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Save the changes and visualise the icon. Drop the GRIB data icon into the Display Window to see it on the new map. It is also possible to visualise the GRIB icon and then drop the Geographic View icon into the plot to achieve the same effect. Have a look at some of the other projections on offer, then go back to polar stereographic.
Now we want to set the area used in the view. Although we can interactively zoom into smaller areas in the Display Window, we now want to store a particular area so that we can use exactly the same one again and again. Set the Map Area Definition to Corners and click on the Geography Tool button next to the Area parameter (shown in the picture above).
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Future versions of Metview will incorporate more advanced plot-editing facilities available directly from the Layers tab. You can close the Display Window again.
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Modifying the Contouring
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Metview provides many ways to style the contours when plotting data. These are controlled via the Contouring icon. Create a new instance of this icon and rename it to shade. Edit it, setting the following parameters:
Contour Shade | On |
Contour Shade Method | Area Fill |
Contour Shade Max Level Colour | Red |
Contour Shade Min Level Colour | Blue |
Contour Shade Colour Direction | Clockwise |
Apply the changes, visualise the data icon again (t1000.grb) and drag the shade icon into the Display Window.
Our palette is automatically generated from a colour wheel. Try setting Contour Shade Colour Direction to Anti Clockwise to see the difference in the generated palette.
Creating a Legend
Create a legend by changing the first parameter in the Contour editor and dragging the icon into the Display Window again:
Legend | On |
Fixing the Contour Levels
Now zoom in and out of different areas. What happens to the palette - does it stay constant? The default behaviour is to create contours at 10 levels within the range of data actually plotted. As the area changes, so does the range of values being plotted.
Let's create a palette which will not be altered when we change the area. Copy the shade icon (either right-click + duplicate, or drag with the middle mouse button), and rename the copy 'fixed_t' by clicking on its title. Edit the icon and make the following changes:
Contour Level Selection Type | Level List |
Contour Level List | -5/0/5/10/15/20/25 |
Contour Shade Colour Direction | Clockwise |
Now when you apply this icon you will see that the palette is fixed wherever you zoom. There will probably be parts of the plot which are not filled; this is because our range of contour levels does not cover the whole range of values in the data. Change the list of contour levels so that the whole plot will be covered - you only need to add one number to each end of the level list to do this (or else change the current numbers at the ends of the list).