Plotting Satellite Images with Python and Diana

This document aims to show how to use Diana to create plots of satellite images from Python scripts and from within the ipython notebook.

Installation

To get access to the Python modules that expose Diana's plotting features, you need to install the python-diana package from the local package repository. Either use the package manager to do this, or enter the following in a terminal:

apt-get install python-diana

Some examples can also be found in the python-diana-examples package.

Importing Modules

You can use Diana's functionality from Python by importing the bdiana and plotcommands modules from the metno package. If you are using an old version of ipython (earlier than version 1.0) then it is also useful to import the embed function from the metno.ipython_extensions module.



In [1]:

    
# Import the modules needed to use Diana.
from metno import bdiana, plotcommands
# Import an extension that lets us embed an image into a worksheet.
from metno.ipython_extensions import embed

Initialisation and Setup

The bdiana module contains the BDiana class. This provides a convenient interface to Diana's functions and also wraps several initialisation steps into one object. To start using Diana, we simply create an instance of this class.



In [2]:

    
b = bdiana.BDiana()

By default, Diana doesn't know anything about data files or other resources. The locations of data files, definitions of plot types, palettes, and other pieces of information are stored in one or more setup files. We choose one of these and use the setup method to let Diana know where to get data from.



In [3]:

    
b.setup("/etc/diana/setup/diana.setup-COMMON")

The method will return True if the setup file was loaded correctly.

Reading Satellite Image Information

With the setup file loaded, we can ask for information about satellite images known to Diana.



In [4]:

    
products = b.getSatProducts()

The dictionary obtained contains information about the satellite products available. The dictionary keys contain the product names. The values are also dictionaries.



In [5]:

    
keys = products.keys()
keys.sort()
keys

Choosing one of these, we obtain a dictionary containing information about the subproducts.



In [6]:

    
products["NOAA"]

We obtain the dictionary value that corresponds to the subproduct we are interested in and read its channel attribute to get the list of available channels.



In [7]:

    
channels = products["NOAA"]["N-Europa"].channel
channels

The times for which there are images can be found by querying the BDiana object with the product and subproduct names.



In [8]:

    
times = b.getSatTimes("NOAA", "N-Europa")
times[-5:]

Plotting a Satellite Image

We create a plot command for the satellite data, using the alpha option to make the image partially transparent.



In [9]:

    
s = plotcommands.Satellite()
s.setOption("product", "NOAA")
s.setOption("subproduct", "N-Europa")
s.setOption("channel", "day_night")
s.setOption("alpha", 64) # 0-255

We create a plot as usual by creating plot commands for the area and map, as well as for the satellite data.



In [10]:

    
a = plotcommands.Area(name="Atlant")
m = plotcommands.Map(map="Gshhs-Auto", backcolour="white", land="on")
m.setOption("land.colour", "flesh")
l = plotcommands.Label(data="")

b.setPlotCommands([a.text(), m.text(), s.text(), l.text()])
b.setPlotTime(times[-1])
embed(b.plotImage(500, 500))

We can obtain a mosaic of images by setting the mosaic plot option.



In [11]:

    
s.setOption("mosaic", 1)

b.setPlotCommands([a.text(), m.text(), s.text(), l.text()])
b.setPlotTime(times[-1])
embed(b.plotImage(500, 500))

Plotting a Radar Image

Radar images are obtained and plotted in the same way as satellite images. We obtain information about the images from the same dictionary of products.



In [12]:

    
products["YR-RADAR"]["WR_NORDICLCC"].channel

We use the Radar plot command, but this is effectively the same as the Satellite plot command. The string passed to Diana contains a command to display a satellite image.



In [13]:

    
r = plotcommands.Radar()
r.setOption("product", "YR-RADAR")
r.setOption("subproduct", "WR_NORDICLCC")
r.setOption("channel", "PSC_Z")
r.setOption("alpha", 64) # 0-255

a = plotcommands.Area(name="Norge")
b.setPlotCommands([a.text(), m.text(), r.text(), l.text()])
b.setPlotTime(times[-1])
embed(b.plotImage(500, 500))