https://doi.org/10.31449/inf.v44i1.3114 Informatica 44 (2020) 109–110 109
Interactive Synthesis and Visualisation of Vast Areas with Geometrically
Diverse Trees
Štefan Kohek
Faculty of Electrical Engineering and Computer Science, University of Maribor, Slovenia
E-mail: stefan.kohek@um.si
Thesis summary
Keywords: generation of trees, particle flow simulation, GPU, volumetric rendering
Received: April 9, 2020
This paper summarises a Doctoral Thesis which proposes a new approach for large-scale forest visuali-
sation with geometrically diverse trees. The main contribution of the proposed method is an interactive
visualisation of numerous trees without generating geometric data in advance, which is achieved by a new
method for on-the-fly tree skeleton synthesis with a specific level of detail, and by a new procedural volu-
metric tree crown visualisation which avoids geometry formation altogether. The proposed method enables
visualisation of forests with millions of trees, thus allowing rendering more trees than geometry-based vi-
sualisation methods.
Povzetek: Prispevek povzema doktorsko disertacijo, ki predlaga nov pristop za upodabljanje obsežnejših
gozdov z geometrijsko raznolikimi drevesi. Glavni prispevek predlagane metode je interaktivno upodabl-
janje veˇ cjega števila dreves brez potrebe po vnaprej pripravljenih geometrijskih podatkih, kar dosežemo z
novo metodo za sprotno tvorbo okostij dreves v doloˇ cenem nivoju podrobnosti in z novo metodo za vol-
umetriˇ cno upodabljanje krošenj dreves, ki se v celoti izogne tvorbi geometrijskih podatkov. Predlagana
metoda omogoˇ ca upodabljanje gozdov z milijoni dreves in tako omogoˇ ca upodabljanje veˇ cjega števila
dreves kot metode na podlagi vnaprej pripravljenih geometrijskih podatkov.
1 Introduction
Trees are natural objects which consist of numerous leaves
and branches. Various applications require convincing vi-
sualisation of vast areas with trees. In contrast to artificial
objects, which consist mainly of flat surfaces, trees are ge-
ometrically more complex and require significant amounts
of memory for geometric representation. Therefore, large-
scale visualisation of geometrically diverse trees is chal-
lenging, due to memory constraints. Numerous techniques
for forest rendering were developed in the past [1], which
only partially address these issues through various tech-
niques (e.g., instancing, pre-processing, or parallelisation).
This paper summarises a PhD thesis [2], which proposes
a comprehensive pipeline for large-scale synthesis and vi-
sualisation of geometrically diverse trees. The main find-
ings are published in the corresponding paper [3]. The
following sections summarise the proposed approach, the
main results and findings.
2 Overview of the proposed method
The main aim of the proposed approach is interactive vi-
sualisation of numerous geometrically diverse trees while
navigating through the forest. In order to achieve convinc-
ing visualisation of nearby trees, the nearest trees need to
be visualised at the highest level of detail. In contrast, more
distant trees can be visualised at lower levels of detail with
lower memory requirements. However, in the case of mil-
lions of trees, geometric data of at least the most distant
trees need to be omitted altogether due to memory limita-
tions.
The trees in the proposed approach are generated pro-
cedurally by a new tree synthesis algorithm, based on a
particle flow simulation, which generates tree skeletons of
branches and leaves. The target tree structure is defined by
a tree crown envelope and a few parameters, which define
the branching pattern. The generated tree skeletons are vi-
sualised by generating actual geometric data directly on a
Graphics Processing Unit (GPU).
In order to generate more distant trees without post-
processing directly at lower levels of detail, multiple sim-
plification schemes are introduced and integrated directly
into the tree skeleton construction. However, tree synthe-
sis needs to be fast, in order to achieve low latency of on-
the-fly tree synthesis while navigating through the forest.
Therefore, a new parallel tree synthesis algorithm for di-
rect execution on the GPU is proposed, which is designed
specifically for parallel tree synthesis of numerous trees.
To avoid geometry formation of the most distant trees
completely, the thesis proposes a new procedural volumet-
ric visualisation algorithm of tree crowns within the graph-

110 Informatica 44 (2020) 109–110 Š. Kohek
ics pipeline. Based on the defined tree crown envelopes, the
volumetric visualisation method achieves identical appear-
ance in comparison to the geometry-based visualisation. In
this way, visual continuity is preserved when switching be-
tween the geometry-based and volumetric visualisation.
Finally, a new quad tree based framework is proposed,
which integrates tree synthesis and visualisation algorithms
to enable interactive visualisation and on-the-fly synthesis
of the nearest trees while navigating through the forest.
3 Results
The proposed method was verified in terms of the tree syn-
thesis duration, forest rendering rates, interactivity when
navigating through forests, and similarity preservation of
trees generated at lower levels of detail to the trees gener-
ated with the highest level of detail. Forests consisting of
400,000 branch segments were generated in less than 25
ms on the GPU Nvidia GTX 1060 with 4 TFLOPS of pro-
cessing power, which enables generating larger numbers of
trees between individual frames and preserving interactive
rendering rates. Generating the trees with the lower levels
of detail accelerated the synthesis even further, and enabled
higher rendering rates. Additionally, the proposed simpli-
fication schemes generally achieved a gradual transition of
similarity with the lower amount of memory. Hausdorff
distance and precision and recall metrics, which were used
for calculating similarity, agreed with these findings.
Performance of the geometry-based rendering was re-
lated closely to the amount of branch segments and leaves.
In contrast, procedural volumetric rendering outperformed
geometric rendering at a higher number of leaves or at a
lower rendering resolution, which coincides with the vi-
sualisation of more distant trees. Overall, the proposed
framework achieved stable rendering rates of more than
12 frames per second when displaying forests consisting
of one million of trees.
4 Conclusion
The PhD thesis [2] has proposed a new comprehensive for-
est visualisation method, which enables detailed visualisa-
tion of close up trees and large-scale visualisation of distant
trees without requiring the existing tree geometry. Proce-
dural volumetric rendering is useful, especially for visuali-
sation of distant trees, while a combination of tree skeleton
synthesis and geometric rendering is used for the nearest
trees.
References
[1] Smelik, R. M., Tutenel, T., Bidarra, R., and Benes, B.
(2014). A Survey on Procedural Modelling for Virtual
Worlds. Computer Graphics Forum, 33(6): 31–50.
https://doi.org/10.1111/cgf.12276
[2] Kohek, Š. (2019). Interaktivna tvorba in prikaz ob-
sežnih podroˇ cij geometrijsko raznolikih dreves : dok-
torska disertacija. PhD thesis, Univerza v Mariboru,
Fakulteta za elektrotehniko, raˇ cunalništvo in infor-
matiko.
[3] Kohek, Š., and Strnad, D. (2018). Interactive large-
scale procedural forest construction and visualization
based on particle flow simulation. Computer Graph-
ics Forum, 37(1): 389–402.
https://doi.org/10.1111/cgf.13304