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Wall Grammar for Building Generation

Mathieu Larive and Véronique Gaildrat

Visual Objects, from Reality To EXpressionhttp://www.irit.fr/-Equipe-VORTEX

Oktal Synthetic Environmenthttp://www.oktal-se.fr

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Contents

• Introduction

• Frontage Templates

• Groundwork and Roof Templates

• Results and Discussions

• Conclusion and Future Work

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Problem

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Goals

• Quickly create a plausible (geo-typic) city around an already modelized zone (geo-specific)

• Reach a level of detail satisfactory enough for a navigation at ground level:– modeling of the buildings’inside– geometric modeling of the urban furniture

→ usage of automatic techniques inside AGETIM

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Generation steps

• Hierarchical division of city generation process in seven steps [Larive2005]

• Each step can be seen as a logical LoD

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Contents

• Introduction

• Frontage Templates

• Groundwork and Roof Templates

• Results and Discussions

• Conclusion and Future Work

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Frontage Templates

• A frontage template contains a primary wall and possibly a background material

• A frontage template can be seen as a style sheet that describes:– wall rendering– possible dimensions and kinds of windows and doors

(described as textures or 3D objects)– how to place these elements on the building

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Frontage Templates

• Formal grammar representation [Wonka2003]

• 2,5 dimensions paramatric wall grammar

Position rulesRepetition rules

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Frontage Templates

• Wall Panel

– the unique terminal symbol of our grammar

– various parameters:• texture

– Background– Decoration

• 3D object• possible dimensions

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Frontage Templates

• Extruded Wall– depth (positive or not)– depth faces generation

boolean – EW → W

• Bordered Wall– four margins– resize policy– BW → W

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Frontage Templates

• Wall Grid– Contains an unique

child wall– Repetition

• Vertical• Horizontal• Both

– Controlled by two cardinality intervals

– WG → Wnm

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Frontage Templates

• Wall List– Several child walls– Orientation (exclusive)

• Vertical• Horizontal

– WL → W1W

2...W

n

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Frontage Templates

• The combination of those different walls in a tree-like hierarchy allows the user to build simple or complex frontage templates

• Use of repetition schemes on every part of our frontages (wall grid)

• Usage of previously generated 3D objects (such as balconies or cornices)

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Frontage Templates

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Contents

• Introduction

• Frontage Templates

• Groundwork and Roof Templates

• Results and Discussions

• Conclusion and Future Work

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Groundwork and Roof Templates

• Groundwork templates– Z-min– Z-max– Extruded

Z-min Z-max Extruded

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Groundwork and Roofs Template

• Roof templates– Based on the Straight

Skeleton method [Felkel1998]

– One, two or four slopes– Overhang (4 types)– Currently, 10 various

roof types

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Contents

• Introduction

• Frontage Templates

• Groundwork and Roof Templates

• Results and Discussions

• Conclusion and Future Work

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Results

• Various buildings on one building footprint

94 faces 350 faces 5600 faces

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Results

• Large scale urban area

17 362 buildings, 920 182 faces generated in less than 8 mn

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Conclusion

• Able to generate buildings on any kind of footprint– convex, non-convex, non-plane, even with holes

• Generated buildings are valid – geometrically (no hole, no overlapping face, no empty

frontage -blind frontages-)– no window or door on a frontage edge

• Once a building template is finished and robust, it can be immediately reused (ready-to-use building template library)

• Control of the geometric complexity, according to the user hints

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Future Work

• Finalize the building template editor

• Usage of the Urban Land Use Model– Road network generation– Creation of lots and

building footprints

• Integration of all the various generation steps inside the same process