Volume 37 (2018), number 1 pp. 389–402
Interactive Large-Scale Procedural Forest Construction and
Visualization Based on Particle Flow Simulation
and Damjan Strnad
Faculty of Electrical Engineering and Computer Science, University of Maribor, Slovenia
Interactive visualization of large forest scenes is challenging due to the large amount of geometric detail that needs to be
generated and stored, particularly in scenarios with a moving observer such as forest walkthroughs or overﬂights. Here, we
present a new method for large-scale procedural forest generation and visualization at interactive rates. We propose a hybrid
approach by combining geometry-based and volumetric modelling techniques with gradually transitioning level of detail (LOD).
Nearer trees are constructed using an extended particle ﬂow algorithm, in which particle trails outline the tree ramiﬁcation in an
inverse direction, i.e. from the leaves towards the roots. Reduced geometric representation of a tree is obtained by subsampling
the trails. For distant trees, a new volumetric rendering technique in pixel-space is introduced, which avoids geometry formation
altogether and enables visualization of vast forest areas with millions of unique trees. We demonstrate that a GPU-based
implementation of the proposed method provides interactive frame rates in forest overﬂight scenarios, where new trees are
constructed and their LOD adjusted on the ﬂy.
Keywords: novel applications of the GPU, level-of-detail algorithms, particle systems
ACM CCS: I.3.5 [Computer Graphics]: Computational Geometry and Object Modelling; I.6.8 [Simulation and Modelling]:
Types of Simulation—Parallel, Visual
Computer games, ecosystem simulations and virtual reality applica-
tions regularly require visualization of vast forest areas. Interactive
visualization of such scenes remains challenging even for modern
hardware. Because each tree requires a large amount of geometry
for convincing visualization, modelling whole forests using geo-
metric representation rapidly exhausts normally available memory.
Various level-of-detail (LOD) techniques have been proposed for
the rendering of extensive forest regions, but they assume intensive
model pre-processing and storage at all levels of geometric detail.
On the other hand, image-based techniques (e.g. impostors and bill-
boards) enable visualization of huge forest areas but struggle with
a realistic display of unique looking trees.
Procedural on-the-ﬂy geometry generation is not widely used
for tree models due to its high processing and space requirements.
The interaction of trees with their environment and rendering of
models at gracefully transitioning LODs determined at run-time
additionally aggravate the efﬁcient application of forest generation
methods. Existing approaches only partially address these issues
through pre-processing or parallelization, which prevents instant and
dynamically adaptive visualization of vast forest-populated areas.
In this work, we present a new approach for interactive large-
scale forest construction and visualization. Trees are modelled using
an enhanced particle ﬂow algorithm, which enables intuitive tree
crown shaping and extends the modelling versatility of the original
approach [RCSL03]. The method is implemented with OpenCL
[Khr12] and executed entirely on a graphics processing unit (GPU),
allowing massive parallelization of individual model construction,
as well as concurrent generation of a large number of unique trees.
It also eliminates lengthy transfers of tree geometry from CPU to
GPU, thereby allowing instant visualization of rendered scenes.
We introduce various LOD schemes with the particle-based
method for the modelling of trees that do not require full detail.
Geometric LOD techniques rely on the underlying particle ﬂow
2017 The Authors
Computer Graphics Forum
2017 The Eurographics Association and
John Wiley & Sons Ltd. Published by John Wiley & Sons Ltd.