Glossary for Geospatial Science

video field:  The image you see on a standard TV screen is composed of a set of about 480 horizontal lines.  The lines are projected in two passes of the signal beam.  Each pass only projects every other line of the image: the odd lines in one pass, and the even lines in the next pass.  One scan takes 1/60 of a second, so the whole picture (the frame) is refreshed every 1/30th of a second.

A field contains every other line of the complete video image.  The primary field contains the odd lines; the secondary field contains the even lines.