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automatic什么意思三维建筑模型论文中英文资料对照外文翻译文献

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2021-01-21 20:32
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2021年1月21日发(作者:ove)

三维建筑模型

中英文资料










Constructing Rules and Scheduling Technology for 3D
Building Models

Zhengwei SUI, Lun WU, Jingnong WENG, Xing LIN, Xiaolu JI



Abstract

3D models have become important form of geographic data beyond conventional
2D
geospatial
data.
Buildings
are
important
marks
for
human
to
identify
their
environments, because they are close with human life, particularly in the urban areas.
Geographic
information
can
be
expressed
in
a
more
intuitive
and
effective
manner
with architectural models being modeled and visualized in a virtual 3D environment.
Architectural
model
data
features
with
huge
data
volume,
high
complexity,
non-uniform
rules
and
so
on.
Hence,
the
cost
of
constructing
large-scale
scenes
is
high. Meanwhile, computers are lack of processing capacity upon a large number of
model data. Therefore, resolving the conflicts between limited processing capacity of
computer and massive data of model is valuable. By investigating the characteristics
of
buildings
and
the
regular
changes
of
viewpoint
in
virtual
3D
environment,
this
article
introduces
several
constructing
rules
and
scheduling
techniques
for
3D
constructing of buildings, aiming at the reduction of data volume and complexity of
model
and
thus
improving
computers’
efficiency
at
schedul
ing
large
amount
of
architectural models. In order to evaluate the efficiency of proposed constructing rules
and scheduling technology listed in the above text, the authors carry out a case study
by 3D constructing the campus of Peking University using the proposed method and
the traditional method. The two results are then examined and compared from aspects
of model data volume, model factuality, speed of model loading, average responding
time
during
visualization,
compatibility
and
reusability
in
3D
geo-visualization
platforms: China Star, one China’s own platform for 3D global GIS manufactured by
the authors of this
paper. The result of comparison reveals
that models built
by the
proposed methods are much better than those built using traditional methods. For the
constructing of building objects in large-scale scenes, the proposed methods can not
only
reduce
the
complexity
and
amount
of
model
data
remarkably,
but
can
also
improving computers’ efficiency.


Keywords:

Constructing rules, Model scheduling, 3D buildings





















I. INTRODUCTION
In
recent
years,
with
the
development
of
3D
GIS
(Geographical
Information
System)
software
like
Google
Earth,
Skyline,
NASA
World
Wind,
large-scale
3D
building
models
with
regional
characteristics
have
become
important
form
of
geographic data beyond conventional 2D geospatial data, like multi-resolution remote
sensing
images
and
vector
data
[1].Compared
to
traditional
2D
representation,
geographic
information
can
be
expressed
in
a
more
intuitive
and
effective
manner
with architectural models being modeled and visualized in a virtual 3D environment.
3D
representation
and
visualization
provides
better
visual
effect
and
vivid
urban
geographic
information,
and
thus
plays
an
important
role
in
people's
perceptions
of
their environment. Meanwhile, the 3D building data is also of great significance for
the construction of digital cities.
But how to efficiently visualize thousands of 3D building models in a virtual 3D
environment
is
not
a
trivial
question.
The
most
difficult
part
of
the
question
is
the
conflicts
between
limited
processing
capacity
of
computer
and
massive
volume
of
model data, particularly in the procedure of model rendering. Taking the 3D modeling
of a city for the example using traditional 3D modeling method, suppose there are 100
000 buildings to model in the urban area and the average size of model data for each
building
is
roughly
10
M.
So
the
total
data
volume
of
building
models
in
the
city
could reach a TB level. However, the capacity of ordinary computer memory is only
in
the
GB
scale.
Based
on
this
concern,
the
authors
proposed
the
scheduling
technology
for
large-scale
3D
buildings
models
in
aspects
of
model
loading
and
rendering.
Due
to
the
lack
of
building
constructing
rules
and
standard,
models
of
buildings vary in aspects of constructing methods, textures collection and model data
volume, especially in aspects of model reusability and factuality. Such a large amount
of data without uniform constructing rules becomes a huge challenge for data storage,
processing
and
visualization
in
computers.
It
also
brings
the
problem
of
incompatibility among different 3D GIS systems.
After
years
of
research
in
GIS
(Geographic
Information
System),
people
have
accumulated a number of ways to solve the above problems [3]. However in virtual
3D
environment,
because
of
the
difference
in
data
organization
and
manners
of
human computer interaction (HCI), we need to apply a new standardized method of
modeling
and
scheduling
for
3D
models.
At
present,
there
is
no
such
a
uniform
method as the constructing specification or standard for the modeling of 3D buildings.
Existing
approaches
are
insufficient
and
inefficient
in
the
scheduling
of
large-scale
building
models,
resulting
in
poor
performance
or
large
memory
occupancy.
In
response to such questions, the authors proposed a new method for the construction of
3D building models. Models built using the proposed methods could be much better
than those built using traditional methods. For the 3D modeling of building objects in
scenes
of
large
scale,
the
proposed
methods
can
not
only
remarkably
reduce
the
complexity
and
amount
of
model
data,
but
can
also
improving
the
reusability
and
factuality
of
models.
Concerning
the
scheduling
of
large-scale
building
models,
the
Model Loading Judgment Algorithm (MLJA) proposed in this paper could solve the
optimal
judgment
problem
of
model
loading
in
3D
vision
cone,
particularly
in
circumstance with uncertain user interactions.
This
paper
first
examines
and
analyzes
existing
problems
in
constructing
and
scheduling
steps
of
3D
building
models.
Then
the
authors
propose
a
set
of
constructing
rules
for
3D
building
models
together
with
methods
of
model
optimization.
Besides,
special
scheduling
technology
and
optimization
method
for
model rendering is also applied in this paper for large-scale 3D building models. In
order
to
evaluate
the
efficiency
of
proposed
rules
and
methods,
a
case
study
is
undertaken by constructing a 3D model for the main campus of Peking University and
Shenzhen
using
both
the
proposed
method
and
the
traditional
method
respectively.
The
two
resulting
3D
models
of
Peking
University
campus
and
Shenzhen
are
then
examined
and
compared
with
one
other
in
aspects
of
model
data
volume,
model
factuality,
speed
of
model
loading,
average
responding
time
during
visualization,
compatibility
and
reusability
in
various
3D
geo- visualization
platforms
like
China
Star
(one
China’s
own
platform
for
3D
global
GIS
manufactured
by
the
authors),
Skyline,
etc.
Result
of
comparison
tells
that
provided
similar
factuality
of
models,
using the proposed method of us, the data volume of models was reduced by 86%; the
speed of model loading was increased by 70%; the average responding time of model
during
visualization
and
interaction
speed
was
reduced
by
83%.
Meanwhile,
the
compatibility
and
reusability
of
3D
model
data
are
also
improved
if
they
are
constructed using our approach.
II. MODELING RULES OF 3D BUILDINGS
3D
scene
is
the
best
form
of
visualization
for
digital
city
systems.
While
constructing
3D
models
for
buildings
objects,
proper
methods
and
rules
should
be
used, which are made with full concerns of the characteristics of 3D building models
[2].
The
resulting
models
should
be
robust,
reusable
and
suitable
enough
for
transmission
over
computer
network,
and
should
at
the
same
time
be
automatically
adapted to system capability.
Generally
speaking,
methods
of
constructing
3D
building
models
can
be
classified into three types: wireframe modeling, surface modeling and solid modeling.
In normal circumstances, to model buildings in 3D format, the framework of building
should be constructed first according to the contour features, number of floors, floor
height,
aerial
photograph
and
liveaction
photos
of
buildings.
Then,
gather
the
characteristics
of
scene
that
the
buildings
to
model
are
representing.
Important
characteristics
include
buildings
aerial
photograph
or
liveaction
shooting
photos.
Finally, map the gathered texture to model framework, optimize the model and create
database of the 3D building models.
Although there have already been many approaches for the construction of 3D
building models, a unified modeling method and rules are still needed to improve the
efficiency,
quality,
facilitate
checking,
reusability
and
archiving
of
constructed
models. By investigating the characteristics of buildings, we found that buildings have
regular
geometric
solid
for
modeling,
similar
texture
on
the
surfaces
of
different
directions, high similarity in small-scale models of buildings, etc. According to these,
this
article
gives
a
discussion
on
the
modeling
rules
from
three
aspects,
including
constructing rules of the 3D building models, texture mapping rules of 3D building
models
and
optimization
method
for
constructed
models
based
on
mentioned
constructing rules.
A. Constructing rules of the 3D building models
The 3D building modeling refers to the procedure of representing true buildings
from the real world into computer in the form of 3D objects [4]. Human beings, as the
creator
and
at
the
same
time
potential
users
of
models,
play
a
key
role
in
this
procedure. People are different from each other in the understanding of the building
objects,
methods
of
modeling
and
the
software
tools
they
use
for
modeling.
Such
differences among people who carry out modeling work at the same time lead to the
3D
models
of
diverse
quality
and
low
efficiency.
So
the
3D
building
constructing
rules
proposed
in
this
article
become
necessary
and
helpful
to
solve
the
above
problems.
1) Combine similar floors as a whole and keep the roof independent
2) Share similar models and process the details especially
3) Constructing in the unit of meters
4) Define central point of the model
5) Unified model codes
6) Reduce number of surfaces in a single model
7) Reduce combination of the models
8) Rational split of models
B. Texture mapping rules of 3D buildings
Based
on
the
framework
of
3D
models,
we
need
to
attach
these
models
with
proper textures to create a better visualization effect for 3D buildings. The quality of
texture mapping has
a direct
impact
on the visual
effect
of the scene whiling being
rendered [5]. Since the graphics card of computer will load all the textures together
when rendering a model, texture mapping rules and the quality of the texture mapping
can directly influence the efficiency of rendering as well.
C. Optimization of models based on constructing rules
Based
on
constructing
rules
and
the
characteristics
of
3D
building
models,
the
authors
develop
a
software
tool
to
optimize
the
3D
building
models
automatically.
The optimizations impl
emented in the software tool contain the deletion of models’
internal
textures,
merging
adjacent
vertices/lines/surfaces,
removing
un- mapped
framework
and
so
on.
Besides,
the
software
can
enhance
the
shape
of
the
whole
model, texture position and model facticity in the procedure of model optimization.
III. SCHEDULING TECHNOLOGY OF LARGE-SCALE 3D
BUILDING MODELS
For the 3D visualization of large-scale architectural models, a series of measures
could
be
applied
to
ensure
the
efficient
rendering
of
models.
Important
measures
includes
the
scene
organization,
vision
cone
cutting,
elimination
of
textures
on
the
backside of models, Shader optimization, LOD Algorithm, math library optimization,
memory allocation optimization, etc..
How
to
display
thousands
of
3D
cit
y
buildings’
models
in
a
virtual
3D
environment
is
not
trivial.
The
main
problem
is
the
scheduling
of
models
[7].
It
determines when and which models to be loaded. This problem can be divided into
two smaller problems: Find visible spatial region of models in 3D environment, and
optimization method of model rendering efficiency.
A. Find visible spatial region of models in 3D environment
According to operating mechanism of computers during 3D visualization and the
characteristics of large-scale 3D scene, we need to determine the position of current
viewpoint first before loading signal models or urban-unit models. Then in response
to the regular changes of viewpoint in virtual 3D environment, the system will preload
the 3D model data into memory automatically. In this way, frequent IO operations can
be
reduced
and
thus
overall
efficiency
of
system
gets
improved.
A
new
algorithm
named MLJA (Model Loading Judgment Algorithm) is proposed in this paper in order
to find out visible region of models in the 3D environment. The algorithm integrates
the graticules and elevation information to determine the current viewpoint of users in
the
3D
space.
And
with
the
movement
of
viewpoint,
the
algorithm
schedules
the
loading of model correspondingly and efficiently.
B. Optimization method of model rendering efficiency
The scheduling method of large-scale 3D building models proposed above is an
effective way to solve the problem caused the contradiction between large model data
volume and limited capacity of computers. According to the algorithm, we can avoid
loading the whole large-scale 3D building models at one time for the sake of limited
computer
memory,
and
then
improve
system
efficiency
in
the
procedure
of
model
loading and abandoning. Due to the limited capacity of GPU and local video memory,
we need a further research on how to display the loaded model data in more efficient
manner.
In
the
remaining
part
of
this
paper,
the
authors
will
continue
to
introduce
several methods on the optimization of model rendering in the vision cone.
1) Elimination of textures on the backside of models
The
backside
of
the
3D
model
is
invisible
to
the
users.
If
we
omit
the
texture
mapping for the 3D model on the backside, the processing load of graphic card will be
reduced as much as at least 50%. Besides, according to an investigation on procedure
of actual model rendering, the authors found that on the backside of the 3D model, the
invisible
texture
is
rendered
in
a
counter-clockwise
manner
against
the
direction
of
eyesight, while the visible texture mapping is rendered in clockwise manner. So we
can
omit
the
rendering
of
models
which
is
intended
to
be
rendered
in

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