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Giguere, et al., 1996). We look forward to seeing further
published descriptions about the methods, and whether they
are also applicable to the very large global datasets that
SOLIS is designed for.
3. DESIGN OF SOLIS
3.1 Overview
SOLIS is a hybrid language system that will make use of the
virtues of four languages. SYBASE SQL (Structured Query
Language) will be used for handling large tabular datasets,
such as those to be generated by the Mars 96 mission.
Prolog is being used for database program development and
for flexible rule-based queries. The procedural languages
Fortran and C are used to perform fast numerical
computations and raster image analysis. Currently an
interface between Prolog and Fortran/C has been achieved
and this is being used as a test-bed to decide upon the types
of commands needed to query the database. SQL has already
been used to conduct some experiments on querying tabular
data for eventual integration into the system (Cook et al.,
1994). Below we detail some important points concerning
the design of our database.
3.2 Data
Data held within SOLIS fall into seven classes: data about
images, cartographic vector and raster data, bibliographic
references to images and geographical features, digitized
graphs, tables of physical measurements, technical
spacecraft data, and small illustrative images/graphics.
I : 06.7068
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Figure 1: Top left: footprint hierarchy level 1, top right:
RT hierarchy level 2, bottom: footprint hierarchy
evel 3.
A one-off data-formatting program is required to generate the
Initial SOLIS database for each planet using, where possible,
the best available camera navigation parameters generated
from JPL's standard SPICE software and kernel files. Our
189
database design does not require the same precision as
SPICE, so can be both more compact, and performs
geographical searches faster.
In accordance with Mars 96 requirements, we adopt
planetographic longitudes and latitudes to describe spatial
positions on the planetary surface, and heights measured
with respect to a fitted triaxial ellipsoid reference datum.
Time tags applied to SOLIS data are either planet centred
ephemeris time (Julian Date) for observational data, or
geological age in the case of geological maps.
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Table 3: "image.tbl".
It is not possible to describe all of this in detail, therefore we
highlight some key aspects namely: how we store data about
images, the storage and access of digital global mosaic and
geological maps, and the "scientists notebook" facility to
be used during the Mars 96 mission, and how this can be
extended to include bibliographical references.
3.2.1 Data about Images: Our design must allow for all
existing planetary spacecraft camera systems, and also for
those likely to be onboard future missions. For each image
we need to store information concerning: image identifiers,
the image footprint outline, camera position(s), the location
of the planet in its orbit, illumination and viewing angle
conditions, and a description of the image. However it is also
necessary to keep storage requirements low, to be able to
handle upto several million image records, and to locate
certain records rapidly based primarily upon their geographic
location. To achieve the first two goals one main table,
"image.tbl" (table 3), has been used and its fields have been
selected carefully in terms of precision and number. This
results in a stripped down record size of only 108 bytes per
image. Compact storage is particularly important for an
existing dataset of just under 2 million records, concerning
images returned from the lunar Clementine spacecraft. Such a
large collection of image records occupies more than 200Mb
of disk space in this reduced file format alone.
The first four fields in "image.tbl" are unique identifiers to
each image. Images are usually referred to by their name or
spacecraft clock count. The Julian Date identifier may also be
used for computing illumination conditions and planetary
ephemeris data to higher precision, if this is required. The
imager ID, points to another table (not given here) which
lists combined spacecraft, camera, filter information.
Another useful item of data is the location of the planetary
object around the Sun; this can yield information about
seasons.
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996