High Quality Content by WIKIPEDIA articles! The Palomar Testbed Interferometer (PTI) was a near-IR, long-baseline stellar interferometer located at Palomar Observatory in north San Diego County. It was built by Caltech/JPL and was intended to serve as a testbed for developing interferometric techniques to be used at the Keck Interferometer. It began operations in 1995 and achieved routine operations in 1998, producing more than 50 refereed papers in a variety of scientific journals covering topics from high precision astrometry to stellar masses, stellar diameters and shapes. PTI concluded operations in 2009.