The European Space Agency's Envisat-1 is an advanced polar orbiting Earth observation satellite that provides measurements of the atmosphere, ocean, land, and ice. It is expected to be in orbit for at least five years.

Fig 1: The Envisat

ESOV is a software package that provides the user with the means to visualize where each instrument on the satellite will be effective on its orbit of the Earth. It currently knows about the ERS-1, ERS-2 and ENVISAT satellites. Its main purpose is to assist in understanding where and when a satellite's measurements are to be made.

The European Space Agency, as a current user of our products, approached us to deploy our expertise in cross platform development to the huge amount of legacy code that constituted the ESOV product.

In order to create a single source base it was necessary to restructure large portions of the code for efficiency and update it for C++. We did this in three phases.

Firstly, the original interface was created with X-Designer our flagship product. That allowed us to move the user interface code from a Motif base to Windows MFC code with relative ease. Only a few changes were necessary to ensure the interface was consistent on both platforms.

The second challenge in enabling a single source code base regardless of platform was to remove all of the platform specific references to libraries that are not common. To do this we made use of X-Designer's Motif XP libraries. These are mapping classes that reflect the Microsoft Foundation Classes for each of the graphical components used in Motif. As the libraries are fully extensible we were able to expand upon the existing library to cover the more advanced manipulation of the interface components.

The third phase was the lower level code, the X Drawing routines. For this it was necessary to create a completely new library to handle all of the drawing code for both platforms. Using the Java API as a loose model for the graphics we devised a set of drawing routines that allowed us to make use of the same graphics calls to draw the Earth in its various projections and all of the satellite and plotting details. This generic library allows all of the graphics calls to work regardless of platform.

The ability to run the ESOV product on Windows now makes the product more accessible to a greater number of users and far more flexible. We have since undertaken a second piece of work to expand the ESOV product even further.

After the initial 'port' to windows we were recontracted to begin adding new features to the existing base product and also to enhance the existing mechanisms within the application. New features included PDF generation, Visualisation projection for the recently launched Artemis satellite, new outputs for satellite and instrument visibility on the Earth's surface as well as significant interface enhancements.