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Before you start the tutorial you need to execute the following preparatory steps:
Start Metview 4 with your local command. At the ECMWF you can do it by typing the following command in a terminal window:
Code Block metview -slog &
The optional -slog switch will enable Metview to print detailed logging information to the standard output.- Download this tarfile with the directory containing the tutorial icons (both exercises and solutions) into your Metview environment (~/metview directory).
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| Info |
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Please be aware that this tutorial is strongly dependent on the availability of the selected WMS services and that of the network itself. Therefore it cannot be not guaranteed that the exercises will work for you. Should you experience any WMS service related problems throughout the tutorial, you can still try out the icons provided in the ‘examples’ folder to see how the WMS client is working in Metview. |
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WMS basics
A Web Map Service (WMS) is a standard protocol for serving geo-referenced map images over the internet that are generated by a map server. The specification was developed and first published by the Open Geospatial Consortium (OGC). WMS provides a way for different organisations to share graphical maps over the internet through specially constructed URLs.
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http://www.opengeospatial.org/standards
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Getting started
In this exercise we will build a WMS GetMap request for a Sea Surface Temperature layer from the NASA Earth Observations WMS server and visualise the resulting image in Metview.
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To overlay a WMS map image with any other data just drag the icons representing the data into the plot. There are two icons prepared for you in the folder to try this out: the ‘coastlines_grey’ Coastlines icon and the ‘mslp’ GRIB icon. Simply drag them into the Display Window and see how the plot has been changed.
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Generating a Series of Map Images
In the previous exercise we selected only one date for our Sea Surface Temperature layer. Now we will take a step forward and select multiple dates to generate a series of map images that can be visualised as an animation in Metview. We will continue to work in folder ‘wms_tutorial’.
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Layer name | shortName |
Date part of dimension TIME | date, dataDate, time.dataDate |
Time part of dimension TIME | time, dataTime, time.DataTime |
Date part of dimension DIM_RUN | date, dataDate, time.dataDate |
Date part of dimension DIM_RUN | time, dataTime, time.DataTime |
Dimension DIM_FORECAST | step, stepRange, time.stepRange |
Dimension ELEVATION | level, vertical.level |
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Editing WMS Requests Manually
The WMS client’s user interface offers two WMS request editing modes: an interactive and a plain mode. So far we have used the interactive mode and it provided us with a high-level user interface to set the parameters and build the request automatically whenever it is possible. However, occasionally there might be a need for changing some request parameters manually and this is exactly what the plain editing mode can be used for.
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- In the plain editing mode the GetCapabilities document is not loaded so the client can neither offer the available values for the parameters nor check if the typed-in values are correct at all.
- When you switch from the plain mode to the interactive mode the WMS client always loads the GetCapabilities request and checks each parameter value against the allowed values. It might result in overriding some of your settings defined in the plain editing mode.
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Importing WMS Requests
Imagine a situation when you have an existing WMS request (as a text string) that you would like to visualise in Metview. The easiest way of doing it is to import the request into the WMS client as it will be demonstrated in this exercise.
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- The import functionality is available both in the interactive and the plain editing modes.
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Using the WMS Client in Macros
In this example we will write the macro equivalent of the exercise we solved in Part 2 to visualise our Sea Surface Temperature WMS layer with a Metview macro. We will work in folder 'wms_tutorial' again.
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