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The 'ret_temp' MARS Retrieval icon is already prepared for you to fetch Land TEMP ODB data from MARS fro for a given date. Edit the icon (right-click & edit) and to see what parameters are set. The most important ones are as follows:
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Close the icon editor and perform the data retrieval by choosing execute from the icon's context menu. The icon name should turn orange whilst the retrieval takes place, then green to indicate success. The data is now cached locally. To see what was retrieved, right-click examine the icon. This brings up Metview's ODB Examiner tool. Here we you can see the metadata (Columns tab) and the actual data values themselves as well (Data tab). Close the ODB Examiner.
To save the ODB data from the cache to disk, right-click Save result on the Mars Retrieval icon and save as 'temp.odb'. A few seconds later an ODB Database icon with the given name will appear in at the bottom of your folder.
Using the ODB Visualiser
We will visualise the 500 hPa temperature values from this our ODB using the 'vis_temp' ODB Visualiser icon. The query we need to perform is as follows:
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Right-click visualise the icon to generate the plot. Then drag the the provided Symbol Plotting, Coastlines, Legend and Text Plotting icons into the plot for further customisation. Having done so you should see something like this.
Inspecting the Data Values in the Plot
Data values at the cursor position can be inspected with the Cursor Data Tool, which can be activated by pressing on the gun-sight 
icon in the toolbar of the Display Window. The Cursor Data Tool displays the co-ordinates of the current cursor position and the information for the nearest data point to this position.
You may find hard to use the Cursor Data Tool in data dense regions. To overcome it this launch the Magnifier by pressing on with the magnifier 
icon in the toolbar and navigate move it to your area of interest in the plot. . The magnifying glass can be moved and resized using the mouse, and the magnification scale on its left-hand side can also be adjusted.
Enable the sidebar of the Display Window with the 
button and select the Data tab then the Metadata panel inside it (and select the 'vis_temp' layer at the top if it is not yet selected). You will see . Now select the Metadata panel inside the tab. Here you will find some statistics about the data you plotted and a histogram as well.
Now switch to the Values panel. This features a list showing all the plotted data. In the bottom-left corner click on the
button to activate the Data probe (this will appear in the plot). The probe is synchronised with the list. Try to drag it around in the plot, or change its position through the list. The Magnifier might help you position the Data probe more accurately.
Writing a Macro
We will write a Macro to produce reproduce the same temperature map as we plotted with icons.
Create a new Macro icon (in an empty area of the desktop right-click and select Create new macro) and edit it. First, drag your 'vis_temp' ODB Visualiser icon into the Macro editor just below the line containing the #Metview macroMacro text. Next, drag your 'symbol' Symbol Plotting icon into the editor after below the text the editor already holds. Next, add the following line to the macro:
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A more advanced version of this macro is provided for you in as 'plot_map.mv'. It uses features all the icons we used to customise the original plot, allows selecting the pressure level to plot and automatically adjusts the symbol plotting to to current value range.
Overlaying with GRIB data
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Re-visualise the 500 hPa temperature ODB data with the ' vis_temp' and other icons as you did beforeand drag the Symbol Plotting, Coastlines, Legend and Text Plotting icons into the plot again. To overlay the 500 hPa temperature forecast we need to filter the matching filed from the GRIB file. We will use the The 't500_fc' GRIB Filter icon that is already already set up for to perform this task. Just drag it into the plot, then drag the 't_cont' Contouring icon into the plot as well to customise the contour lines.
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The 'diff.mv' Macro computes the difference between the forecasts stored in the 'fc.grib' GRIB file and the observations stored in the 'temp.odb' ODB. This is achieved by using the following steps:
- the ODB query is performed and the resulting data is converted into Geopoints (this is Metview's own format to stored store scattered geospatial data)
- the matching GRIB filed is read and interpolated to the observation points
- the difference is computed between forecast and observation
Edit it 'diff.mv' Macro and visualise it using the play button. You should see now a difference plot. Try Try to set a different level/parameter at the top of the macro code.
Wind plotting
The 'plot_wind.mv' Macro plots wind on a given pressure level from the 'temp.odb' ODB. It is not a trivial task because the u and v wind components cannot be retrieved from our ODB in a single query. The macro overcomes this difficulty by using the following steps:
- two ODB queries are performed: one for the u and one for the v wind component
- the resulting data is converted into Geopoints
- the macro plots the wind data as Geopoints
Edit it 'plot_wind.mv' and visualise it using the play button. Try to set a different level at the top of the macro.
Tephigram plotting
Macro 'plot_tephi.mv' demonstrates how to extract and plot TEMP ODB data into a tephigram (it is a type of thermodynamic diagram to show atmospheric profiles). Edit the macro and visualise it. Try to change the station specified at the top of the macro code.
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