
allow higher artistic control following the inverse procedural
modeling concept used by Talton et al. [6]. Vanegas et al. [7]
presented a model for combining behavioral modeling (e.g.
population density distribution, job distribution, high access,
land usage) and geometric modeling (e.g. road width and
number of lanes, building area, number of floors), allowing
the changes made in a certain parameter to impact on every
element of the city layout. Vanegas et al. [8] presented a
model where, given an initial city model, adjustments using an
MCMC method are made to approximate a set of parameters
(e.g. parcel average area, road curvature, building height)
defined by the user. The model presented by Aliaga et al.
[9] allows the user to draw the distribution on land usage
(e.g. urban regions, agricultural regions, bodies of water) on
the base terrain to create weather simulations. Roads and
buildings for urban regions are adjusted using a Metropolis-
Hastings algorithm [10], [11], an MCMC method, to explore
the search space and find similar results to the user-specified
weather. Specifications can include cloud coverage per region,
humidity, rain distribution, and city temperature. Mustafa et
al. [12] presented a model for the generation of urban layouts
that passively reduce water depth during flood scenarios. This
work combines a procedural generation model with a hydraulic
model to evaluate water flow characteristics for the created
region. A neural network is used to identify relationships
between the urban layout and the flow of water during floods,
which are used as input to an MCMC model, adjusting
the environment. The evaluation takes into consideration the
desired building coverage and average water depth, etc.
Populations and crowds can be simulated with varying
levels-of-detail, with a trade-off between accuracy and compu-
tational performance. While a microscopic crowd simulation
offers individual characteristics and decision making for each
agent, it can be prohibitively computationally demanding when
simulating an environment such as an entire city. Macroscopic
crowd simulation models group up agents to reduce the
granularity of the simulation and simulate larger crowds. One
of such models is BioClouds [13], a crowd simulation model
which offers collision avoidance based on space discretization
and competition. BioClouds models crowds as clouds, i.e.,
groups of similar minded agents, which have a desire for a
certain density, speed and goal. Clouds compete for space
amongst each other, and occupy the environment in a manner
that tries to keep their desired densities respected.
If on one hand, BioClouds simulate macroscopically groups,
sometimes the microscopic simulation of people is needed.
The crisis caused by the new Corona Virus and the global
spread of COVID-19 cases turned the attention of scientific
community to the spreading disease problem. Some research
groups are focusing on SIR [14] (further formulated in Sec-
tion III-B) and SEIR [15] mathematical models to attempt
to predict when the flatten of contagion curves will occur. It
is of major importance to predict those curves, given every
scenario [16]. Authorities must be able to decide when to
open schools, stores and shopping centers with the objective
to protect children education and jobs, minimizing the risk of
endangering public health.
In this paper we use the model proposed by Antonitsch [13],
where we do not simulate individuals, but groups, in a
macroscopic level. Therefore, we also propose to include in
LODUS a microscopic simulation using BioCrowds in order
to have individuals. Our goal is to customize BioCrowds
to program agents to attempt to keep recommended social
distance. Then, we extract information about social distancing
simulation to estimate contagion rates for micro-environments,
then we extrapolate those data for macroscopic simulation.
III. LODUS: LEVEL-OF-DETAIL ON URBAN SIMULATION
The ability to predict and analyze urban dynamics scenarios
is a key and distinctive support for the work of city managers
and urban planners. This paper presents LODUS, a framework
able to simulate virtual urban environments with various levels
of details. LODUS main goals is to provide information
in order to collaborate on the challenge of city planning
and management. Figure 1 illustrates the architecture of the
proposed framework.
Fig. 1. LODUS Architecture.
LODUS is a multi-level model able to be configured in two
ways: i) reproducing scenarios of real world or ii) simulating
urban dynamics before the introduction of changes in real
life. In both cases, it is important that environment and
population could be coherently simulated. The next sections
describe in details every module which compose our multi-
level framework.
A. Environment
This module allows the representation of an environment
with different levels of abstractions. At each level, a more
detailed representation of the environment may be defined. As
a deeper level is included, more detailed information can be
computed. Such details store different data, such as population
distribution, road system, buildings’ geometry or even internal
buildings setups. Figure 2 presents the steps performed on the
environment construction.