gov/eqcenter/recenteqsww/catalogs/eqs1day-M2.5.xml).

There are some good GeoRSS feeds out there, but what about all the RSS news feeds that you are currently viewing with your favorite online RSS aggregator? Actually, there are a few web services out there that will read a designated RSS feed and return for you a GeoRSS version with <geo:lat> and <geo:lon> tags. Nice!

The web service I use in this example is from GeoNames.org. Their web service, described here, simply takes a “feedURL” parameter and returns for you a version of the XML with coordinates for the matches it finds.

For example, sending the BBC News World Edition Front Page feed which includes an item about heavy rains in Australia:

<item>

<title>Heavy rains hit parched Australia</title>

<link>http://news.bbc.co.uk/go/rss/-/2/hi/asia-pacific/6670333.stm</link>

<description>Farmers get welcome relief from a six-year drought, as the heaviest rain for years soaks south-eastern Australia.</description>

</item>

…to the GeoNames.org web services by using this format:

http://ws.geonames.org/rssToGeoRSS?feedUrl=http://news.bbc.co.uk/rss/newsonline_world_edition/front_page/rss.xml

…will result in a feed being returned which includes the updated item with GeoRSS point tags added:

<item>

<title>Heavy rains hit parched Australia</title>

<link>http://news.bbc.co.uk/go/rss/-/2/hi/asia-pacific/6670333.stm</link>

<description>Farmers get welcome relief from a six-year drought, as the heaviest rain for years soaks south-eastern Australia.</description>

<geo:lat xmlns:geo=”http://www.w3.org/2003/01/geo/wgs84_pos#”>-25.0</geo:lat>

<geo:long xmlns:geo=”http://www.w3.org/2003/01/geo/wgs84_pos#”>135.0</geo:long>

</item>

So I have now in this feed spatially referenced items, along with <TITLE>, <LINK>, and <DESCRIPTION> tags from which to generate map tips. Starting with a simple web map page, what I’ll do next is write some code to dynamically populate a graphics resource with “graphic feature elements” derived from the designated GeoRSS feed, and configure the map to generate map tips for the new data. Along the way I’ll also wire up a few AJAX callbacks to support the application communication.

First, I’ll set up a simple web map with a dropdown for a few GeoRSS feeds, a MapResourceManager configured with a basemap resource and a graphics resource, a Toolbar, and a MapTips control. Finally, I have also added a “BuddiedCallbackButton”. This control is based on Ryan Olson’s excellent CallbackButton post, and I added to the code to be able to pass a collection of values to the callback handler from associated buddy controls, allowing in this case the URL of the selected GeoRSS feed in the dropdown to be used.

When the “Add” command is clicked, I’ll set up a graphics layer in the “GeoRSSFeed” graphics resource. As described in the online EDN documentation, there are two graphics layer types, ElementGraphicsLayers, and FeatureGraphicsLayers. I’ll choose to generate a FeatureGraphicsLayer since these are best suited for storing attributes with the elements, which I’ll need to configure the map tips with. Since I know the GeoRSS feeds in this example all contain <TITLE>, <LINK>, and <DESCRIPTION> tags, I’ll set up the graphics layer to also maintain these attributes.

Next, I’ll use the .NET System.XML assembly to read and parse the selected GeoRSS feed. For each item in the feed, I’ll try to find the <geo:lat> and <geo:lon> tags, as well as the <TITLE>, <LINK>, and <DESCRIPTION> tags and store these in a StringDictionary.

As long as a coordinate was found for the item, I’ll add a new graphic element to the graphics layer and populate its attributes from the StringDictionary that was populated from the feed items.

Here’s the main code block to read the GeoRSS feed, parse for coordinates and attributes, and populate a graphics layer from the results:

    //note that the application could expose different values for the URL and maptips format tag:

    string sURL = “http://earthquake.usgs.gov/eqcenter/recenteqsww/catalogs/eqs1day-M2.5.xml”;

    string sBodyFormat = “Earthquake:<BR>{DESCRIPTION}<BR> <a target=_new href= {LINK} > {LINK} </A> <BR> <img src=’http://earthquake.usgs.gov/te
mplate/images/header_graphic_usgsIdentifier_white.jpg’>”;

    #region load RSS feed

    XmlDocument _doc = new XmlDocument();

    String UrlString;

    //Build RSS Request String

    UrlString = sURL;

    //Load RSS document

    _doc.Load(UrlString);

    //Navigator and Iterator used to parse RSS

    System.Xml.XPath.XPathNavigator nav = _doc.CreateNavigator();

    System.Xml.XPath.XPathNodeIterator nodeItrItems = nav.Select(“//item”);

    int iCount = 0;

    //Loop through each item witin RSS

    while (nodeItrItems.MoveNext())

    {

      StringDictionary pValues = new StringDictionary();

      System.Xml.XPath.XPathNodeIterator nodeItrChildren = nodeItrItems.Current.SelectChildren(System.Xml.XPath.XPathNodeType.Element);

      ESRI.ArcGIS.ADF.Web.Geometry.Point pIncident = new ESRI.ArcGIS.ADF.Web.Geometry.Point();

      pIncident.Z = 100;

      ESRI.ArcGIS.ADF.Web.Display.Symbol.SimpleMarkerSymbol pSymbol = new ESRI.ArcGIS.ADF.Web.Display.Symbol.SimpleMarkerSymbol();

      ESRI.ArcGIS.ADF.Web.Display.Symbol.TextMarkerSymbol pText = new ESRI.ArcGIS.ADF.Web.Display.Symbol.TextMarkerSymbol();

      System.Drawing.Color pColor = new System.Drawing.Color();

      pColor = System.Drawing.Color.Red;

      pSymbol.Type = ESRI.ArcGIS.ADF.Web.Display.Symbol.MarkerSymbolType.Star;

      pSymbol.Width = 20;

      pSymbol.Color = pColor;

      //Loop through each child node and extract information

      while (nodeItrChildren.MoveNext())

      {

        string str = nodeItrChildren.Current.Name;

       
if (str == “geo:lat” || str == “LATITUDE”)

        {

          pIncident.Y = Convert.ToDouble(nodeItrChildren.Current.InnerXml);

          pIncident.Z = 0;

        }

        else if (str == “geo:long” || str == “LONGITUDE”)

        {

          pIncident.X = Convert.ToDouble(nodeItrChildren.Current.InnerXml);

          pIncident.Z = 0;

        }

        else if (pFields.Contains(str.ToUpper()))

        {

          string s = nodeItrChildren.Current.InnerXml;

          s = HttpUtility.HtmlDecode(s);

          pValues.Add(str.ToUpper(), s);

        }

      }

      if ((pIncident.Z != 100))//just using Z = 100 as code for unlocated

      {

        DataRow row = glayer.Add(pIncident);

        for (int ii = 0; ii < pFields.Count; ii++)

        {

          row[pFields[ii].ToString()] = pValues[pFields[ii].ToString()].ToString();

        }

        iCount++;

      }

      if (iCount >= 100)//stop after loading 100 feed items

      {

        break;

      }

    }

    #endregion

At this point, I have a graphics layer populated with point elements derived from the specified GeoRSS feed. I need to now configure the MapTips control to use this layer:

 

 #region update MapTips

    MapTips1.Features = null;

    MapTips1.Layer = “MapResourceManager1::GeoRSSFeed::GeoRSS Results”;

    MapTips1.Map = this.Map1.ID;

    MapTips1.FeatureLimit = 100;

    MapTips1.HeaderFormatString = “{TITLE}”;

    MapTips1.BodyFormatString = sBodyFormat;

    MapTips1.Refresh();

    #endregion

A very useful property of the graphics layer is that we can ask it for its geographic bounding box. Since I want to automatically zoom the map to this extent, I can use this property instead of having to write code to loop through all the coordinates of the feed items which were added.

Finally, I’ll add the MapTips and Map controls’ CallbackResults collections to the CallbackButton. In these callback results collections will be a lot of instructions to the processCallbackResult ESRI javascript handler on how to generate MapTips for the graphics layer and what in the map needs updating.

Since the MapTips’ BodyFormat property will honor both fields from the associated layer, as well as standard HTML formatting tags, we can mix and match these to come up with some nicely formatted MapTip pop-up windows when a feed point is clicked.

switch (sURL)

    {

      //USGS Recent Earthquakes:

      case “http://earthquake.usgs.gov/eqcenter/recenteqsww/catalogs/eqs1day-M2.5.xml”:

        sBodyFormat = “Earthquake:<BR>{DESCRIPTION}<BR> <a target=_new href= {LINK} > {LINK} </A> <BR> <img src=’http://earthquake.usgs.gov/template/images/header_graphic_usgsIdentifier_white.jpg’>”;

        break;

      //Google News Headlines:

      case “http://ws.geonames.org/rssToGeoRSS?feedUrl=http://news.google.com/nwshp?output=rss”:

        sBodyFormat = “{DESCRIPTION}”;

        break;

      //BBC World News:

      case “http://ws.geonames.org/rssToGeoRSS?feedUrl=http://news.bbc.co.uk/rss/newsonline_world_edition/front_page/rss.xml”:

        sBodyFormat = “{TITLE}:<BR><a target=_new href= {LINK} > {LINK} </A> <BR>”;

        break;

    }

 

So that’s about it. Using web-tier graphics layers in the ArcGIS Server ADF can be a great way of adding dynamic data to your web map application, whether it be from existing XML-based internet feeds, or your own custom data generated by your application.

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