AN EFFICIENT MODULARIZED DATABASE STRUCTURE FOR A HIGH-RESOLUTION COLUMN-GRIDDED MARS GLOBAL TERRAIN DATABASE

Abstract

This paper discusses a modularized design for a Mars Global Terrain Database. The design provides for elevation data with respect to a triaxial ellipsoidal reference datum developed for Mars by USGS. Terrain data is recorded for 1-second of arc almost square grid elements over the surface of Mars. A 2000-Gigabyte column-gridded relation called Terrain contains the surface terrain data. Data for Terrain is expected in 1999-2000 from the Mars Global Surveyor satellite currently in initial polar orbit around Mars. Each tuple of Terrain contains data for a N-S column-grid of 900 1-second grid elements. There is thus a set of tuples per 1-degree rectangle, with the number of tuples per set decreasing with the cosine of latitude. Surface resolution is 16.5 meters or better. The design constrains tuple sizes in Terrain to permit efficient blocking and manipulation of the records of the underlying storage file. Terrain contains a virtual-attribute function for geodetic computations relating to the triaxial ellipsoidal reference datum. The database also relates Mars feature-type relations to Terrain. Terrain's gridded structure is transparent to users writing SQL expressions to retrieve Terrain data on the basis of specific features. Many different distinct feature-type relations can be included. At least two of these participate in recursive relationships. The design also allows attachment of additional feature-type relations in a modular manner, correctly related to Terrain, without affecting the contents of Terrain. The design is intended to enable efficient exploration of the planet at all levels of scale.