3D Urban Visibility Analysis with Vector GIS Data

1A New Algorithm for 3D IsovistSULEIMAN Wassim1, JOLIVEAU Thierry1, FAVIER Eric2

1ISTHME-ISIG CNRS/UMR EVS, Universit Jean Monnet - Saint-Etienne. 2DIPI EA 3719 cole Nationale d'Ingnieurs de Saint-Etienne

wassim.suleiman@univ-st-etienne.fr thierry.joliveau@univ-st-etienne.fr eric.favier@enise.fr

SAGEO 2012 7 November 2012 in Liege, Belgium12IsovistIsovist : the visible space from a given point in space.

Fields of use : Urban and landscape planningNavigation systemsVisual surveillancePublicity placementWireless Network architecture

2Fields of useeconomic and aesthetic value of buildings is highly related to the visibility field that it could offer to its citizens It is important for urban planning or landscape planning. But visibiliy analysis can be useful in other fields as automotive navigation system for enriching Wayfinding Instructions with Local Landmarks or in planning and evaluating Coverage of Visual Surveillance Network Installationspositioning radio antennas, wifi access points, surveillance cameras, advertisement posters.

Inter-visibility : 2 viewpoints connected by sightIsovist and Viewshed : the area that could be seen from a viewpoint Global visibility : to quantify or evaluate the view of a large number of viewpoints : width, lenght, area, nature of what is seen

3Main technique for computing Isovist : ray tracing

2D Vector data

2.5D Raster dataBrossard & Wieber Number of rays ?Resolution ?3Computing Visibility uses mainly ray tracing. A virtual ray is thrown in the space and interfere with different spatial entities that block its way.Isovist is based on vector format : points and polygons. The observer is a point and a ray is thrown through space in different directions until it meets an obstacle. The area visibility for this point is defined by the vector polygon delimitated by the intersection points with the boundaries of this obstacles.. For global visibility, the isovist is calculated on a grid and for every point of this grid some indicators of the isovist are calculated (area, maximal length, orientation of the maximal length ) Viewshed is based on raster format. The observer point is a pixel and the area of visibility is defined as the subset of pixels that can see or the observer or be seen by it. In global visibility the characteristics of the viewshed of every pixel are calculated.

42.5 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) 4Raster oriented (extended method)3D-isovist-like approach (Pyysalo et al. 2009) (Figure 4) (Morello & Ratti 2009) The basic idea is to use voxel models[1] with adaptive transparency to add buildings and vegetation then to calculate the 3D isovist. Complexity depends of the ray tracing number and voxel numbers

and voxel numbers5New 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).6New algorithm for 2D ISOVIST Assumption2D space is an aggregation of segments.We will use the polar coordinates centered at the observer point.

7New algorithm for 2D ISOVIST

8New algorithm for 2D ISOVIST DefinitionThe free segment is a segment whose the two ends are visible by the observer.

9New algorithm for 2D ISOVIST DefinitionThe free vision field is an angle of vision where there is no obstacle blocking the line of sight.

10New algorithm for 2D ISOVIST 11New algorithm for 2D ISOVIST The complexity

For environnement with N 2D segments, the complexity is in order of N*log(N)

Comparison with ray tracing, for R ray tracing, The complexity is in order of (R+N)*log(R+N)

For precision of 10^-6 rad, we need R= 2**10^6 6,283,000 !!!1112New algorithm for 2D ISOVIST Implementation : virtual environment on Matlab

The result as series of an angular interval with visible segment in these interval 1213New algorithm for 2D ISOVIST Implementation : real GIS data on Matlab

Application on a real case with the visibilty polygon, with some morphometry mesurment like circularity, and we add on it the nearest point, the farthest point, the open view 1314New algorithm for 2D ISOVIST Autonome application using VB.NET langage

Execution time less than 10 secWe give a persantage of view for every type of commercial building1415A new algorithm for computing 3D Isovist 16ProjectionObserverPolygonA new algorithm for computing 3D Isovist The projection on the unit sphere centered at the observer point.

11617A new algorithm for computing 3D Isovist

18A 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.

19A 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.

20A new algorithm for computing 3D Isovist 21The complexity

For environnement with P 3D polygons the complexity is in order of P (3D segment polygon intersection)

Comparison with ray tracing, for R ray tracing, The complexity is in order of (R+P) (3D segment polygon intersection)

For precision of 10^-3 rad, we need R= (*10^3)*(2**10^3) 19,739,000 !!!A new algorithm for computing 3D Isovist 22A new algorithm for computing 3D Isovist Implementation on Matlab

Execution time about 2 minTest over a virtual cube, the results is a three surface over the unit spher related to the three visible face of the cube.

test in a real gis sample on the city, here we can see the visible faade from the observer point 22

23Autonome application using C# langageA new algorithm for computing 3D Isovist

Execution time less than 30 secSpace Syntax is a group of indices like visibility, openness ,enclosure and scale based on the calculation of isovist. Theses indices are proved to have a correla-tion with the human perception of the SEEN ENVIRONNEMENT.

The space syntax calculation starting with open space index;The visibility of a buildingThe visibility weighted with the view angle of visibility 2324Autonome application using C# langageA new algorithm for computing 3D Isovist

Space Syntax is a group of indices like visibility, openness ,enclosure and scale based on the calculation of isovist. Theses indices are proved to have a correla-tion with the human perception of the SEEN ENVIRONNEMENT.

The space syntax calculation starting with open space index;The visibility of a buildingThe visibility weighted with the view angle of visibility 2425Arcscene Addin to export the results in format Esri multipatchA new algorithm for computing 3D Isovist

Space Syntax is a group of indices like visibility, openness ,enclosure and scale based on the calculation of isovist. Theses indices are proved to have a correla-tion with the human perception of the SEEN ENVIRONNEMENT.

The space syntax calculation starting with open space index;The visibility of a buildingThe visibility weighted with the view angle of visibility 2526ConclusionWe propose a new algorithm for computing Isovist in 2D and 3D environment with non-flat topographical surface.The new algorithm is faster than usual ray tracing method.We develop a stand alone program to calculate the isovist in 2D and 3D with the possibility to export the result as Esri shape file like (points-polygons-3D multipatch). 27Future workUsing parallel processing like using cuda over GPU.

Thinking about meaning and definition of 3D Visibility indices (space syntax).28Thank youfor your attention !Suleiman Wassimwassim.suleiman@univ-st-etienne.fr 28