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.

1. 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
wassim.suleiman@univ-st-etienne.fr
thierry.joliveau@univ-st-etienne.fr
eric.favier@enise.fr
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15th International Symposium on Spatial Data Handling (SDH) – August 2012 in Bonn, Germany

2. 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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3. Main technique for computing Isovist :
ray tracing
2D Vector data 2.5D Raster data
Brossard & Wieber
Number of rays ? Resolution ?
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4. 3D ?
Wii home
Challenge:
Dealing with 3D environment composed of buildings laying on
a non-flat topographical surface.
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5. 2.5 and 3D Isovist solutions
2,5 Raster mode Voxel mode
(Public Eye) (Pyysalo et al. 2009), (Morello & Ratti 2009)
Limitations ?
• The identity and the individuality of the special entities
(buildings for example) is lost
• The precision is related to the resolution
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6. 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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7. 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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8. New algorithm for 2D ISOVIST

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9. 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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10. 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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11. New algorithm for 2D ISOVIST

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12. New algorithm for 2D ISOVIST
Implementation : virtual environment on Matlab
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13. New algorithm for 2D ISOVIST
Implementation : real GIS data on Matlab
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14. New algorithm for 2D ISOVIST
Application: dominant type of buildings in view
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15. 3D data model used for implementing
the 3D Isovist algorithm
 3D environment considered as a constellation of
polygons
■ TIN terrain model +
■ 2D footprints with
height extrusion
3D polygon plane facets (terrain, building)
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16. A new algorithm for computing 3D
Isovist

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17. A new algorithm for computing 3D
Isovist
The projection on the unit sphere centered at the observer point.
1
Polygon
Observer
Projection
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18. A new algorithm for computing 3D
Isovist

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19. 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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20. 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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21. A new algorithm for computing 3D Isovist

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22. A new algorithm for computing 3D Isovist
Implementation on Matlab
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23. A new algorithm for computing 3D Isovist
Verification and validation: the comparison between our 3d isovist and the real
visibility
The image by The image in
the 3D isovist The real world
2D/3D registration
(Edges and corners matching)
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24. A new algorithm for computing 3D Isovist
Application: Computing visibility indices
Open sky index with IDW interpolation Visibility of target building with IDW interpolation
Visibility of target
building with solid
angle of vision
interpolation
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25. 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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26. 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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27. Thank you
for your attention !
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