Space Oblique Mercator

A modified cylindrical projection with the map surface defined by a satellite orbit. Basically conformal, especially in region of satellite scanning.

 

Scale

 

Continuously true to scale along ground track of satellite.

 

Distortion

 

Near-zero distortion along ground track of satellite.

 

Usage

 

Used for mapping images from Landsat series satellites. May be used for any satellite orbiting the Earth in a circular or elliptical orbit and at any inclination.

 

Origin

 

Developed in 1973 - 1979 by Alden P. Colvocoresses, John Parr Snyder and John L. Junkins. Colvocoresses was the first to realize that such a projection was needed and mathematically feasible, and in 1974 defined it geometrically. Snyder created the definitive formulas for the projection in 1977 - 1979, while less complete formulas were also created by Junkins in 1977. Snyder provided a complete derivation for orbits of any ellipticity in 1981.

 

Optional Forms

 

The Space Oblique Mercator for Landsat is a pre-computed form of the Space Oblique Mercator projection that allows specification of the projection by citing a Landsat Orbit Number and Orbit Path Number.

 

Historical Note

 

J.P. Snyder is revered throughout professional cartography as one of the giants of computational cartography. He arrived late in life to his career with USGS after a previous career as a chemical engineer. The Space Oblique Mercator projection formulae created by Snyder launched his second career in cartography.

 

USGS had been unable to develop projection formulae that implemented Colvocoresses's geometric definition and made an open appeal for help at the 1976 geodetic conference at Ohio State University. Snyder attended the conference while on vacation (he had a hobby interest in cartography and would schedule his vacations to allow him to attend cartographic conferences) and heard the appeal. He developed the required formulae on a pocket calculator and donated them to USGS. In 1978 he joined the professional staff of USGS and began his second career at the age of 52 as a computational cartographer.