Assembling Cloud-Based Geographic Information Systems: A Pragmatic Approach Using Off-the-Shelf Components - Cloud Computing with e-Science Applications - page 152

Cloud Computing with E-science Applications
Same SRID with location inside region
Different SRID with location inside region
Same SRID with location outside region
FIGURE 7.5
Example of s selection of points in a polygon.
Integrated [code-based] Query) and sends it to the WCF-RIA service, which
then sends its equivalent SQL query to SQL Azure. The server then processes
the query and sends back results to the WCF-RIA services, which then send
enumerable entity objects to the client. Subsequently, Bing Maps object parser
converts WKT region data into maps objects to be displayed on the map.
Finally, the user selects the region and some accident search criteria to execute
a search; as a result, the same process is performed to display the accident loca-
tions as pushpins on the map. The overall interaction is presented in Figure 7.4.
Note that, in this particular application, finding an accident in a region
requires selection of points in a polygon. This is done using the STContains
geometry function of SQL Azure, which determines if a geometry object,
more specifically a spatial reference system identifier (SRID), is within
a region. This function returns 1 if an object s , represented by an SRID,
is inside a region and 0 otherwise, as shown in Figure 7.5. This functionality
is particularly suitable for the Cloud as it enables demanding processing to
be remotely commissioned.
7.4.1 Scaling and Fault Tolerance
Figure 7.6 represents a case in which three instances of our GIS applica-
tion are running in the public Azure cloud. The three web roles repre-
sent three separate web servers running three copies of GIS applications