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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B-YF. Istanbul 2004
2.3 Application Development
In this study a GIS application was developed and a web site
was configured to serve the earthquake information on the
Internet. MapObjects activex component was added to a form in
Visual Basic project file and used to develop the application
(Figure 5). WebLink.ocx is also an activex control. This
control is installed automatically with MOIMS. Its role is to
listen on an assigned port for requests from a client and
communicate with the esrimap.dll. Esrimap.dll is a dynamic
link library component that extends web server software. It can
manage requests and responses from map server and administer
map services (ESRI, 1998). Following functions can be
implemented in programs built with Map Objects control:
e Display a map with multiple map layers, such as
roads, streams and boundaries.
e Pan and zoom throughout a map.
e Draw graphic features such as points, lines, ellipses,
rectangles and polygons.
e. Draw descriptive text.
e Identify features on a map by pointing at them.
e Select features along lines and inside boxes, areas,
polygons, and circles.
e Select features within a specified distance of other
features and more...(ESRI, 1999).
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Figure 5: Visual Basic project with components
The map control is the main object of the MapObjects. The map
control is a container for the maps. Maps are displayed on this
container. MapObjects ActiveX control has lots of properties,
events and controls. Main properties are CoordinateSystem,
Extent, FullExtent, MousePointer and Visible. Main methods
are DrawShape, ExportMap, Pan, Refresh and TrackRectangle.
Main events are AfterLayerDraw, | BeforeLayerDraw,
MouseDown and MouseMove. Before adding any vector layer
a data connection must be established. A data connection
represents a connection to a source of geographic data. In this
study a folder containing shapefiles is the data source. A
connection can return a GeoDataSets collection. Each member
of the collection, referred to as GeoDataset, represents a
discrete set of geographic data that can be retrieved from the
data source. Geographic data in a GeoDataset is used by
assigning it to the GeoDataset property of a new | MapLayer
object. The Connect method of the DataConnection object will
attempt to connect to the data source specified in the Database
property. Following is the codes for adding layers to the
application:
147
add shapefiles
Dim dc As New DataConnection
Dim Lyr As MapObjects2. MapLayer
dc.Database — ImsDataPath
If Not dc.Connect Then
MsgBox "ims data set not found"
End
End If
Set Lyr = New MapLayer
Set Lyr.GeoDataset = de. FindGeoDataset("Seismic")
Lyr.Symbol.SymbolType = moPointSymbol
Lyr.Symbol.Style = moSquare Marker
Lyr.SymbolColor = moRed
Lyr.Symbol.Size = 9
Lyr. Visible = False
Map. Layers. Add Lyr
2.4 Serving on the Internet
GIS application runs together with MapObjects Internet Map
Server components. MapObjects Internet Map Server acts as a
gateway between Web Server and the mapping application. The
request made by the client is passed to the web server first. The
server recognizes that this request is about creating a map, so it
directs it to the map server. The map server executes the
application according to the type of mapping demand (this
demand can be a display operation like a zoom-in function or a
query about a feature) and sends the result (a picture of the map
in JPEG format) to the web server. The web server brings the
HTML page created to the client. MapObjects IMS has three
different components that runs one after the other. IMS Catalog,
IMS Launch, and IMS Admin are connected to each other. IMS
Admin communicates with IMS Catalog to manage the state,
running or not, of a map service. IMS Catalog communicates
with IMS Launch. When starting a map service, IMS Catalog
sends the path and file name of the map service to be started
and the number of instances to start. IMS Launch responds by
starting the map service.
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Figure 6: Server side of the application
When a client sends a URL request to the server that hosts
esrimap.dll, it determines which map service to communicate to
respond the request. The URL address : http://ServerName/
scripts/esrimap.dll?Name-MapServiceName&Cmd-Map. Each
argument and value pair is referred to a query parameter. The
