GeognoSIS.NET and Web Services FAQ's
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This
document contains the answers to frequently asked questions (FAQ)
about GeognoSIS.NET and Web Services.
Questions in this FAQ:
- How do I check the number of processors
on my server?
- What is the difference between
the ASC and GeognoSIS.NET?
- What are Web Mapping Servers (WMS)
and Web Feature Servers (WFS) and how can I use them?
- What options do I have when developing
web sites?
- How can I use GeognoSIS.NET through
a firewall?
- How can I convert an ASC
application to run on GeognoSIS.NET?
1)
Question: How do I check the number of processors on my server?
Answer: Cadcorp
provides a simple utility for checking the number of physical processors
on any machine. This can be downloaded from here (link).
2)
Question: What is the difference between the ASC and GeognoSIS.NET?
Answer: The
ASC is a COM object which contains the SIS engine. When you start
a session on an ASC website, a copy of this object is created and
used to generate map images and provide feature data. It must reside
within the web server application, and clients must be compatible
with COM, which is normally quite restrictive.
GeognoSIS.NET is a SOAP Web Service that contains the SIS engine.
Unlike the ASC, there is a single instance which is running continually.
It has the same functionality as the ASC, but is independent of the
web server application, and can be contacted by any SOAP-compliant
client. This means that GeognoSIS.NET can be used with web servers
that do not use IIS (or even Windows), PHP pages instead of ASP, and
can reside inside a firewall while the web server is outside.
3)
Question: What are Web Mapping Servers (WMS) and Web Feature Servers
(WFS) and how can I use them?
Answer: Web
Mapping Servers and Web Feature Servers are servers that provide map
data in response to a request made to a specific URL. The data required
– overlays, scale, area of interest etc. – is encoded
into the URL in a standard form.
- The WMS provides static images in well known formats
(GIF, JPEG, PNG), regardless of how the underlying data is held.
- The WFS provides vector data for individual map
features, and it would normally be left to a client application
to render them into an image.
The specifications for these are defined by the
Open Geospatial Consortium (OGC). All Cadcorp SIS products can act
a WMS or WFS client, while Map Modeller, GeognoSIS.NET and the ASC
can also act as WMS or WFS servers. Cadcorp SIS products are certified
compliant to the following OGC specifications:
WMS 1.1.1 (Compliant)
WFS 1.0.0 (Compliant)
While the functionality of the WMS and WFS is relatively
restrictive, they are easy and well-known methods for disseminating
map information. Cadcorp’s products can treat the output from
a web server as a map overlay in its own right, allowing data from
various sources to be drawn together while the data sources themselves
remain isolated. The following example shows some practical uses:
To the client application, the three data sources
all act like local files. However, the WFS (1) might be serving up
data over an internal network where it would be impractical for the
client to access the whole data directly. The WMS might be serving
up images from an external data provider, where the provider is unwilling
to offer direct access to the underlying vector data. Also, either
server might also be serving its data to clients built by other vendors.
Cadcorp also provides a free desktop package called Map Browser which
is designed to view and query data served via WMS and WFS specifications,
as well as GML 2.1.2 and Web Map Context XML data sources. Includes
a theme Wizard for theming WFS data and print capability.
A free product, it can be downloaded from (Link)
4)
Question: What options do I have when developing web sites?
Answer:
There are two main categories of GIS web
sites: Thin Client and
Fat Client.
Both may be built using either the ASC or GeognoSIS.NET.
Thin Client
sites generate pages which consist exclusively
of HTML, JavaScript and images, and will be accessible on almost any
browser. The functionality is restricted to operations that require
just a single mouse click to initiate them.
Fat Client
sites generate pages which contain elements
that execute inside the client browser – either Java applets
or .NET Windows Forms applications. These will require a download
(of an appropriate Java Virtual Machine or .NET Framework, respectively)
to the client machine to function, and may restrict the choices of
browser which can use the site – though many browsers will have
the download present already. A much richer functionality can be provided,
for example sticky-hand-pan and digitising polygons.
Cadcorp provides two toolkits for building fat clients: the Java Tools
with the ASC, and the .NET Tools with GeognoSIS.NET. These can be
customised as required.
5)
Question: How can I use GeognoSIS.NET through a firewall?
Answer: GeognoSIS.NET
talks to its clients using port 4326. If a firewall is present between
GeognoSIS.NET and its clients (for example, a web server application
like IIS), it is simply necessary to make sure that this port is open.
6)
Question: How can I convert an ASC application to run on GeognoSIS.NET?
Answer: Cadcorp
can provide, on request, two DLLs and full instructions to convert
an existing ASC application. These contain a COM wrapper object which
makes the GeognoSIS.NET service appear in all respects like an ASC
object. Approximately three lines of code will need to be changed
in the application to make use of this new object instead of the ASC;
the remainder of the application does not change and there will be
no difference in the appearance of the site to the end-user.
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Technical
FAQ's |
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