NetCDF - QGis em PDF, Esquemas de Informática

Baixe NetCDF - QGis em PDF e outras Esquemas em PDF para Informática, somente na Docsity!

NetCDF in QGIS tutorial

Gregory Giuliani

University of Geneva -­‐ EnviroSPACE

http://www.unige.ch/envirospace

Geo For All

http://www.geoforall.org

http://www.osgeo.org/ http://icaci.org/

CONTENT

NetCDF in QGIS tutorial by Gregory Giuliani is licensed under a

• Gregory Giuliani – 11/03/
• Displaying a raster layer from a netCDF file
  • Opening a netCDF file in QGIS
  • Display a specific time step
  • Classifying a NetCDF layer
  • Exporting a specific time step in GeoTiff
  • Displaying information on the NetCDF file
• Creating a temperature table at a specific location
  • Value tool
  • gdal2xyz
• Finding temperature difference between two time steps
• Creating a temporal animation
  • Loop Visible Layers
  • Time Manager plugin

Gregory Giuliani – 11/03/

To change the rendering of your data Right-­‐Click on the layer and select Properties. You can change the rendering of your data under the Style tab.

• Render type: Singleband gray
• Load button (under Load min/max values)
• Contrast enhancement: Strech to MinMax
• OK Your data is now visible in a streched gray version.

Gregory Giuliani – 11/03/ Display a specific time step Currently QGIS handles each time slice has a single Band. So if you wish to select a specific time step, you have to select the corresponding band under the Style tab! Another option is to use the NetCDF Browser plugin. To download and install the NetCDF Browser plugin go to: Plugins > Manage and Install Plugins… Search for « netcdf » in the All tab. Select and Install NetCDF Browser.

Gregory Giuliani – 11/03/ Click on Add Selection and all selected layers will be visible in your Table of Content. Classifying a NetCDF layer If you wish to classify one layer with a color ramp, you have to :

1. Right-­‐click on the selected layer > Properties
2. Under Style tab > Render type : select Singleband pseudocolor
3. Click on the Classify button (do not forget to invert the color ramp)
4. OK

Gregory Giuliani – 11/03/ Your layer is now classified with 5 classe and a color ramp. Exporting a specific time step in GeoTiff You can export in GeoTiff a specific time step.

1. Right-­‐Click on the Selected layer
2. Save As…
3. You will be prompted with the following window

Gregory Giuliani – 11/03/

2. Under the Metadata tab > Properties , you can access more detailed information (that can be also displayed using Raster > Miscellaneous > Information )

Gregory Giuliani – 11/03/

Creating a temperature table at a specific location

So far it is not possible to extract a temperature table at a specific location. However, there are two plugins (Value tool, gdal2xyz) that can be useful to retrieve temperatures based on location. Value tool Load the complete NetCDF data set ( Layer > Add Raster Layer… ) Install and launch the Value tool plugin. This is a docket widget that allows you to explore values layers as table or graphs. Click on a specific location (you have the coordinate of the point on the bottom of the plugin window) and you can display values as a table or as a graph. You can select the table (Ctrl + A) and copy/paste the value in an Excel table. gdal 2 xyz The second option is to use the gdal2xyz tool that is available in Processing > Toolbox, under GDAL/OGR > [GDAL] Conversion

Gregory Giuliani – 11/03/

Finding temperature difference between two time steps

Use the NetCDF Browser to extract two layers at different date. Then go to : Raster > Raster Calculator Double click on your first layer, then click on “-­‐“, and finally double-­‐click on the second layer. The expression should look like: "temperatures.nc_time=2000-­‐ 01 -­‐01_band=001@1" -­‐ "temperatures.nc_time=2014-­‐ 01 -­‐01_band=169@169" Give an Output layer name: tempDifferences.tif OK With a color ramp (5 class, inverted), the result will look like:

Gregory Giuliani – 11/03/ You can do the same operation using the Graphical Modeler ( Processing > Graphical modeler ). Inputs: create two Raster Layer and give them a name Algorithms: search for mapcalculator and select the GRASS command r.mapcalculator Double click on it > fill correctly the information (raster layers, Formula) Run the model