Digital elevation model

SaVoir will handle intersection calculations and swath footprints taking into account the Earth digital elevation model (DEM). Alternatively it can revert to the Earth WGS84 Ellipsoid instead.

The DEM is modelled with a 21600 x 10200 pixel height map, yielding a ground resolution of circa 2 km per pixel. Loading other height maps with different resolution is possible via the Edit / Properties... dialog. Note, however, that the height map is loaded in memory for fast access and it can occupy significant amount of RAM, therefore it advisable to avoid pushing the height map resolution too high.

The effect of the DEM is a side-shift of the swath footprint and some distortion of the swath edges. The effect is more accentuated at high elevations and with highly slanted look angles.

In the example below, a small area of interest over the Andes, close to Santiago de Chile, is covered with Cosmo-Skymed 1, HIMAGE mode. The area is located at circa 5000 meter altitude. The images below show the swath footprint obtained by SaVoir with both Ellipsoid and DEM, showing the expected side-shift due to altitude.

Ellipsoid	DEM over ellipsoid

The footprint with DEM can be also rendered at high resolution. A new feature allows to build the swath in high or low resolution, by right click menu on the swath footprint. It is also possible to build all visible swaths in high resolution with the Tools / Build high resolution menu.

When built at high resolution, the swath footprint will be calculated with many more points and will display the expected distortion at the edges.

The high resolution effect is demonstrated below, comparing with the Ellipsoid and DEM Low resolution footprints below.

Ellipsoid	DEM over ellipsoid