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3D Visibility with Vector GIS Data
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3D Visibility with Vector GIS Data

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The visibility estimation has an important impact in many economical and aesthetic fields, a mixed environment which contains madman objects like buildings with relief sol make a challenge for the …

The visibility estimation has an important impact in many economical and aesthetic fields, a mixed environment which contains madman objects like buildings with relief sol make a challenge for the visibility calculation. This paper presents a new method to solve this problem based on vector GIS data. The use of vector data gives the possibility to calculate the intervisibility, viewshed for mixed environment. The new method could identify the obstacles (relief, buildings identification) which block the visibility for a 3D environment points from observator, the intervisibility impact of a specific building could be calculated

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  • Fields of use economic 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 Installations positioning radio antennas, wifi access points, surveillance cameras, advertisement posters. Inter-visibility : 2 viewpoints connected by sight Isovist 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
  • Computing 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.
  • Vector Isovist is interesting because it can deal with man-made objects as buildings and can determine I a façade of a building can be seen from a view point or identify the building that blocks the intervisibility between two points. But Isovits face some difficulties when dealing with 3D environment composed of buildings laying on a non-flat topographical surface
  • Raster tools are not efficient with buildings. They add the building height to the DEM but the identity and the individuality of the entities (buildings for example) is lost.
  • Raster 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
  • An area in Saint-Etienne : 1 km², nombre de bâtiments ? 40 buildings, 233 polygones The 3D world becomes a list of polygon plane facets; each of these facets has a type (terrain, building) and an identification number that can refer to a triangle Id of the TIN or a building Id combined with a wall (facade) or a roof number.
  • A regular grid of view points is determined beforehand one point every 10 meters. The vertical offset of the grid point is a variable (1.60 m for the test) The points within the building can be eliminated or placed on the roof (depending on the objectives of the study : is the point on the roof a viewpoint ?)
  • Identification of every grid point, every 3d polygon (Tin ID) or (Building ID, facet ID)
  • Two points can see each other if the segment between them is not intersected by any plane surface (polygon) of the 3D environment. Reciprocity : if the point A can see the point B, then the point B can see the point A. Find if a polygon P block the intervisibility between two points from Segment S (Polygon P /Segment S ) intersection
  • Find Line / Plan intersection 3D
  • Test1 : if Intersection point in Polygon 2D
  • Test2 : if Intersection point on Segment 1D
  • In this calculation, a percentage of the visibility or a visibility coefficient can be assigned to every point of the grid (Turner et al. 2001) with the identification of points that could be seen from the considered point (Figure 8). The result is exported as a shape file of points.
  • An interpolation of the results is realised between the points of the grid in order to produce a continuous representation The intervisibility interpolated map using Inverse Distance Weighting (IDW), VisPersnetN is the visibility percentage, VisPointsIDC is the visible points IDs from the according point
  • The grid points are visible or not from the view points. The result is a shape file of points with a visibility data field that indicates if the grid point is visible or not. An obstacle data field lists the parts of the terrain or the buildings that block the view from the observer position
  • the target building is selected and the intervisibility effect of this building is calculated. The result is a shape file of the grid intervisibility points. A new attribute “Affected” is created in the table who indicates if the target building has or not an impact. If some points are affected, another attribute lists the hidden points due to the target building
  • The diminution of the size of the files (or the number of points) depends of the topography : if the ground is quite flat, we can reduce the points number up to 80% if there is a lot of slopes the reduction is about 40%
  • We reduce the points number for the polygon representation (30% - 60%) The simplifying of theses polygons is addressed in the literature as the model generalisation question (Favier 1994) (Anne Ruas 1999) (Qingsheng et al. 2002). In order to simplify the polygons of the buildings, extra collinear points are eliminated. Then the points that form a facade arc smaller than 2 metre long were removed from the polygon. The user can modify this value (
  • Pour calculer l'isovist 3D d'un point de vue donné, il me semble qu'on pourrait prendre à la place de la grille arbitraire, l'ensemble des sommets des polygones.

Transcript

  • 1. 3D Urban Visibility Analysis with Vector GIS Data SULEIMAN Wassim 1 , JOLIVEAU Thierry 1 , FAVIER Eric 2 1 ISTHME-ISIG CNRS/UMR EVS, Université Jean Monnet - Saint-Etienne. 2 DIPI EA 3719 École Nationale d'Ingénieurs de Saint-Etienne [email_address] [email_address] [email_address] 19th annual GIS Research UK (GISRUK) - University of Portsmouth - 27 th -29 th April 2011
  • 2. Visibility analysis
    • Fields of use :
      • Urban and landscape planning
      • Navigation systems
      • Visual surveillance
    • Measures in view assessment
      • Inter-visibility
      • Isovist and viewshed
      • Global visibility
  • 3. Main technique : ray tracing 2D Vector data 2.5D Raster data Brossard & Wieber
  • 4. 3D ? Wii home
  • 5. Entities ? Source : DSS for Coastal Protection Design by Cdr.Phinai Jinchai Public Eye
  • 6. One idea : 3D Voxel model Ray tracing (Pyysalo et al. 2009), (Morello & Ratti 2009)
  • 7. Another idea in vector mode
    • 3D environment considered as a constellation of polygons
      • TIN terrain model +
      • 2D footprints with
      • height extrusion
    3D polygon plane facets (terrain, building)
  • 8. A regular grid of viewpoints
  • 9. 3D Data Model building wall roof terrain facet view point
  • 10. Data and Tools
    • Data
      • Totopographic Database of IGN
    • Tool
      • Matlab
        • Easy of use
        • Rapid prototyping/debugging of sophisticated code
        • Tools for GIS data import and export from ArcGIS (Mapping Toolbox)
        • Tools for simulation and data analysis (Symbolic Math Toolbox, Parallel Computing Toolbox, Statistics Toolbox, Optimization Toolbox)
        • Easy rapid visualisation
      • ArcGIS
        • Interpolation, visualisation
  • 11. Principle of the computation
    • If Test1 and Test2 is verified then there is no intervisibility between the two points
  • 12. Principle : intervisibility between two points connected by a segment ?
    • Polygon / Segment intersection in the 3D environment ?
    Polygone Segment
  • 13. Step 1: Find the plan of the polygon and the line of the segment (3D) Plan Line
  • 14. Step 2: Find the Intersection point between the plan and line (3D) Plan Line Intersection point
  • 15. Step 3: Check if the Intersection point belongs to the polygon (2D) (Test1) Plan Intersection point Polygone
  • 16. Step 4: Check if the Intersection point belongs to the segment (Test 2) If the results of tests 1 and 2 are true, the segment and the polygon intersect. => the polygon blocks the visibility between the extremities of the segment Line Intersection point
  • 17. Global intervisibility results
  • 18. Global 3D intervisibility interpolated map
  • 19. Result : 3D Isovist calculation
  • 20. Building 3D intervisibility effect
  • 21. Order of complexity of the algorithm
    • Function of :
      • the number of the grid points
      • the number of the polygons in the 3D environment
    Necessity to reduce the number of the 3D polygon by simplifying the TIN model and Building
  • 22. Simplifying the DEM
    • Eliminating extra points in the same level (IsoLevel) within 1 m height interval parameter
    DEM DEM with IsoLevel simplification
  • 23. Simplifying the buildings polygon
    • The extra collinear points were eliminated
    Original building polygon Simplified building polygon
  • 24. Results of 3D simplification
    • The execution time is 2 times faster
    • Negligible change in the intervisibilty map and viewshed map (less than 5%)
  • 25. Future work
    • Vegetation layer
    • “ Real” 3D Isovist
    • Points on the building facades
    • More complex buildings models
    • Implementation in GIS software
    Decouvrir Arc de triomphe
  • 26. Thank You Images sources : Woo home : http://www.woohome.com/photograph/steep-hills-of-san-francisco DSS for Coastal Protection Design by Cdr.Phinai Jinchai http://www.dss4cpd.com/dmain/index.php?q=node/26 Public Eye : http://www.globalsecurity.org/eye/html/wtc_noaa_wtc3.htm Decouvrir Arc de triomphe : http://decouvrir-arcdetriomphe.blogspot.com/2011/04/quizz-anecdotes.html