![](bg6.png)
tor data by storing the center of each cell, or storing
the geometries of the cells. In this scenario – with
proper indexing – not only subsetting could be faster,
but sparse matrices and multiresolution images could
also be stored with ease.
Similarly, developers can choose the best ratio
of memory consumption and rendering performance.
For example, if hardware-acceleration is used, the tri-
angulation of the whole layer can be stored, gradu-
ally increasing performance on the expense of mem-
ory consumption. However, additional memory re-
quirement can also be fine-tuned. For example, one
must store at least two floating point values per ver-
tex, which can be complemented with four byte val-
ues (RGBA colors) for maximum performance. On
the other hand, colors can be defined dynamically, on
the fly, in order to decrease memory consumption. In
cases when memory footprint should be kept at min-
imum, the tessellation can be triangulated on every
drawn frame. Alternatively, if both the rendering en-
gine and the application requirements permit it, the
coverage can be rendered on a texture, and reused un-
til the map scale changes.
4 CONCLUSIONS
The raster model is still a dominant, widely used
model in GIS, although it has numerous limitations.
Its fundamental advantage comes from its matrix na-
ture, as it has well-optimized, fast algorithms, which
can effectively be parallelized. On the other hand, its
disadvantages – mostly coming from its representa-
tion model – are also severe. Its rectangular grid is
based on euclidean geometry, therefore it can only
map spherical surfaces and volumes with distortions.
It is also vulnerable to transformations, and hard to
reproject.
On the other hand, the vector data model does not
have these limitations; vectors can be arbitrarily and
accurately reprojected or interpolated. They require
more computing power for those operations, however,
modern personal computers have the computing ca-
pacity required for a vector-based coverage model.
Furthermore, vectors have the unique ability of stor-
ing many attributes linked to a single entity, and well-
optimized spatial Database Management Systems ca-
pable of analyzing them.
The coverage model we are proposing in this pa-
per makes possible to use non-rectangular tessella-
tions similarly to traditional rasters. Its practical im-
plementation seems straightforward, as it does not
collide with database standards, and can be integrated
into raster data exchange formats with minimal mod-
ifications. On the software side, as the simple form of
the proposed model would only require affine trans-
formations and a vector rendering engine, thus adding
it to modern GIS software would have no conceptual,
nor practical limits.
ACKNOWLEDGEMENTS
This study was supported by the
´
UNKP-17-3-I New
National Excellence Program of the Ministry of Hu-
man Capacities, Hungary. The authors would like
to thank the five anonymous reviewers for their con-
structive comments on the first version of this article.
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