AN EFFICIENT MODULARIZED DATABASE STRUCTURE FOR A HIGH-RESOLUTION COLUMN-GRIDDED MARS GLOBAL TERRAIN DATABASE
Date
1998-11-01
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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.
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Computer Science