QGIS Plugin for Polygons

Polygon editing is an advanced spatial task which requires a sophisticated geometry editor. To facilitate polygon editing a plugin for the Open Source Geographic Information System QGIS is developed which leverages the full editing possibilities of QGIS. It allows the user to add or edit polygons of existing land deals as well as edit the representing point location of a deal. For a full introduction to QGIS see the QGIS online manual.

Installation

QGIS 2.0 or newer

Note

The following instructions are written for QGIS 2.0. If you are using a different version of QGIS, these steps may vary a little.

  • Download QGIS, install it and launch QGIS Desktop.

  • In the Plugins menu, select Manage and Install Plugins... to open the Plugin Manager.

  • In the Plugin Manager, select Settings on the left and Add... a new Plugin repository.

  • Enter a Name (eg. Land Observatory) and the following URL:

    http://www.landobservatory.org/qgis2/plugins/plugins.xml

    Make sure the repository is enabled.

    _images/qgis_plugin_01.png
  • After clicking OK, the Repository is added to your Plugin repositories.

  • In the Plugin Manager, click New on the left and select the Land Observatory Editor 2. Then click on Install plugin.

  • You will see a mesage that the Plugin was installed successfully. You can then close the Plugin Manager.

    _images/qgis_plugin_02.png

If the plugin was installed correctly, you should see the icon of the Land Observatory in the QGIS toolbar.

_images/qgis_plugin_03.png

Older QGIS versions

If you are using an older version of QGIS (older than 2.0), you can use the plugin written for versions 1.x. To install it, follow the instructions above but use the following repository URL:

http://www.landobservatory.org/qgis/plugins/plugins.xml

Warning

The plugin for QGIS versions 1.x is no longer actively developed.

Usage

Before editing

It is important to know, that you can add new polyons only to existing land deals. In case you have a polygon geometry of a land deal, which is not yet in the database, add first a new deal with all required base information to the web platform.

Currently polygons are attached to the following area-aware attributes:

  • “Intended area (ha)”
  • “Contract area (ha)”
  • “Current area in operation (ha)”

Open a web browser and make sure the deal which you want to edit has already the attribute where you want to attach a new geometry or edit an existing one. If this is not the case you can calculate or estimate the area in hectare and add this figure using the web based deal editor.

_images/deal_platform_1.png

Start QGIS and prepare your data and data sources such as Shapefiles, scanned and referenced maps or satellite images.

_images/qgis_opendata.png

Add or edit a new polygon

Click on the editor button LO located in the plugins toolbar to open the polygon editor.

The editor start window opens where you enter your login credentials. As host address use always http://www.landobservatory.org. Now request all deals within the current map extent with Get Activities.

_images/qgis_editor_startwindow.png

A new point layer named Land deals representation points is added to the map canvas. As the name suggests it represents all existing land deals as points similar to the map view on the web platform.

_images/qgis_dealslayer.png

In the next step select exactly one deal to edit using the usual QGIS selection tools.

_images/qgis_selectdeal.png

Click Start editing Activity from the editor window.

_images/qgis_startediting.png

All available information for the selected land deal is requested and loaded in the editor window.

_images/qgis_attributeslist.png

Meanwhile a new polygon layer for each existing area-aware attribute is added to the map canvas.

_images/qgis_polygonlayers.png

Now edit or add new polygons using the usual QGIS editing tools. Use your additional datasources you prepared beforehand. Always properly finish editing with Toggle editing.

Note

If you have already digitized geometries in a GIS layer you can copy and paste the geometry from one layer to another.

_images/qgis_editcurrentarea.png

To upload your changes go back to the editor window and press Submit Activity.

Warning

Do not close the editor window until you get a success message to make sure the upload was successful!

_images/qgis_submitactivity.png

Edit the location of a deal

To edit the representing location of an existing deal, follow the instructions above. But instead of editing one of the polygon layers, start editing the point layer named Land deals representation points. Use the Node Tool to move the point to a new location and finish editing properly with Toggle editing.

_images/qgis_edit_point_location.png