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bounded frame rate, (Funkhouser and S
´
equin, 1993)
have presented a predictive technique that uses an es-
timate of the execution time for the correct choice of
the LoD to use. The core of this work is a multiple
choice knapsack problem that maximizes the visual
quality for a given maximum execution time. The
greedy solution of Funkhouser and S
´
equin however
only guarantees to be half as good as the optimal so-
lution. Therefore, (Gobbetti and Bouvier, 2000) have
proposed to use convex optimisation (interior point al-
gorithm) with a guaranteed specified accuracy.
1.2 Image-based Rendering
As a solution for faster rendering of large geomet-
rical models, Image-Based Rendering (IBR) has re-
ceived many followers over the last years. The render
times of image-based models are fairly constant and
rely on the resolution of the reference images instead
of polygon count. This means that for high polygon
count models, image-based rendering can be a much
faster render solution without introducing too much
visual degradation. For closeup viewing of detailed
models however, conventional polygon rendering is
often still preferred. McMillan first proposed the fun-
damental 3D warping equation together with an oc-
clusion compatible warping order to efficiently render
new views based on a series of reference depth im-
ages (McMillan and Bishop, 1995). Extensions to this
have been presented in (Shade et al., 1998), (Oliveira
and Bishop, 1999) and (Chang et al., 1999) whereby
separate models are represented by a cluster of refer-
ence images.
More recently, (Oliveira et al., 2000) shows that
a factorisation of the 3D warping equation, called
relief-texture mapping (RTM), enables the use of fast
graphics hardware for part of the calculation to speed
up the warping. Warping is done in two steps: a pre-
warp followed by a simple texture mapping. This
delivers a significant speedup because the pre-warp
is implemented using a fast two-pass reconstruction
algorithm and the texture mapping can be done on
fast graphics hardware. Layered Relief Textures pre-
sented in (Parilov and Stuerzlinger, 2002) combine
the idea of storing multiple samples per pixel with fast
hardware assisted warping of RTM. Finally, (Fujita
and Kanai, 2002) incorporate dynamic shading into
the RTM approach by using per-pixel shading hard-
ware.
1.3 Qos for Mixed Systems
Conventional texture mapping can be seen as a very
simple form of image-based rendering that does not
take depth information into account. Based on this,
(Maciel and Shirley, 1995) focus on maintaining a
high framerate by replacing clusters of objects with
simple texture mapped primitives. Similarly, (Shade
et al., 1996) use a BSP tree scene representation for
which they cache images of nodes that were rendered
in previous frames. Taking frame-to-frame coherence
into account they reused these cached images for ren-
dering subsequent frames, thereby gaining a signifi-
cant rendering speedup.
Later on, making use of depth image representa-
tions, (Rafferty et al., 1998) extend a portal culling
renderer in which they determine the view through a
portal by warping a precalculated Layered Depth Im-
age (LDI) that captures the view through that portal.
This approach is generalized for massive model ren-
dering in (Aliaga and Lastra, 1999). A grid of view-
points is constructed for which the far geometry is de-
termined after which LDIs are created that represent
this far geometry. The renderer can then first render
far geometry from LDIs followed by polygon based
rendering of the near geometry. The MMR system
(Aliaga et al., 1999) replaces the LDIs in the previous
approach by Textured Depth Meshes (TDMs) to make
optimal use of current graphics hardware.
Two fundamental drawbacks of the former hy-
brid techniques are the often very long preprocess-
ing times and huge storage requirements. Therefore,
a system that creates image-based representations on
demand without the need for additional storage was
presented in (Hidalgo and Hubbold, 2002). They em-
ploy a dual renderer setup in which the hybrid ren-
derer (HR) can request reference depth images rep-
resenting the current far geometry from a reference
image generator (RIG) that runs in parallel. While
the RIG is working on the requested data, the HR can
use warping on the previous reference depth image to
render its frames. Prediction is used to request opti-
mal reference images.
A specific optimization algorithm for a terrain fly-
over application was proposed in (Zach et al., 2002).
Interesting in this approach is that they not only use
discrete and continuous Level Of Detail for polygonal
rendering but also point-based rendering for the trees
on the terrain.
A major drawback of these approaches is that they
are not well suited for handling dynamic scenes for
which the contents is not known beforehand. This
is the case for instance for the increasingly popu-
lar MMORPGs. We have therefore selected to use
the hybrid rendering technique presented in (Jehaes
et al., 2004), which was extended to mobile devices
in (Jehaes et al., 2005). This technique uses a com-
bination of progressive geometry and relief texture
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