The Plone Conference was held in Naples, Italy this year and, as expected, was a great experience. Like last year in Seattle, we had a PrimaGIS focused sprint where a group of people worked on the next version of PrimaGIS which is based purely on Plone 3.0.
We had a list of sprint topics that people were able to choose from listed at the official sprint page. Below is a breakdown of the sprint activities, what was accomplished and what is still left to do.
One of the biggest changes in the upcoming PrimaGIS version is OpenLayers integration. I had initially planned that OpenLayers would be used as an alternative user interface for PrimaGIS, but after a thorough introduction and discussion with Josh Livni we decided to use OpenLayers as the sole interface to PrimaGIS and retire the old custom one. I believe that this decision will serve us well in the future and the resources of PrimaGIS developers can be put to better use without having to worry about the map UI. The OpenLayers developers seem to be doing an excellent job at that and we’re grateful to use their work.
Currently the OpenLayers view works fine but there is little user configurability. The next step is to refactor the code so that the UI can be configured using user friendly forms and to make it easier for power users to customize the relevant parts. We also want to hook in the more advanced OpenLayers features such as spatial feature editing.
We also implemented TileCache support for PrimaGIS, so that people can easily configure their TileCache servers to improve PrimaGIS performance. Each presentation layer is able to produce a TileCache configuration section that can be copy/pasted to your TileCache configuration file.
Sean Gillies participated remotely and implemented support in PCL for the Python Geo Interface which allowed us to pull in feature data using all geometry types (point, line, polygon) directly into OpenLayers. Thanks Sean!
Big thanks also to Josh Livni for giving a lightning talk on using OpenLayers maps (including examples on FeatureServer and WPServer), for helping me to understand OpenLayers a bit better and working on the actual integration during the sprint!
New layer classes
Partly inspired by the OpenLayers and partly by the changes made to PCL and ZCO we decided to refactor the PrimaGIS layer classes. Previously there were two types of layers: PrimaGISLayer and PrimaGISDataLayer. PrimaGISLayer was used to create a map layer from spatial data from outside of Zope and PrimaGISDataLayer for data from within the ZODB. In either case it was difficult to share layers between multiple maps.
It had always been a goal to get rid of the artificial difference between the layers and data layers and adding support for sharing layers between maps seemed a good idea also.
The new types of layers are: Layer and Presentation Layer. A Layer class is a combination of what PrimaGISLayer and PrimaGISDataLayer used to be. It is used to select the data source where spatial data is acquired and to define the styling of the spatial features. It doesn’t matter whether the data comes from within Zope or not. The difference is that Layers don’t need to be located within Map objects. They can be located anywhere on your site and shared between multiple maps. A map administration may choose to have a folder where all Layers are stored but this is a totally arbitrary choice.
A Presentation Layer is an object that is stored within a Map object and refers to one or many Layer objects. It is tied more tightly into OpenLayers concepts such as a layer type which can be either base, overlay or vector layer. Each presentation layer is available as a Web Map Service (WMS) layer and renderable by OpenLayers. Connecting multiple Layers into a Presentation Layer allows you create composite layers that can be switched on and off as one. Below is a simple diagram that shows how the different objects are tied together.
Buildout for Linux distributions
Alessandro Amici took on the daunting task of refactoring the primagis.buildout into an alternative buildout configuration that can take advantage of installed system libraries. By default, primagis.buildout builds all the required components from scratch which is a process that can more than an hour even on a modern machine.
The new buildout simply assumes that a given set of packages is installed system wide and compiles the rest of the dependencies against those. Currently the buildout provides a list of debian packages that users of Debian based distributions (such as Debian or Ubuntu) should install prior to running the buildout. See README-deb.txt in the buildout source tree for more specific instructions.
Eventhough the new buildout configuration was put together for Debian based distributions it is also usable on other distributions if a similar set of dependency packages are available. Users of other distributions are invited to contribute a list of packages suitable for their distributions.
The implementation of the buildout, which was initially estimated to take less then an hour :), turned out to be much more complicated task due to packaging bugs and differences in libraries between Debian and Ubuntu. We even created a new buildout recipe to help with working with C-libraries which Alessandro released as bopen.recipe.libinc. Users of 64-bit distributions should give the buildout a try since there have been reported problems when compiling some of the dependencies by hand on these systems.
Sune Woeller and Chris Calloway worked together on a new demo product for PrimaGIS called zgeo.primagisdemo. The idea is to provide a similar effect to the createPrimaGISDemo.py script found in the previous versions. However, instead of putting the demo map in PrimaGIS itself, a separate product was created that sets up the map using a GenericSetup profile for content import. This is still work in progress so stay tuned for a release announcement soon!
Once it’s ready you can simply copy to package into your python path and run the GenericSetup import step to get a PrimaGIS demo in your Plone site.
There are still a few items I would like to see in PrimaGIS 0.7.
- Persistent data stores and symbolizers
- Better OWS properties management view
- Spatial index for ZODB data
- Feature inspection
- Feature editing
On most items the work has already been started and some are are a simple matter of hooking into the functionality provided by OpenLayers.
Thanks again for all the people who participated in the sprint! It’s always great to people meet you know from IRC in real life.