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You will create some icons yourself, but some are supplied for you . Please so please copy them from the command line with this command:
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cp -R /home/graphics/cgx/tutorials/wms_tutorial $HOME/metview |
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In this exercise we will learn about the ODB Database icon and see how to examine its meta-data content.
The ODB Database Icon
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Open folder 'database' inside your 'odb_tutorial_4.1' folder (double-click or right-click, edit). Here you will find all the ODB Database icons used in the tutorial.
These icons represent ODB databases residing on our file system. More precisely, in our case, these are only symbolic links to the databases to save disk space. Symbolic links can be really useful for working with the usually quite large ODB databases.
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To create a symbolic link right-click in the Metview desktop with no icons selected and choose Create new ... from the menu. Please note that the text label under symbolic link icons is in italics. |
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| Warning |
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ODB database icons, like any other Metview icons, can be dragged and dropped between Metview folders. However, if the icon is not a symbolic link the whole data structure, which is usually very big, is copied/moved over during such an operation, so it might take a significant amount of time. On the contrary, for a symbolic link the link itself is copied over during a drag and drop operation so it is safe to use. |
The ODB Binary Representations
In the framework of the Observation Handling and Monitoring project a new binary representation was developed for ODB to enable MARS archiving. This new format is referred to as ODB-2, while the previous one as ODB-1. The ODB-2 format currently comes only with ODB has two binary representations: there is the current format (ODB) which has a "flat" structure (i.e. with one single table) and represented by a single file instead of the usual CCMA/ECMA, etc. directory structures.
, an the older hierarchical format (ODB-1) which is stored in a directory structure instead of a single file. Metview uses the same icon for both ODB formats, hiding the differences between them and providing the users with an interface which is format-transparent. However, please note that wind plotting presently requires different approaches for the ODB -1 and ODB-2 1 formats, respectively (see Part 3 and Part 7 for details on the differences).
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Right-click on your 'CCMA.obs' ODB Database icon and select examine from the icon menu. This will start the ODB Examiner application that displays the meta-data of the database. By default you should see the Tables tab of the interface showing the ODB table hierarchy. This hierarchy only exists only for the ODB-1 format (so we can see that our 'CCMA.obs' icon represents an ODB-1 database). By clicking on a table name the columns belonging to the selected table are displayed in the right hand side of the interface. There are two more tabs in the interface: the Columns tab showing the list of all the available columns and the SET Variables tab providing the users with the list of pre-defined ODB variables. Explore these tabs and then close the ODB Examiner.
Now right click and examine icon 'AMSUA.odb'. It points to an ODB -2 database (just like icon 'AIREP.odb'). Since there is no table hierarchy to be shown the list of all the available columns is displayed by default (Columns tab).
The data values stored in the ODB can be also inspected in the ODB Examiner (this feature is currently working only does not work for ODB-21). Just click on the Data tab to see the data values. If there are too many values to be shown the ODB Examiner displays the data items in blocks. The actual size of the data blocks (in terms of rows) can be seen at the bottom of the interface next to the data block navigation buttons. Data blocks were introduced to reduce memory usage since the ODB Examiner has to keep in memory all the values shown in the Data tab.
Remarks
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Each column in the Data tab can be sorted by clicking on the column heading. However, please note that sorting is enabled only if all the available data values can be displayed at once, i.e. no data blocks are to be used. By default the ODB Examiner starts splitting the data into data blocks if more than 60 MB is needed to store the data values in memory. You can override this default value in the Configure dialog available from the Settings menu in the menu bar.
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Symbol Plotting on Maps
In this exercise we will retrieve and plot the brightness temperature values for channel 5 from our 'AMSUA.odb' database. Please open folder 'tb' inside folder 'odb_tutorial_4.1' to start the work.
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