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Design and Architecture V 1.5 |
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Client Side Since GeoSurf is interface-driven, it makes narrative sense to discuss the client components first. The client-side of GeoSurf consists of a Java applet developed by CAST. Included in this applet are commercial third party Java classes used to provide certain elements of the graphical user interface. The applet uses each of the several servlets, to be discussed later, as necessary to interface with the Oracle database. The applet is Swing-based and thus requires the Java 1.3 plug-in from Sun. Each of the four major graphical user interface components will be presented as they appear on the screen and their internal functionality will be discussed. Data Lister
Figure 3. An illustration of the DataLister and its subcomponents. The Datalister is primarily a container class to hold the LayerListerClient2 and the MetadataClient. It has buttons which activate the metadata filter, the geographic filter, and the data downloader. LayerListerClient2 The LayerListerClient2 provides a visual display of the list of layers available for downloading. The LayerListerClient2 provides a list of layers titles filtered by metadata and geographic filters. The LayerListerClient2 catches events from the MetadataFilter and the Geographic filter containing the filter information. Each time the LayerListerClient2 catches an event it forwards the information to the LayerListerServlet, which returns a list of layers, filtered by the information provided. The new list is displayed as well as the filter information that was used to create the list. When a user clicks on a layer title the LayerListerClient2 throws an event with the layer name to the MetadataClient. MetadataClient The MetadataClient displays layer metadata information. The MetadataClient catches events containing the layer name from the LayerListerClient2. Then it sends that information to the MetadataServlet. The servlet returns the full layer metadata to the MetadataClient. The metadata client displays the information from the metadata servlet in two forms. The short form contains the most useful information about the layer including its title, the publication date, its abstract, and its purpose. The long form contains a complete record of FGDC compliant metadata. MetadataFilter
Figure 4. This figure shows Metadata Filter tool. The MetadataFilter is accessed by clicking on the Metadata Filter button of the DataLister and is used to specify metadata filtering criteria. Once
the user has specified the metadata criteria, a click on the Apply button
throws an event back to the DataLister, prompting it to update the list
of layers it presents. Geographic Filter a)
c)
Figure 5. This figure shows each of the tabbed-panels available in the GeographicFilter: a) the Point Location panel; b) the Bounding Box panel; and c) the Existing Polygon panel. For the Point Location and Bounding Box panels, a visual map interface is available (d) to help the user in selecting the area of interest. The GeographicFilter is accessed by clicking on the Geographic Filter button of the DataLister and is used to specify the geographic area of interest. The user can specify this area of interest in three ways: 1) (Figure 5a) by specifying a point location and border around it; 2) (Figure 5b) by specifying a bounding box; 3) (Figure 5c) by selecting a preexisting polygon. Options 1 and 2 can also be specified using a visual map display (Figure 5d). In specifying a point location, the user can enter coordinates in UTM or Lat/Lon or he can enter a street address. MapInfo's MapMarkerJ product is used for geocoding street addresses. MapMarkerJ consists of a servlet and a set of Java classes that are imported by the GeoSurf applet. In specifying a bounding box, the user enters the coordinates of two opposing corners in Lat/Lon. A visual map-based selection mode is available for each of these methods. This functionality uses MapInfo's MapXtremeJava product. MapXtremeJava consists of a servlet and a set of Java classes that are imported by the GeoSurf applet. These classes provide the visual map display and some basic map manipulation tools. Custom map tools were developed by CAST to provide the point location and bounding box functionality. The options presented in the Existing Polygon panel are derived from a specialized metadata table in the GeoStor database. The components of the Existing Polygon panel contact a servlet, the PolyPanelServlet, which bundles up the available polygon data and streams it back as a serialized object. The Existing Polygon panel then parses this object into the various selection boxes presented to the user. Once
the user has specified the geographic area of interest, a click on the
Apply button throws an event back to the DataLister, prompting it to update
the list of layers it presents. Download Wizard a)
c)
Figure
6. This figure shows the various panels of the DownloadWizard: a) the
Add-Remove panel, in which the user selects the layers to be downloaded;
b) the General Parameters panel, in which the user selects the projection;
c) the Vector Parameters panel (only presented if vector layers are to
be downloaded), in which the user specifies parameters relevant to vector
downloads; and d) the Email panel, in which the user enters his email
address for notification when his layers are ready. The DownloadWizard is accessed by clicking on the Download button of the DataLister and is used to select layers for download and specify their projection and data format. Download parameters are collected and sent to the DownloadServlet. When server side processing completes, the user is sent an email containing a URL from which he can download the finished product in the form of a zip file. This zip file contains the file or files representing the data layer in the format specified by the user. In addition, an html file is included containing metadata for the data layer. For vector data layers, the prj (projection) and csf (coordinate system file) files appropriate to the specified projection are included as well. These files are used by a variety of GIS software packages for reading and storing the projection of the data layer. Introduction | Client Side | Server Side |
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GeoStor
Design and Operational Considerations By Center
for Advanced Spatial Technologies
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d) 