|
3D
GIS
A Technology Whose Time Has Come
Gary Smith and Joshua Friedman
The very first output from a GIS came from a line
printer attached to a large mainframe computer. Using
individual letters (e.g., “W” for water) or
over-striking letters, line printer grayscale maps began
to show the patterns and results of the first GIS
analyses. In these pioneering years, 3D presentations were
not viable due to the limitations of computer performance.
Fast-forward 30 years and we have the ability to create
dynamic 3D GIS presentations on laptop computers.
While it may be too early to herald the end of the
plotter in favor of a virtual display, it is very clear
that use of 3D GIS to illustrate and analyze our GIS data
is growing. Also likely to succumb to the power of the
virtual, 3D GIS displays are the static architectural
renderings used to present proposed developments. Figure 1
illustrates the power of 3D GIS in the visualization of a
proposed new office building.
For years, we in the GIS community have assumed
that everyone viewing our work understood the 2D display
of
information. In reality, we all
knew better and as those that have started using 3D to
present their analyses can attest, a virtual environment
is very convincing in public meetings. The world around us
is three-dimensional and it seems natural that
presentations of GIS data should move in this direction.
How many times have we looked at a zoning map forgetting
that zoning also has a height component? Transitioning to
3D GIS need not be an arduous task. Quite the opposite is
true. This article is a basic primer to help one get
started in the 3D arena.
Beginnings
Serious use of 3D in GIS started about five years
ago with products like Evans & Sutherland’s
RapidSite product (no longer available) and MultiGen-Paradigm’s
SiteBuilder 3D extension to ESRI’s ArcView. Both of
these companies are principally involved in the creation
of simulators and supporting software. They saw their
technology in GIS as a logical extension of their
expertise.
These and other products successfully delivered
compelling 3D presentations but their acceptance by the
greater GIS audience was limited. Arguably, the
introduction of ArcGIS version 9 with the 3D Analyst
extension has done more to fuel the growth of 3D GIS than
any other software release. Almost over night, thousands
of GIS users were given the capability to create 3D
presentations complete with realistic buildings, trees and
other landscape objects. ESRI was certainly not the first
to make this possible, but its market penetration and
number of installations stand to hasten the transition to
3D.
3D Analyst version 9 comes with an extensive array
of 3D symbols (buildings, trees, etc.) but does not
include software capable of building custom features. For
the creation of custom buildings, trees,
and landscape features, users must turn to other
third party software solutions. While this does add
slightly to the cost of getting started, GIS users will
find the exposure to software from other 3D environments
very stimulating and informative.
ESRI and 3D
When it was released earlier this year, the ESRI
software could import 3D features in OpenFlight (popular
in simulations), 3D Studio (popular in game, animation and
architecture) and VRML (popular on the Web) formats.
Within weeks of the official release of ArcGIS version 9,
@Last Software, maker of SketchUp software, and ESRI
released free plug-ins that enable SketchUp models to be
imported directly into 3D Analyst as either symbols or
multipatch features.
As a symbol, an object can only be used for visual
purposes. The multipatch is a shape type stored in an ESRI
shapefile. It can store attributes and participate in
geoprocessing operations as well as used as a symbol. In
short, a building model, imported as a multipatch, is a
feature just like a parcel polygon is a feature in a
parcel GIS layer. The multipatch may very well prove to be
the key format that allows virtual 3D objects to be
“smart,” just like all other GIS layers.
Within the past few weeks word has surfaced that
Graphisoft, maker of ArchiCAD, and ESRI have created an
interface for exchanging information between ArcGIS and
the Virtual Building environment of ArchiCAD. It seems
logical that other component building and design software
packages will soon follow. Many already export into one of
the supported file formats.
Working in 3D
Constructing a 3D scene is a delicate waltz between
the incorporation of extensive detail and the need to
maintain an acceptable level of computer performance. A 3D
GIS operates in a run-time environment just like the
computer games and simulators. This environment allows
users to travel anywhere in the scene at any time. This is
in stark contrast to the animation quality movies that can
take hours to render single frames and only follow a
specified tract.
To create an efficient 3D environment, buildings
may be constructed as a wire frame and textured with
digital images to dramatically reduce the number of
polygons drawn by the computer without losing their
character and visual appeal (Figure 2). Careful use of
shadows can provide the illusion of detail in the building
model.
Building Trees
Tree models are usually composed of two or more
intersecting polygons with a picture of a tree pasted on
all sides. However, for trees that will only be viewed
from a distance, a single polygon that uses a lower
resolution photo will provide the same visual effect while
reducing the graphic impact of the scene. Figure 3
illustrates the construction of a green ash tree for use
in a 3D GIS environment.
More 3D visualization environments now support
models or symbols that incorporate levels of detail (LOD),
which can help improve performance while mimicking what
can or cannot be seen with the human eye. For example, a
model of a road sign built with LOD might use a detailed
texture at close range but switch to simple colors when
viewed from a significant distance.
Creating a tree model is actually much harder than
it looks. The process of extracting a tree from a full
digital picture to create a texture can be a time
consuming process. Issues of lighting, feature extraction,
size and formatting can account for hours of work. Years
ago a French company, Bionatics, recognized the tedious
nature of virtual tree creation and sought a mathematical
solution to this process. The result was a product called
RealNAT that has largely replaced manual tree model
creation within the simulator industry. Working from a
mathematical seed that is species specific, the software
grows trees to a specified age and seasonal depiction.
Saving a tree at different ages or seasons allows for a
temporal display that can illustrate change over time.
Seeds can be used over and over again, each time producing
a slightly different appearance.
Taking 2D GIS to 3D
Building an existing GIS database into a 3D
environment might seem like a daunting task. Attempted all
at once, such an undertaking might prove overwhelming.
Incremental work and concentration on important regions
can lessen the data development effort. Commercial growth
centers, downtown redevelopment areas and critical visual
resource areas are all logical starting points for
building 3D scenes that could ultimately cover an entire
GIS database.
New technologies like the High Definition Survey (HDS)
equipment (also known as 3D laser scanning) appear to
offer a substantial time saving method to capture the
“as built” environment. HDS is a LiDAR scanner on a
tripod and the points it generates from its laser striking
objects can be used to construct existing features.
3D GIS: Future Vision
Imagine a public meeting where a proposed building
is added to a virtual, GIS-enabled landscape. The GIS
immediately evaluates the new building for compliance with
use constraints as well as setback and height
restrictions. The water and waste water systems are
connected to the outside lines (GIS layers) to verify
capacity availability. Stormwater run-off from the roof
and other new impermeable surfaces are evaluated and
summarized. Security and emergency vehicle access
(including turn around space) are considered from all
access routes. Finally, the reviewers can evaluate the
appearance and compatibility of the new structure from any
vantage point within the existing virtual environment. By
substituting larger tree models for the initial planting
stock, it is possible to anticipate the appearance of the
area at some time in the future.
Consider an untapped resource—high school CAD and
computer animation students who might jump at the chance
to create 3D environments. For years the geospatial
community has worked to bring GIS to the K-12 age group.
This audience has grown up with computer games and the use
of 3D game-like environments to facilitate learning and
community involvement would seem like a natural match. Let
them help create the 3D environment from field
measurements and then enjoy the fruits of their labors.
Expect the opportunities for employing 3D GIS
technology to expand at a rapid rate over the next few
months and years. Officials are already looking at 3D
buildings by floor or even by room in applications related
to security and emergency planning. Figure 4 shows the
first floor of a school as a multipatch feature with the
roof and second floor turned off in the display. With
detailed terrain and land cover information can we better
model both the visual impact and performance of proposed
wind turbines on our hillsides? Viewsheds from the windows
of both existing and proposed buildings are now possible
in both in a quantified and visual simulation. In reality
we have just brushed the surface and exposed only a
fraction of other possible technologies that may be
applicable to GIS.
About the Authors
Gary Smith and Joshua Friedman are part of Green
Mountain GeoGraphics, Ltd. a GIS consulting firm that was
founded in 1988. They have been working extensively in 3D
GIS for more than six years and publish an informal 3D GIS
newsletter targeted at the users of ArcGIS and related
technologies. They can be reached at www.gis-help.com
or [email protected].
Back
|
