The QGIS Green View Index plugin is a powerful tool for measuring the vegetation cover of a given area. It is easy to use and provides valuable information to urban planners, landscape architects and environmentalists. By using the Green View Index plugin, we can improve urban sustainability, track changes in vegetation cover over time and promote the importance of green infrastructure in cities.
We will publish a series of three articles:
1-Green View index concepts and plugin installation (this article)
1- Green View Index concepts: Introduction
The QGIS Green View Index plugin is a tool designed to help ecologists, urban planners and landscape architects measure the vegetation cover of an area. The plugin is available on QGIS, a widely used open source desktop GIS software. Vegetation cover is an important measure of urban sustainability, as it plays a crucial role in improving air quality, reducing the urban heat island effect and providing habitat for wildlife. In this article we will explore how the Green View Index plugin works and how it can be used to improve urban sustainability.
What is the Green View Index?
The Green View Index (GVI) is a measure of the amount of greenery visible from a particular point in a city. It is calculated by measuring the proportion of greenery visible in a circle around a given point. The Green View Index ranges from 0 to 1, with 0 indicating no visible greenery and 1 indicating full greenery coverage.
How does the Green View Index plugin work?
The Green View Index plugin is a QGIS plugin that automates the process of calculating the vegetation index for a given area. The plugin uses Google Sreet View images to calculate the vegetation index for a set of points in a given area. The plugin allows the user to define the number of directions around the point where the vegetation cover is measured and the viewing angles (horizontal, downward, upward) of the green areas that are taken into account in the calculation.
To use the plugin, the user must first download and install the plugin on QGIS. Once installed, the user can select the area of interest and define the parameters of the calculation. The plugin downloads the necessary images from Google Street View and then generates a map showing the GVI for each point in the area of interest.
Applications of the Green View Index plugin
The Green View Index plugin has a wide range of applications in the fields of urban planning, environmental management and landscape architecture. One of the most important applications is the improvement of urban sustainability. By measuring the GVI in different parts of a city, planners can identify areas that lack greenery and take measures to improve the green infrastructure in these areas. This can include planting trees, creating green roofs and installing green walls.
The Green View Index plugin can also be used to track changes in green cover over time. This can help ecologists and city planners to monitor the impact of urban development on green spaces and to take measures to mitigate the negative effects of development.
The GVI calculation in the QGis plugin
For a more detailed description, I invite you to consult the original document by Alexandros Voukenas on the plugin website.
But the basis of GVI is to calculate the ratio of green pixels in an image to the total pixels in the image.
GVI = green pixels/total pixels
It can take values between 0 (no green pixels in the image) to 1 (all pixels in the image are green).
There are therefore two important things to know and/or define to obtain the GVI:
1- How many images to use for a viewpoint?
The following image shows the different possibilities:
Up to 6 different directions can be selected within the 360° around each viewpoint, spaced at 60° intervals. And for each direction you can choose up to three different tilts: horizontal (0°), downwards (-45°) or upwards (45°).
By default, all directions and tilts are used by the plugin, which represents 18 StreetView images for each viewpoint.
The GVI will then be calculated by adding all the green pixels of the 18 images to the sum of all the pixels of the 18 images.
2- How to calculate the number of green pixels?
The algorithm used for this calculation is that of Li et al.
Installing the plugin
In QGis go to the menu Extensions->Install/Manage extensions
As this is an experimental plugin, make sure that in the Settings tab, the Show experimental extensions box is checked, click on Reload repository, then in the All tab, look for Gren View Index
Click on Install.
Once the plugin is installed, you still have to install two libraries needed to run it. In the programs and applications window, search for QGis -> OSGeo4W
Click to open a shell window and type
pip install gpsphoto
Run the command line, then type
pip install scikit-image
and run the command line. Close the shell. The installation is complete.
Prerequisite for use: The StreetView API key
Don’t worry. It’s true that entering the billing information is not without a mixed feeling. But rest assured, there will be no billing for a minimum of 80 days. If you exceed the quota during this period, the download of images will simply be suspended.
After the trial period you can decide if the free quota is enough or if you have to pay for the service. In any case, to test the plugin you can download more than 100,000 images without reaching the free quota.
Overall, to generate a key, you need to follow the following steps:
- Create a Google account
- Create a new project on Google Maps Platform
- Enable billing for this project (a valid credit or debit card is required, but no fees are charged)
- On the Credentials page, create an API key.
Copy and paste the API key into a text file, as you will need to fill it in each time you run the Street View image upload. The plugin does not keep this information in its configuration settings.