FOSS4G Workshop: Working with mesh layer in QGIS

AUGUST 26, 2019 input mergin qgis

We presented a workshop on Mesh layer in QGIS during FOSS4G in Bucharest. Below is step-by-step guide for those who’d like to know more about mesh layers in QGIS.

Introduction

Data for this tutorial can be found here.

In this tutorial, we are going to work with a mesh layer in QGIS. Throughout this tutorial you will learn to:

  • Load a mesh layer

  • Change symbology

  • Working with time

  • Creating time series/cross section plots

  • Export mesh

  • Creating animation

For the purpose of this tutorial, we are going to use the ERA5 dataset from ECMWF:

(the data in the first link should contain what you need to proceed with this tutorial).

Loading mesh in QGIS

Before loading the mesh layer in QGIS, we are going to add the world map as a background layer.

In QGIS, from the Browser panel, browse to the downloaded data > Working with mesh layer > vector_data.gpkg and add world_map layer.

You can change the project background layer to blue to have an image similar to the one below:

To add the mesh layer:

In QGIS, from the Browser panel, browse to the downloaded data > Working with mesh layer and add Hurricane Michael data from Copernicus ECMWF.nc as a mesh layer (not raster).

Depending on your QGIS settings, the CRS setting window might appear. Ensure you assign EPSG:4326 to the mesh layer.

Mesh layer symbology and styling

To change the mesh layer style:

In QGIS, from the layers panel, select the mesh layer and press F7

The layer styling panel will appear on the right of your QGIS window

Within this panel, you can switch on/off quantities, vectors, style the layer and browse through time.

Below, we are going to switch on the wind data and style it:

On the Style panel, click on Symbology tab

  • **Under Settings section, click on the icon in front of 10 metre

    wind to switch on the quantity**

  • Under color ramp section:

    • Set Min to 0

    • Set Max to 20

    • Interpolation to Linear

    • Color ramp to Blues (Inverted)

    • Mode to Equal Interval

    • Classes to 11

You can change the blending mode to Darken and you will see an image similar to the one below:

To style vector component of the wind data:

  • **Under Settings section, click on the arrow icon in front of 10

    metre wind to switch on the vector**

  • Click on the vector settings section:

    • Enable the option for Display Vectors on User Grid

      • X Spacing: 10 px

      • **Y Spacing: 10 px **

    • For Arrow Length, select Scaled to Magnitude

      • Set the Scale by a Factor of 1

Working with time

If your mesh layer has time dimension, you should be able to browse through time using the slider provided under the settings tab:

Note that the time reference does not always parse correctly. To change the time (if you know the correct format and starting date/time):

Click on the setting in front of time

In the new window:

  • Use absolute time

  • Reference date/time: 29.09.2018 04:00:00

Plotting time series and profiles

To plot time series, you will need to install Crayfish plugin from QGIS plugin repository. Once the plugin is installed:

In QGIS, from the main menu > Mesh > Crayfish > Plot

An empty plot appears at the bottom of your QGIS window. To generate time series for multiple points on the map:

Make sure you have the following settings

Layer: Hurricane Michale data from Copernicus ECMWF

Plot: Time series

Group: [current]

And then click on From Map: Point

Hold Ctrl key on your keyboard and click on the locations you want to plot time series:

A series of graphs will be plotted for each point with matching colours.

You can also create long profile (including aggregated long plot) for a specific time step.

Export mesh to vector or raster

To export mesh to a raster or vector, you can use the processing toolbox:

In QGIS, from the main menu > Processing > Toolbox

Under Crayfish algorithm, double click on Rasterize

A new window will appear:

  • For Input mesh layer select Hurricane Michale data from Copernicus ECMWF

  • For Minimum extent click on … and select Use Layer Extent. In the new pop-up, select Hurricane Michale data from Copernicus ECMWF

  • For Map units per pixel, type: 0.500

  • For Dataset group, select 2 metre temperature

  • For Timestep, select 29 days, 6:00:00

  • Click Run

Similarly, you can export your mesh to points or polygon for each time step.

Export to animation

To export to animation, you can set up a print layout template.

Ensure you have selected 10 m wind quantity from the mesh layer properties panel

Right-click on Hurricane Michael data from Copernicus ECMWF and select Export to animation

Set the correct parameters for start time/end time

Set the values for time, legend, title, etc

Set the filename for the animation file

Mesh calculator

Mesh calculator is similar to the Raster calculator with the following added functionalities:

  • Aggregate functions, e.g. calculate maximum values over time

  • Time filter

Try to calculate the maximum precipitation values for Hurricane Michale data from Copernicus ECMWF dataset

Posted by Saber Razmjooei
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