Feeds

Back to basics for SQL Server 2008

Hand feeding

The essential guide to IT transformation

However there is an important distinction between data collection and storage. Tools like MapPoint return values with N,S,E,W notation, so it was easier for our human convertors if we collected the data in that format. The subsequent conversion to the signed format that SQL Server requires is, of course, trivial:

 


SELECT 
foo,
        (CASE WHEN LatNS = 'S' THEN -1 ELSE 1 END) * Lat AS Latitude,
        (CASE WHEN LongEW = 'W' THEN -1 ELSE 1 END) * Long AS Longitude 
FROM penguin;

Many people felt that we should write our own spatial data types, for example good old Anonymous Coward felt moved to say:

"I am quite frankly incredulous that you have to wait for a new OS and new database design to do this, why not just define a special data type: latitude, longitude, date. Any competent final year computing science graduate could do as much."

We can clearly store spatial data as a pairs of signed values -1.222, 53.327, so why not roll our own data types? One answer is that spatial data isn't just about storing points in isolation. We store it so that we can answer questions like: "Are these points inside this polygon?" We'd need to store the polygon and the obvious place to put it is inside the data type that inevitably makes the internal structure of the data type more complex. This internal structure, combined with a complex model of the Earth's shape, makes indexing essential but non-trivial.

Another answer lies in the functions/methods associated with the data type. Most engines that support spatial data types provide a wide range of these - something in the order of 70. They provide the facility to, for example, translate from Well Known Text (WKT), return the distance between two points, return true if a point is inside a polygon and so on.

So, can you write your own, spatial data types complete with non-spherical modeling, indexing and an appropriate set of methods? Of course. You can write your own RDBMS as well... it's just a matter of how much time you have and what you charge per hour for your time. For most people, us included, it is not a realistic option unless the spatial requirements are relatively simple.

Which brings us very neatly to the next question: how do we import data that is stored as signed values into the spatial data type?

In SQL Server 2008 the answer is that we use one of those built-in methods.


UPDATE
        tblSpatialData
SET
        SpatialLocation = 
                geography::STGeomFromText('POINT (' + 
                        CONVERT(nvarchar, Latitude) +
                        ' ' +
                        CONVERT(nvarchar, Longitude) +
                        ')', 4326)
WHERE
        Latitude IS NOT NULL
AND Longitude IS NOT NULL

So the next (rhetorical) question is, how does it work? What is that 4326 doing?®

Follow Register Developer regular Mark Whitehorn next time on Project Watch: Microsoft 2008 as he continues to roll out a spanking-new 1TB database for several thousand users on Microsoft’s SQL Server 2008, Visual Studio 2008 and Windows Server 2008.

Boost IT visibility and business value

More from The Register

next story
Munich considers dumping Linux for ... GULP ... Windows!
Give a penguinista a hug, the Outlook's not good for open source's poster child
The Return of BSOD: Does ANYONE trust Microsoft patches?
Sysadmins, you're either fighting fires or seen as incompetents now
Intel's Raspberry Pi rival Galileo can now run Windows
Behold the Internet of Things. Wintel Things
Microsoft cries UNINSTALL in the wake of Blue Screens of Death™
Cache crash causes contained choloric calamity
Eat up Martha! Microsoft slings handwriting recog into OneNote on Android
Freehand input on non-Windows kit for the first time
Linux kernel devs made to finger their dongles before contributing code
Two-factor auth enabled for Kernel.org repositories
prev story

Whitepapers

5 things you didn’t know about cloud backup
IT departments are embracing cloud backup, but there’s a lot you need to know before choosing a service provider. Learn all the critical things you need to know.
Implementing global e-invoicing with guaranteed legal certainty
Explaining the role local tax compliance plays in successful supply chain management and e-business and how leading global brands are addressing this.
Build a business case: developing custom apps
Learn how to maximize the value of custom applications by accelerating and simplifying their development.
Rethinking backup and recovery in the modern data center
Combining intelligence, operational analytics, and automation to enable efficient, data-driven IT organizations using the HP ABR approach.
Next gen security for virtualised datacentres
Legacy security solutions are inefficient due to the architectural differences between physical and virtual environments.