Developing with QGIS: What’s Possible?

Lutra Consulting

Its internal arrangement

QGIS

Developing with QGIS: What’s Possible?

● QGIS is very modular

● The QGIS you see is a wrapper

around these libraries:

● QgsGui

● QgsAnalysis

● QgsCore

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What are they?

Python Bindings

● Intermediate layer

● Expose functionality to Python

● Allow functionality to be loaded as a

python module

● Advantages of using Python (over C++):

● Quicker to develop (less lines)

● Code is portable

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Developing with QGIS: What’s Possible?

Interaction

Plugins

Developing with QGIS: What’s Possible?

● Plugins can be C++ or

Python

● QgisInterface class

provides 'point of

attachment' for plugins

● Only functionality exposed

via QgisInterface can be

used by plugins

● Functionality of

QgisInterface actually

implemented in QGIS

Application

● Plugins 'attach' here

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Using QgisInterface

Plugins

Developing with QGIS: What’s Possible?

● QgisInterface object facilitates interaction with QGIS through Python:

● Determining layer count

● Loading layers

● Accessing loaded layers

● Accessing features and their geometry

● Etc.

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GUI library example

Plugins

Developing with QGIS: What’s Possible?

● The GUI library provides a number of GUI elements.

● For example the familiar CRS selector:

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Core library example

Plugins

Developing with QGIS: What’s Possible?

● The Core library allows us to work with:

● Layers

● Features

● Geometry

● Projections

● Rendering

● Measurement

● Expression engine

● Snapping

● Spatial indexing

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InaSAFE - Indonesian Scenario Assessment for Emergencies

Example Plugins

Developing with QGIS: What’s Possible?

● A QGIS Plugin that produces realistic natural hazard impact scenarios (e.g. Tsunami).

● Allows for better planning, preparedness and response activities.

● Conceived and initially developed by the Indonesia's National Disaster Management

Agency (BNPB) and the Australian Government.

● Developed by Linfiniti (Tim Sutton)

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Crayfish

Example Plugins

Developing with QGIS: What’s Possible?

● Plugin for displaying time-varying flood model results

● Used to easily communicate flood risk

● Supports a variety of flood model results including TUFLOW and ISIS 2D

● Developed by Lutra Consulting

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Brief demo

Crayfish

Developing with QGIS: What’s Possible?

How, Why and When?

Standalone Applications

Developing with QGIS: What’s Possible?

● What is it?

● Simply a program that uses the

QGIS libraries (just like QGIS!)

● Python or C++

● Why? / When?

● When complete flexibility is

required

● When a plugin on top of all of

QGIS is overkill

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What's possible?

Standalone Applications

Developing with QGIS: What’s Possible?

● Command-line python scripts for automating tasks

● E.g. Using the QGIS Core library to batch-process some shapefiles

● E.g. Extracting and manipulating feature information

● E.g. Batch-printing a number of similar maps

● More complex, graphical applications

● E.g. QGIS Browser

● E.g. A dedicated navigation tool which:

● Reads vector data

● Displays images using the MapCanvas

● Routes between points

● E.g. A dedicated surveying application ...

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IntraMaps Roam - A Data Collection App by Nathan Woodrow, DMS

Example Standalone Applications

Developing with QGIS: What’s Possible?

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Questions?

Developing with QGIS: What’s Possible?