Using the ‘Subtracto-Silhouette’ parametric view-shed method in structure planning and architectural design

Significant building silhouettes and city skylines are an important part of urban composition and contribute to a city’s identity. Pressure to accommodate higher population densities in the form of tower developments can threaten these silhouettes. This paper discusses a parametric view-shed design method for setting height restrictions or maximum building envelopes that maintain culturally significant silhouettes whilst allowing high density urban development. I describe the process of using digital special effects found in animation software reconfigured to create three-dimensional maximum planning envelopes. The technique called ‘Subtracto-Silhouette’ uses animated particle systems (normally used to simulate explosions), ‘shot’ from a specific viewing position, traced through vertices of a key building’s geometry, intersected with an extruded site boundary to create an envelope. Inside this envelope, a developer can build anything without affecting the silhouette of the building in question from the key viewing position. I demonstrate the ‘Subtracto-Silhouette’ technique by describing two case studies. Firstly I discuss input into a planning amendment for the City of Stonnington Forrest Hill Precinct in South Yarra in Victoria, where a three-dimensional planning envelope was generated to protect an historic silhouette of the adjacent Melbourne High School. The second study is an architectural proposal for the Flinders Street Station design completion where I show the technique used in both a preservation as well as generative manner. I discuss the results of the technique applied on both case studies, demonstrating its effectiveness in policy development with the resulting Amendment C58 for Forrest Hill and show how it can be used as an integrated part of schematic design process in the Flinders Street Station proposal.