User's Guide


Contents

The Graphical User Interface
- The Basemap Panel
- The Geomagnetic Field Calculation Panel
The Map Window
How to Plot an Isomagnetic Map?
How to Select Your Own Contour Levels?


The Graphical User Interface

The IGRF-applet contains a graphical user interface (GUI) that enables the user to select the desired parameters for map plotting and geomagnetic field calculation. The GUI also enables the user to start the map plotting process that produces a map window containing an isomagnetic map, a map header and a menubar (see The Map Window). Figure 1 shows what the GUI looks like.


Figure 1: The graphical user interface.

The GUI is divided into two panels:

The Basemap Panel

The South West Corner and the North East Corner subpanels (see figure 1) contain Latitude and Longitude text fields where you enter the desired south west (SW) and north east (NE) map corners (see figure 2). Negative latitude values indicate southern (S) and positive latitude values indicate northern (N) latitudes. Negative longitude values indicate western (W) and positive longitude values indicate eastern (E) longitudes.


Figure 2: The south west and north east map corners.

The map corner latitudes must obey the following rules

latNE - latSW >= 10°,
-90° <= latSW < latNE and
latSW < latNE <= 90°

and the map corner longitudes must obey the following rules

lonNE - lonSW >= 10°,
-180° <= lonSW < lonNE and
lonSW < lonNE <= 180°.

Select the desired map projection from the Map projection pull down list (see figure 1). There are three items on the list: the Van Der Grinten, the Eckert and the Miller items.

The Van Der Grinten and the Eckert projections are suitable for World maps and the Miller projection (which is equivalent to the Mercator projection) is suitable for smaller sized maps. The following are examples of maps plotted using the above projections:

Select the desired shoreline database from the Shoreline database pull down list (see figure 1). There are two items on the list: the Low resolution and the High resolution items.

The low resolution shoreline database is for World maps and the high resolution shoreline database is for smaller sized maps. The following are examples of maps plotted using the two shoreline databases:

Select the desired hierarchy level from the Hierarchy level pull down list (see figure 1). There are two items on the list: the Land and the Lakes items.

The hierarchy level defines up to which hierarchy level shorelines are plotted. The following are examples of maps plotted using the two hierarchy levels:

The Geomagnetic Field Calculation Panel

The Spherical Harmonic Expansion subpanel (see figure 1) contains the n text field where you enter the harmonic degrees (the set of multipoles) used in calculating the multipole expansions of the X-, Y- and Z-components. Separate the harmonic degrees with commas. The harmonic degrees must be between 1 and 10.

The Spherical Harmonic Expansion subpanel (see figure 1) also contains the Expansion pull down list that you can use to quick select the harmonic degrees (the n text field will be automatically filled). There are three items on the list: the Total field, the Dipole field and the Non-dipole field items.

Select the desired magnetic element from the Magnetic element pull down list (see figure 1). There are seven items on the list: the Total Intensity, the Horizontal Intensity, the North Component, the East Component, the Vertical Component, the Declination and the Inclination items.

Turn on the Calculate secular variation check box (see figure 1) to calculate the secular variation of the selected magnetic element.

Enter the desired date into the Date text field. The date must be between 1900 and 2005.

Enter the desired altitude into the Altitude text field. The altitude must be between -2500 and 25000 kilometers.

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The Map Window

When the map plotting process is finished a map window will be displayed. It contains an isomagnetic map, a map header and a menu bar. Figure 3 shows what the map window looks like.


Figure 3: The map window.

The menu bar contains two menus, the Frame and the Levels menus (see figure 3). The Frame menu contains only one item, the Close item. By selecting the Close item you can close the map window. The Levels menu also contains only one item, the Edit item. By selecting the Edit item you can select your own contour levels (see How to Select Your Own Contour Levels?).

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How to Plot an Isomagnetic Map?

1. Select the desired parameters

To select the desired parameters use the graphical user interface (see The Graphical User Interface).

2. Press the Plot button

Press the Plot button (see figure 1) to start the map plotting process.

3. Wait until the map plotting process is finished

The map plotting process consists of three phases. In the first phase the basemap is plotted using the selected shoreline database and hierarchy level. The progress indicator of figure 4a is displayed during the first phase. In the second phase the values of the selected magnetic element are calculated. The progress indicator of figure 4b is displayed during the second phase. In the third phase the isomagnetic lines are calculated and plotted. The progress indicator of figure 4c is displayed during the third phase.


Figure 4: The progress indicators displayed during the map plotting process.

The map plotting process can be aborted during any of these three phases by pressing the Abort button on the progress indicators (see figure 4).

When the map plotting process is finished a map window that contains the isomagnetic map will be displayed (see The Map Window).

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How to Select Your Own Contour Levels?

1. Select the Edit item from the Levels menu

Selecting the Edit item from the Levels menu (see The Map Window) will pop up a level editor (see figure 5).


Figure 5: The level editor.

2. Edit the contour levels

You can remove existing contour levels and enter new contour levels using the level editor (see figure 5). Enter only one contour level per line.

3. Press the OK button

To start the map plotting process press the OK button. To return without a change press the Cancel button. (See figure 5.)

4. Wait until the map plotting process is finished

The process of plotting an isomagnetic map using the edited contour levels has two phases. In the first phase the basemap is plotted. The progress indicator of figure 6a is displayed during the first phase. In the second phase the isomagnetic lines are calculated and plotted and. The progress indicator of figure 6b is displayed during the second phase.


Figure 6: The progress indicators displayed during the map plotting process.

The map plotting process can be aborted during any of these two phases by pressing the Abort button on the progress indicators (see figure 6).

When the map plotting process is finished a map window that contains an isomagnetic map plotted using the edited contour levels will be displayed (see The Map Window).

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Copyright © 2000 Kimmo Korhonen