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7 CONCLUDING REMARKS
We have presented a novel technique for represent-
ing and manipulating large terrain datasets. Its main
advantage is the possibility to efficiently update the
system with new heterogeneous grids, a character-
istic that is not found in any existing method. The
system automatically detects and removes redundant
data. Furthermore, our technique produces a multi-
resolution C
k
surface instead of a discrete model. The
actual evaluation of the surface, which is the only
computationally intensive task, can be demanded to
the GPU, while keeping the communication between
CPU and GPU limited. Texture and normal map can
be easily integrated, since they can be associated to
every patch and interpolated, with the same method
used for the height values.
The space overhead required by the multi-
resolution model is approximately the same as the
space used for a mipmap pyramid, thus it is suitable
to be used even with huge terrains. A limitation of
this technique is the lack of a theoretical bound on the
maximum number of patches that may overlap at a
single point of terrain. This can probably be avoided
if we insert additional criteria to the patch invariant
we use for building the spatial index, and it will be
one of the main points of our future work. However,
in our experiments the number of overlapping patches
never exceeded six, and it was four on average.
We have presented results obtained with our CPU
implementation, which is already able to obtain in-
teractive rendering frame rates using a single core on
moderately large terrains. The algorithm for the con-
struction and update of the multi-resolution model, as
well as the query algorithms are efficient and capable
to manage huge datasets.
We are currently working on a GPU implemen-
tation and the most relevant aspects to achieve effi-
ciency are: incremental queries, providing a stream
of differences between patches defining terrain in the
previous and current frame, which can be directly
transferred to the GPU; efficient update of the list of
patches maintained in the GPU; and the strategy for
parallel evaluation and meshing of terrain.
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