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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MapServer+Windows 64 bit+Apache=Crash?

Mar 112010

I developed my MapServer application on Windows 2003 (a virtual 64 bit server running), using MS4W (MapServer for Windows), and had set up TileCache, and some Python scripts to run through Apache. I had managed to crash the set up numerous times in development, but I hadn’t come across any errors not of my own making.

The installation went well  on the production server which was also a 64 bit machine, but was using Windows Server 2008. The site had an unpublicised release as it is still in beta, and from this was getting about 60 – 70 visitors a day.

I use host-tracker.com – a web site monitoring service which lets me know if a site is down, and I was soon made aware that it was.. There were no responses at all coming from Apache, even though the Apache service was still running. Not even HTML pages were returned. Restarting Apache returned the service to normal, but this was happening every other day.

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Web Mapping Services & Security

Jan 202010

For the majority of public GIS systems I’ve worked on all the data in a database is available to users via the mapping interface. If someone wanted to hack in and “steal” data the only concern would be the bandwidth they took up. Security for these systems is fairly low down on the list of priorities, if it’s on the list at all.

GIS systems with organisational data are often only accessible (in theory) through an Intranet, so if the network is well protected then so isthe GIS.

There have only been a few mapping systems I’ve worked on where there is a mix of public data and datasets with restrictive access in the same database. The location of rare bird species (people will go to some lengths for a rare egg) and hallucinogenic mushrooms in a Biodiversity GIS being an example.

I’m currenty designing a MapServer system that will serve out WMS layers to the public, and a few which are limited to certain IP address ranges. WMS and security was something I had never previously investigated. The rest of this post outlines the current situation, and an attempt to restrict WMS access on my server.

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Running Python through Apache

Jan 182010

I’m trying (and having) to start using Python more and more due to its ubiquity in the OpenSource GIS world. There are a number of add-ons and libraries for MapServer that require Python to function properly and/or quickly. It is also widely used for scripting both MapServer objects and for raster manipulation using GDAL. I initially set up Python under Apache to run the Tilecache tile server.

According to the ModPython site – “Python will run many times faster than traditional CGI and will have access to advanced features such as ability to retain database connections.”

Mod_python is an Apache module that embeds the Python interpreter within the server, and can be downloaded from their site. There are versions for both Unix and Windows, which makes it ideal for MapServer for Windows (MS4W). Ironically after saying that using Python for web applications is many times faster than CGI, the ModPython download page uses CGI..

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WMS GetCapabilities

Jan 162010

Yes, I’d like to see the map layers and capabilities available from my MapServer MAP file, and no I don’t want to download mapserv.exe..

Messing with Headers

I had the same problem with both Firefox and Internet Explorer 7 each time I issues a request such as:

http://localhost/cgi-bin/mapserv.exe?map=/ms4w/apps/my.map&SERVICE=WMS&VERSION=1.1.1&REQUEST=GetCapabilities

The browser tried to download mapserv.exe. The “exe” did actually contain the GetCapabilities XML, but it is very annoying to have to manually open it in another program each time.

This is a FAQ on the MapServer site which suggested that a program needs to be manually associated with the MIME type returned by the requests – application/vnd.ogc.wms_xml.

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Map Server Expression Errors

Jan 072010

Errors…

After turning on logging to diagnose an issue with MapServer I found a more worrying error, that was causing the log file to fill up at a rate of about 2MB a minute! I was reusing a legend for five or six datasets, and it was causing the following debug notes:

[Thu Jan 07 15:28:21 2010].629000 msyyparse():
Expression parser error. syntax error

[Thu Jan 07 15:28:21 2010].629000 msEvalExpression:
Expression parser error.
Failed to parse expression:  ( >= 2.251) AND ( <= 2.5)

Map Server Logging

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MapServer and SQL Server 2008 Plug-in

Dec 182009

The SQL Server 2008 plugin for MapServer is a “native driver modeled on the PostGIS driver to mapserversupport SQL Server 2008’s newly added spatial capabilities.” It works fine for displaying data as WMS layers in OpenLayers however I ran into all sorts of problems when trying to use the GetFeatureInfo WMS query.

With MapServer 5.2.1  (installed using MapServer for Windows – MS4W v2.3.1) no error message was returned, however neither was any data . I initially thought this was due to the following bug in the plugin, which was reported to have been fixed for MapServer 5.4.

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