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Testing UMN Mapfiles with QGIS

The Sunday night session of the QGIS hackfest resulted in a new release of the Mapfile Tools plugin.

This QGIS plugin allows you to display an UMN Mapserver mapfile in QGIS without running a Mapserver instance. It depends only on Mapscript (apt-get install python-mapscript on Debian/Ubuntu) and allows you to zoom and pan on the mapfile layer.

In release 0.6, an output window has been added, which shows error messages and detailed layer information. This makes it a convenient tool to test your mapfiles.

qgis-mapfile-tools

QGIS goes 3D

Marco, Matthias and me spent three days at the QGIS hackfest in Wroclaw (pictures). There I got the time to work on the QGIS globe plugin and made a presentation of the current state.

wroclaw

As soon as the threading branch (Martin Dobias’ Google of Summer project) is merged into trunk, the globe should make its way into trunk as well. In the meantime you can compile the QGIS branch from guthub to test the globe. Thanks Vincent for writing step by step build instructions.

Offline editing plugin for QGIS

For data collection, it is a common situation to work with a laptop or a phone offline in the field. Upon returning to the network, the changes need to be synchronized with the master data source, e.g. a PostGIS database. If several persons are working simultaneously on the same datasets, it is difficult to merge the edits by hand, even if people don’t change the same features.

Therefore, Mathias Walker implemented an offline plugin for QGIS. This plugin automates the synchronisation by copying the content of a datasource (usually PostGIS or WFS-T) to a spatialite database and storing the offline edits to dedicated tables. After being connected to the network again, it is possible to apply the offline edits to the master dataset.

To give the plugin a try, unpack the sources, apply the patch ‘qgis_svn.diff’ to a current svn version of QGIS. Then copy the offline_editing folder to $PREFIX/src/plugins and recompile QGIS.

The usage of the plugin is straightforward:

  • Open some vector layers, e.g. from a PostGIS or WFS-T datasource
  • Save the project
  • Press the ‘Convert to offline project’ button and select the layers to save. The content of the layers is saved to spatialite tables.
  • Edit the layers offline
  • After being connected again, upload the changes with the ‘Synchronize’ button

Screenshot

Presumably, the offline editing plugin will be part of the next QGIS version (1.6)

Understanding what’s going on in ExtJS

Recently I had to pre-select a Node inside a TreePanel ExtJS widget. I tried many ways but failed because most of the time when I tried to:

  node.select();

that node would not yet be rendered into the browser’s DOM and so the select would fail somewhere inside the extjs.js blob with something like "this ... undefined ...". What I needed was a "rendered" event, but there doesn’t seem to be such an event for neither TreePanel not TreeNode or any of their superclasses. Diving into ExtJS code was not really very helpful because it’s a framework that does things through layers and layers and as such is not trivial to understand quickly.

Thus, the same ole problem with JavaScript as ever: “show me all the events there are”. However, surprisingly, in contrast to standard JavaScript, ExtJS has an easy standard way to accomplish this:

 
  Ext.util.Observable.capture( myTree, function(event) {                                                                                                        
                                         console.log("got an event in myTree");
                                         console.log(event); });

And quickly I discovered that there indeed is an obscure event that I can, out of alternatives, missuse to do what I want, which is expandnode.

Aparently, after a node is exapanded, all its children are put into the DOM and seem to be manipulable then. Thus:

        /*
         * select node with real_id - this is only called once
         * after the tree is rendered for the first time.
         * After that the listener itself is unregistered.
         */
        function select_node(node) {
          node.eachChild( function(child) { 
            if(child.attributes.real_id == real_id ) {
              child.select();
              categories_panel.un('expandnode', select_node);
            }
          });
        };
        myTree.on('expandnode', select_node);

Tomáš Pospíšek