AN EFFICIENT MODULARIZED DATABASE STRUCTURE FOR A HIGH-RESOLUTION COLUMN-GRIDDED MARS GLOBAL TERRAIN DATABASE
Date
1997-12-01
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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 grid elements over the surface of Mars. A 400 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 a uniform 16.5
meters everywhere with a 1-second grid. 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 are 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.
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Computer Science