3D Isovist New algorithm

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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

[email protected]

[email protected]

[email protected]

15th International Symposium on Spatial Data Handling (SDH) – August 2012 in Bonn, Germany

mailto:[email protected]











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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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Definition

■ The free segment is a segment whose the two ends are visible

by the observer.

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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 Implementation : virtual environment on Matlab

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New algorithm for 2D ISOVIST Implementation : real GIS data on Matlab

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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


Isovist

The projection on the unit sphere centered at the observer point.

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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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Definitions

■ The free vision field is a solid angle of vision where no obstacle

is blocking the line of sight.

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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


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


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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 !






3D Isovist New algorithm

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