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Overview

You have seen already how to either visualise your outputs either processed data on the display or saving save it to a file. Most processing you will do with Metview will lead to a visualisation you might want to save, either to either publish it on web pages or in reports, or simply to keep records. This session will give you more information on how you can save and customise your visualisations. 

Output formats

All graphical output formats are generated through ECMWF's graphics library Magics. This means that all graphical capabilities in Metview depends depend on what Magics offers. Detailed descriptions of the output formats and their settings can be found in the Magics reference documentation.

The table below gives you a list of all the formats that Magics/Metview support and how you can use them.

The KML

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output format

KML is a very special output format. It has no notion of output size since it is displayed on the globe. KMZ is the compressed version of the KML files and is written by default. You can write out the uncompressed KML if you want to debug the output.

Metadata

When a large number of plots are generated it is often hard to find later plots with specific contents. What can help is to store additional information with the plots to describe what the content is. These descriptions about the content are called Metadata. Magics/Metview support the saving of such metadata when the format allows this. Especially in text/XML based formats, such as Postscript and SVG, you can use simple UNIX tools like grep to search the files for specific keywords.

How to save your visualisations

Here we quickly recap describe how you can save your display displays from the interactive plot window or save them within Macros.

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Whenever you have a plot window open, you are able to export the plot into other file formats. You can either select the export button in the menu ( option, either from the toolbar button (it looks like a floppy disk with a pen),

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or

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from the File menu. The keyboard shortcut is Ctrl+s

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You will be presented with a dialogue (shown below) similar to what is used by other programs to choose a location and filename for the saved output.You can select which pages you want to save (if you have a series of them), which format and if you want to edit any format-specific options.

If you select the "spanner" icon , you are offered an editor to choose format specific options. The example below shows the options for the KML format.

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Setting output formats in macro code

The following piece of code shows the simplest way to save your plot as a PDF file instead of creating an interactive Display Window.

# set up the output format

 pdf = pdf_output(
      output_name : "my_plot"
)
setoutput(pdf)


data = read("z500.grib")
plot(data)  #  the plot will be sent to the PDF file

Try it!

The pdf_output() function defines how a PDF file should be generated. More options are available to further customise it. The setoutput() function selects this output format. So our code can contain many output format definitions and then select just one (or more) with the setoutput() function at run-time (see later).

You will have already seen some examples of how to save outputs in Macro in previous exercises. The following code example shows how to set multiple output formats at the same time and also set various parameters for the different output formats. Note that in most cases the default values are sufficient. A list of all options can found in the Magics documentation for each format at: PostScript, SVG, PNG and KML.

#
# Setting common output options for multiple formats
#
output_common = ( 
      output_name            : "/tmp/myOutputTest",   # specify relative or full path
      output_width           : 1000,                 # set width in pixel
      output_title           : "Map of Z500",        # title used by a viewer
      output_debug           : "ON",                 # print extra information
)

ps = ps_output(
      output_filelistcommon,
      output_ps_scale  : "ON",     : 0.9,    # scale content to 90%, for  # save list of files generatedsome printers
      output_ps_filelistcolour_name model  : "/tmp/filelist.txtCMYK"   # whereset tocolour savemodel theto listCYMK
)

pspng = pspng_output(
      output_common,
      output_ps_scalewidth           : 0.91000,     # scale content to 90%, for some printers            # set width in pixels
      output_pscairo_colourtransparent_modelbackground : "CMYKON"  # setto colourget modeltransparent to CYMKPNGs
)

pngsvg = pngsvg_output(
      output_common,
      output_cairo_transparent_background : "ON"  # to get transparent PNGs
)

svg = svg_output(
      output_common,width        : 1000,                 # set width in pixels
      output_svg_fix_size : "ON",   # this fixes the size to 'output_width'
      output_svg_meta     : "Metview map of Z500",
      output_svg_desc     : "This file was generated for the Training course"
)

kml = kml_output(
      output_common,
      kml_description : "This file was generated for the Training course",
      kml_author      : "Stephan Siemen",
      kml_link        : "http://www.ecmwf.int",
      kml_latitude    : 30,     # latitude where Google Earth centres the view
      kml_longitude   : 120,    # longitude where Google Earth centres the view
      kml_coastlines  : "ON"    # normally OFF"
)

output_drivers = [ps, png, svg, kml]

setoutput(output_drivers)

data = read("z500.grib")

plot(data)

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# check run mode
mode = runmode()

# select outcome dependent on run-mode
if(mode = "execute")
 then setoutput(to_pngfilepng)
else if (mode = "batch")
 then setoutput(to_psfileps)
else if (mode = "visualise") 
 then print('Plotting to screen')  # for screen do nothing
else if (mode = "prepare")
 then print('Plotting to screen')  # for screen do nothing
else
 fail("Only execute, batch and visualise allowed")
end if

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Create a new Macro icon and rename it outputs. Write a small macro code to read the file z500.grib and visualise plot it on the screen but saves it to a PDF if . If the macro is run in batch mode and saved , the plot should be saved as a PDF file somewhere into /tmp. ; otherwise, plot it to a PNG file.

1. Run the code in the Macro Editor and see what happens if your execute the macro.
2. Go on the command line and change to the directory where the macro is located. Execute the macro from the command line outside Metview.

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Some graphical formats, such as PostScript and PDF, allow multiple pages within the documents. Other formats, such as PNG, will contain a single page at the time and therefore contain a number in their filename to indicate which page they contain. If you plot, for example, a fieldset with 3 fields to a PostScript file,  it will contain 3 pages - each field is plotted into the same view, but on a different page.

You can also trigger a new page in Metview Macro with the function

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This function is normally used within loops to generate output of each iteration on a separate page (or file). It is the only way to use different views on different pages - this is the main purpose of it.

To use newpage() you need first to define a plot_superpage() as shown in the example below.

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dw = plot_superpage(
    pages : [plot_page(),plot_page()]] #  use default page
)

plot(dw[1], ...)
newpage(dw)
 
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plot(dw[2], ...)

Here we create two a default sized pages page with plot_page(), which attach attaches to the super page. Than we assign each plot command to a page.

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Take the macro from the previous task and add a page where you visualise the same field but over Europe only.modify it to produce a 2-page output: the first page should be on a default Geographic View, the second should be over Europe only. Only plot the first field in the data. The result should be 2 PNG files or a 2-page PDF, depending on how you run the macro.

Further processing outside Metview

Of course you can do further processing of plots outside Metview. The page Generating animated GIFs from Metview plots gives you some helpful advice if you want to build animations.

Metview/Magics also supports special tags in SVG for the Inkscape graphical editor. This open source editor is great for when you need to further annotate your maps.

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If you have extra time

If you have time, you might want to try out opening your SVG file from the first exercise above in inkscape and alter it and save it to a PNG.

Using Web Map Services (WMS)

Metview provides a module to request maps from a Web Map Services (WMS). The WMS standard is defined by the Open Geospatial Consortium (OGC), which is very popular in the GIS community. The WMS module can be used to query an OGC-compliant WMS server, retrieve maps from it and overlay them with other data. The WMS icon is a great way to integrate web services within Metview. 

We have a separate tutorial which shows in more detail how you can use maps served by web map services within Metview.

Tasks

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