The “Geohype” of the last years has lead to an increasing distribution of so called “Earth Viewers”. Microsoft Virtual Earth with its rich content and highly interactive user interface is certainly one of the most successful services of this type. However, there are scenarios where you want to achieve more than these services provide out of the box. The combination with spatial-enabled databases is a natural fit since it allows analysing and aggregation of the data directly in the database and transporting just the result of this process to the presentation layer. This series of blog-postings gives a brief introduction in the spatial infrastructure of SQL Server 2008 and discusses how we can integrate with Virtual Earth. It is not meant to be a complete overview about the possibilities but rather an introduction into the technical approach.
For those of us who have been engaged in the geospatial business it is not really a surprise that the geospatial applications have become increasingly popular. In the 22nd of January 2004 issue of Nature you even found that “the US Department of Labour identified geotechnology as one of the three most important emerging and evolving fields, along with nanotechnology and biotechnology” and that the market for these type of applications is about to explode. Well, we have heard these kinds of expectations before but with the advent of the so called “Earth Viewers” there was a true breakthrough which created a geohype and maneuvered geotechnology into the mainstream.
While it can be very simple to create these kinds of applications there is the still quite often the need to integrate with traditional GIS or spatial-enabled databases. Earth Viewers combine ease of use with attractive content and a rich user experience but by themselves they have limited functionality when it comes to data creation, data storage or spatial-relationship queries; thus it is a natural fit to combine the Earth Viewers with spatial-enabled databases and GIS.
In this series of blog-postings we will discuss the integration of Microsoft SQL Server 2008 with Microsoft Virtual Earth and we will briefly discuss how to use ETL (Extract, Transform and Load) tools to load the data into Microsoft SQL Server 2008 in the first place and to perform basic transformations
Some Mapping Basics
If you are a geospatial specialist this is nothing new for you but if you are more a database administrator or a web developer this might be a new concept for you so let’s step back and have a look at background.
The world is a 3-dimensional object while a screen or a piece of paper is a flat object. SQL Server 2008 can work with both concepts and so can Virtual Earth if we use it in both 2D and 3D-mode. However, if we use the 2D-mode we need to use a so called projection to get from 3 to 2 dimensions. Virtual Earth uses the Mercator-projection which is a cylindrical projection. There are many advantages in this projection but the downside is that a cylindrical projection becomes less accurate the closer you get to the poles. Thus you will only be able to work accurate between 85 degrees North and 85 degrees South.
There are a large number of coordinate-systems in use; many countries have specific coordinate-systems like the OSGB36 (Ordnance Survey Great Britain 1936) and some are even specific for a single infrastructure like a manufacturing facility or a steelworks.
However, when you need a coordinate system which is available in any place on the world you are usually looking at a geodetic coordinate system such as the WGS84 (World Geodetic System 1984). This coordinate system was originally introduced to reference locations acquired by the Global Positioning System (GPS).