Two fixed black-and-white cameras on Cartosat-1, one tilted forward and one tilted back, which photograph the same ground about 50 seconds apart to make 3D maps.
Each camera takes black-and-white pictures at 2.5 m resolution over a 30 km strip. ISRO describes 2.5 m as enough to make out a small car.
The forward camera (PAN-F) is fixed at a tilt of 26° ahead. The aft camera (PAN-A) is tilted 5° back. As the satellite flies, the forward camera sees a patch of ground first, and the aft camera sees it again about 50 seconds later from a different angle.
Two pictures from different angles work like our two eyes. Software measures the small shifts between them to work out the height of the ground.
Cartosat-1, launched by PSLV-C6 in May 2005, was the first Indian satellite to take stereo pictures in orbit. Its stereo pairs were used to build digital elevation models and map-quality images for planning and GIS.