.. comment out this Section (by putting '|updatedisclaimer|' on top) if file is not uptodate with release

.. _diagram_overlay:

Diagram Overlay Plugin
======================

|diagram| The :guilabel:`Diagram Overlay` Plugin allows you to add a graphic
overlay to a vector layer (see figure_overlay_1_). It provides additional and
not yet implemented features to the :guilabel:`Diagrams` tab, described in secion
:ref:`sec_diagram`.

Before starting, the :guilabel:`Diagram Overlay` Plugin needs to be activated
using the Plugin Manager (see Section :ref:`load_core_plugin`). It will then
appear as :guilabel:`Overlay` tab in the :guilabel:`Layer Properties` dialog
next to the :guilabel:`Diagrams` tab.

.. _figure_overlay_1:

.. only:: html

   **Figure Overlay 1:**

.. figure:: /static/user_manual/plugins/overlay_tab1.png
   :width: 25em
   :align: center

   Vector properties dialog with overlay tab |nix|

The :guilabel:`Overlay` tab provides support for Pie charts, Bar charts and
proportional SVG symbols.

Similar to the :guilabel:`Diagrams` tab, we will demonstrate an example and
overlay the alaska boundary layer a piechart diagram showing some temperature
data from a climate vector layer. Both vector layers are part of the |qg|
sample dataset (see Section :ref:`label_sampledata`).

#. First click on the |mActionAddOgrLayer| :sup:`Load Vector` icon, browse to
   the |qg| sample dataset folder and load the two vector shape layers
   :file:`alaska.shp` and :file:`climate.shp`.
#. Double click the ``climate`` layer in the map legend to open the
   :guilabel:`Layer Properties` dialog.
#. Click on the :guilabel:`Overlay` tab, activate |checkbox| :guilabel:`Display
   diagrams` and select 'Pie Chart' from :guilabel:`Diagram type` |selectstring|
   combobox.
#. We want to display the values of the three columns ``T_F_JAN``, ``T_F_JUL``
   and ``T_F_MEAN``. First select ``T_F_JAN`` as Attributes and click the
   **[Add]** button, then ``T_F_JUL`` and finally ``T_F_MEAN``.
#. Diagram size is based on linear scaling of a classification attribute. We
   choose ``T_F_JUL``, click on **[Find maximum value]** and set size to ``20``
   and :guilabel:`Size unit` |selectstring| to 'Millimeter'.
#. Now click **[Apply]** to display the diagram in the |qg| main window.
#. You can now adapt the chart size, or change the attribute colors double
   clicking on the color values in the attribute field. Figure_overlay_2_
   gives an impression.
#. Finally click **[Ok]**.

.. _figure_overlay_2:

.. only:: html

   **Figure Overlay 2:**

.. figure:: /static/user_manual/plugins/overlay_tab2.png
   :width: 25em
   :align: center

   Pie chart diagram from temperature data overlayed on a map |nix|

Additionally in the :menuselection:`Settings --> Options` dialog, there is a
``Overlay`` tab where it is possible to select the placement algorithm of the
diagrams. The 'Central point' method is a generic one, the others use algorithms
of the PAL library. They also consider diagram objects and labels in different
layers.