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Abstract. Isovist or vision field computing is an interesting topic with many applications in different fields: security, wireless network design, landscape management. In all existing solutions, 3D environment appears to be the most challenging task and a few solutions exist for detecting the obstacles that limit the vision field. In this paper a new algorithm is presented for isovist calculation that can detect all the objects which block the sight in a 2D and 3D environment. Then a demonstration with GIS data is given. And some visibility indices are also presented.
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A New Algorithm for 3D Isovist
SULEIMAN Wassim1,
JOLIVEAU Thierry1,
FAVIER Eric2
1ISTHME-ISIG CNRS/UMR EVS, Université Jean Monnet - Saint-Etienne. 2DIPI EA 3719 École Nationale d'Ingénieurs de Saint-Etienne
15th International Symposium on Spatial Data Handling (SDH) – August 2012 in Bonn, Germany
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Isovist Isovist : the visible space from a given point in
space.
Fields of use :
■ Urban and landscape planning
■ Navigation systems
■ Visual surveillance
■ Publicity placement
■ Wireless Network architecture
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Main technique for computing Isovist :
ray tracing
2D Vector data 2.5D Raster data
Brossard & Wieber
Number of rays ? Resolution ?
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3D ?
Wii home
Challenge:
Dealing with 3D environment composed of buildings laying on
a non-flat topographical surface.
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2.5 and 3D Isovist solutions
Limitations ?
• The identity and the individuality of the special entities
(buildings for example) is lost
• The precision is related to the resolution
2,5 Raster mode
(Public Eye)Voxel mode
(Pyysalo et al. 2009), (Morello & Ratti 2009)
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New algorithms for computing ISOVIST
in 2D and 3D
The principle is to analyze how the spatial entities
(buildings) block the line-of-sight.
The isovist will be considered as a group of vision angle
associated with spatial entities or free space (if there
is no building blocking the sight).
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New algorithm for 2D ISOVIST
Assumption
■ 2D space is an aggregation of segments.
■ We will use the polar coordinates centered at the observer
point.
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New algorithm for 2D ISOVIST
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New algorithm for 2D ISOVIST
Definition
■ The free segment is a segment whose the two ends are visible
by the observer.
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New algorithm for 2D ISOVIST
Definition
■ The free vision field is an angle of vision where there is no
obstacle blocking the line of sight.
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New algorithm for 2D ISOVIST
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New algorithm for 2D ISOVIST Implementation : virtual environment on Matlab
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New algorithm for 2D ISOVIST Implementation : real GIS data on Matlab
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New algorithm for 2D ISOVIST
Application: dominant type of buildings in view
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3D data model used for implementing
the 3D Isovist algorithm
3D polygon plane facets (terrain, building)
3D environment considered as a constellation of
polygons
■ TIN terrain model +
■ 2D footprints with
height extrusion
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A new algorithm for computing 3D
Isovist
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Projection
Observer
Polygon
A new algorithm for computing 3D
Isovist
The projection on the unit sphere centered at the observer point.
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A new algorithm for computing 3D
Isovist
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A new algorithm for computing 3D Isovist
Definitions
■ The free polygon is a polygon whose edges (or the enclosed
frontier segments) are visible from the observer.
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A new algorithm for computing 3D Isovist
Definitions
■ The free vision field is a solid angle of vision where no obstacle
is blocking the line of sight.
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A new algorithm for computing 3D Isovist
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A new algorithm for computing 3D Isovist
Implementation on Matlab
Verification and validation: the comparison between our 3d isovist and the real
visibility
2D/3D registration
(Edges and corners matching)
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The image by
the 3D isovist
The image in
The real world
A new algorithm for computing 3D Isovist
Visibility of target building with IDW interpolationOpen sky index with IDW interpolation
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Visibility of target
building with solid
angle of vision
interpolation
Application: Computing visibility indices
A new algorithm for computing 3D Isovist
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Conclusion
We propose a new algorithm for computing Isovist in
2D and 3D environment with non-flat topographical
surface
It permits the calculation of classic visibility indices
and new ones like the content of the view (e.g. the
percentage of historic building in a view)
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Future work
Developing a stand alone program to achieve the
calculation.
Using parallel processing like using cuda over GPU.
Implementation in the hardware or in a low level
programming language.
Thinking about meaning and definition of 3D Visibility
indices (vertical and horizontal surfaces).
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Thank you
for your attention !
