OGR Comes to SQL Server 2008 Spatial

Sep 252010

image OGR, created by Frank Warmerdam, is an open source library and set of command line utilities for reading and writing geospatial vector data using many different formats . It is the vector equivalent of GDAL which has similar functionality for rasters.

The name of the library is a vestige from when OGR used to stand for OpenGIS Simple Features Reference Implementation. However as OGR is not fully compliant with the OpenGIS Simple Feature specification the name was changed to OGR Simple Features Library (from the GDAL FAQ).

The latest additions to the OGR formats are the SQL Server 2008 geometry and geography. This enables spatial data in SQL Server 2008 to be reprojected, and converted to other formats (shapefiles, MapInfo, KML, GML, GeoJSON and any of the many other formats already supported by OGR) using freely available open source tools. Details on the associated OGR tools can be seen here.

The full MSSQLSpatial OGR driver notes and details are available online.

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64-bit Mapscript for Python on Windows

Aug 032010

Tamas Szekeres maintains a site with many different compiled versions of MapServer at http://vbkto.dyndns.org/sdk/ (the site can occasionally be overloaded or down). These are compiled daily direct from the source. It is a veritable Aladdin’s cave of treasures – especially if you are installing on a Windows Server, and even more so if you are installing for 64bit.

It gets even better though! Included in the installation are the latest SQL Server 2008 driver, 64 bit GDAL, and MapScript Python bindings. MapScript allows MapServer functions and classes to be scripted in a variety of languages.

As Python is becoming ubiquitous in the GIS world (opensource and proprietary), if you aren’t familiar with PHP then You can download the zip file and extract to a folder on your machine, in the example below I used C:\ms4w64 (old habits die hard!).

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Setting up a Secure Cascading WMS on MapServer

Jul 202010

image There a number of benefits to using a cascading WMS service – a WMS service that is read and then forwarded on through an intermediary WMS server:

  • you can cache the service (for example with TileCache) to greatly improve performance
  • your application need only worry about a single point of connection, using WMS layers aggregated from many different sources
  • you can add additional metadata missing from the source
  • services can be reprojected (using GDAL)
  • you can merge WMS layers together and server them out as a new map layer

There are also some negatives:

  • you have additional server configuration to set up and maintain
  • if you are not adding or changing the WMS service you should probably connect to the WMS service directly in the client applications, otherwise there will be a performance hit
  • caching may contravene the licensing agreement of the original WMS source

The rest of this post details the steps in setting up a cascading WMS using MapServer. You need MapServer 5.4.1 or higher to implement a secure cascaded WMS service. This example uses a 64-bit version of MapServer 5.6 taken from Tamas Szekeres’s autobuilds site installed in a C:\ms4w64 folder. It also assumes MapServer has been configured with SSL as detailed in another post. In this example I use IIS and Windows Server 2003.

64 bit cURL with OpenSSL on Windows

Jul 092010

imageMapServer makes use of libcurl.dll to connect to web resources. The reason I’ve had to learn this is because libcurl.dll is vital when using MapServer as a WMS client, or “a cascading WMS server” – using MapServer to connect to another WMS server and then “forward” them as if they were any other map layer.

libcurl.dll is the library version of the command line tool cURL – a tool written in C (hence the name) that:

is a command line tool for transferring data with URL syntax, supporting FTP, FTPS, HTTP, HTTPS…curl supports SSL certificates, HTTP POST, HTTP PUT, FTP uploading…

..libcurl is most probably the most portable, most powerful and most often used C-based multi-platform file transfer library on this planet – be it open source or commercial. – http://curl.haxx.se/

GIS Servers and the 64-bit Question

Jul 062010

imageThe following is the first in a series of posts related to configuring a 64-bit Windows server as a GIS server  using MapServer and Python.

Why move to 64-bit?

If a server’s operating system and hardware are 64-bit it seems a waste not to take advantage of them. It may be better to look at the question why move to 64-bit software, as why wouldn’t you move to 64-bit software?

Its nice to be able to claim one-upmanship over commercial GIS products who are only now bringing out 64 bit versions. However having gone through the pain of setting up Open Source GIS applications on Windows I’m not surprised companies took the time to simplify the process (and wait for Microsoft to do some of the legwork) rather than dealing with all the 32/64 bit support issues too early.

Using TileCache on IIS

Jul 042010

imageI’ve previously written about using PyISAPie to run Python under IIS – this allows Python scripts to run faster than using CGI. Rather than starting up the Python interpreter each time a request is made to the web server, PyISAPIe starts the interpreter once and only needs to run the script at each request.

TileCache provides a Python-based WMS-C/TMS server – this is allows you create a local disk-based cache of any WMS server (in my case MapServer), and then connect to it through a WMS-C client such as OpenLayers. Using a cache means that rather than have MapServer create an image for every single request for a tile, the first time a tile is requested the image is saved in a folder on the server. On all subsequent requests for the same data TileCache can retrieve this file without needing MapServer. Performance increase is incredible – however watch out for filling up disk space, and remember to empty the cache if you change symbology or update your data.

As mod_python is now officially dead (and has been moved in Apache’s attic), it is yet another reason if you are using Windows servers to run everything through IIS rather than the rather clumsy Apache on Windows. Why pay for Windows, and then install a web server port, thereby losing all the tools, security, and utilities within Windows to manage and administer the web server?

The aim of this post is to describe the set up of TileCache, running through IIS. Continue reading »

OpenSource Upgrades

Jun 242010

image Moving to new versions in OpenSource has in the past been like playing Russian roulette. Just now clicking on “Upgrade to WordPress 3.0″ I thought would lead to a greater understanding of the database schema, template inconsistencies, and plug-in idiosynchrocies of WordPress as I met an inevitable “Upgrade Failed. Please see log for details” message.

But no! Five seconds later, all was successful, and everything looked as before. There have been numerous bug fixes and improvements, but after a brief look through the list I didn’t see any “killer” new features.

In the world of GIS however there are a number of important new versions coming up this summer.

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