Insofar, most research
in SOLAP has been done with the needs of the former group in mind. We can say
that today??™s research community is succeeding in bringing spatial data into the
OLAP arena. However, major challenges remain for the next several years in order
to satisfy the needs of more advanced users. We still need to bring OLAP capabilities
into the geomatics engineering arena.
Particularities.of.Spatial.Data
Computer displays are flat; however the Earth is not. Furthermore, it is not a simple
sphere nor a simple ellipsoid flattened at the poles. Earth??™s true shape looks more
like a nice potato and it is scientifically defined as the geoid. The geoid is an equipotential
surface that corresponds to the mean sea level. This physical model is the
mathematical figure of the Earth as defined by its irregular gravity field. It is the
model used by national mapping agencies to produce topographic maps upon which
most thematic maps are based. It is more irregular than the ellipsoid of revolution
because of the irregularities of the Earth surface (19,000 meters from the top of
Mount Everest to the bottom of Mariana Trench) and because of the different densities
associated with different types of minerals. The difference between the ellipsoid
and the geoid can be up to 100 meters but we project our measurements on the ellipsoid
to simplify the mathematics and to remain more stable over time (the geoid
changes over time).
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