Open Modular Interactive Mapping Technology
for Visualization of Geophysical Data on the Internet


4. Applications

Contour lines of geomagnetic field

Here we will give two examples of interactive visualization of time varying vector fields on a regular grid in different projections using the MapApplet. We use spidrjmap add-in module in the first example.

In Fig. 14 the specified task is to show locations of geomagnetic observatories on the map together with the isolines of the Earth�s main magnetic field. The vector-valued magnetic field has 3 components and slowly changes in time. Every 5 years the main field parameters are approximated by using the IGRF-model.

Our application server inserts into the web page the list (JavaScript array) of geomagnetic observatories with indication of their code, name and coordinates. After the MapApplet confirmation that it is loaded and initialized (see above), a special JavaScript function sends the list of the station names and coordinates to the MapApplet, and they are plotted on the map. When user selects a station on the map, it is also selected in the multiple selection list in the HTML form on the page. When station is selected in the form, it is shown as selected on the map by the MapApplet with different color.

It is then possible to overlay contour lines of the magnetic field on the map. The user selects the year of the IGRF model and the parameter of the magnetic field in the HTML form on the web page. JavaScript sends the user choice to the MapApplet. The MapApplet downloads a data file with spherical harmonics coefficients from the application server, calculates the field on the regular grid, and draws contour lines on the map.

IGRF model:    

Figure 14. Locations of geomagnetic observatories on the map together with isolines of the Earth�s main magnetic field
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