Buildings and Cities

Subsections:

• Roofs
• Procedural Building Implementations
• Academic Papers and Projects
• City Modelling Consulting and Services
• Commercial Sources of Building Data

Location

• There is no standard source or format, neither commercial nor free, for building footprint locations.
• ESRI Shapefiles or other GIS formats are often used for this purpose, but there is no standard for attributes.
• There is a lot of academic work, and some commercial tools, in extracting footprints from aerial photographs, but quality of automatically-extracted data is low, so it always comes down to manually digitizing each building.
  DRG
  
  DLG
• Classic USGS printed topographical maps ("topo quads") generally contain a black square symbol for every building (outside of urban areas).  This is sometimes (rarely) also digitized as a point feature in the corresponding DLG file.  However, for the most part, the USGS does not distribute the building locations in any digital point format - only as printed maps or DRG (scanned printed maps)
• USGS DRG
  •  Small buildings in low-density areas are shown as a single square black points, and large landmark building footprints are as shown as a black areas.  However, the rest of the buildings in high-density areas are not indicated at all.
  • Often, a revised map will show newer buildings in purple, instead of black.
• USGS DLG
  • Some topo maps have had their building information extracted (as points and polygons) as the "Manmade Features" layer of a DLG dataset.
  • When taken from the usual 1:25,000 scale topo maps, these general lack sufficient accuracy for realistic visualization - as well as lacking all attributes beyond footprint.
• OpenStreetMap supports building footprints (see VTP notes on OpenStreetMap)

Description: Parameterization

• a fundamental question is: what attributes of a actual building should be stored to describe it well enough so that a procedural construction approach can generate a acceptable visual reproduction?
• more simply: how do we describe a building's appearance succinctly?
• there are difficult trade-offs between representations which are fully flexible enough to handle any kind of structure, and those which are quick and easy for people to use
• Michael Flaxman's insightful notes on this subject
• subsection on Roofs
• it would be great to take advantage of the existing vocabulary of architecture
  • Illustrated Architecture Dictionary is a great resource with pictorial description of a huge number of terms, like "Apse", "Peristyle", and "Spandrel"
  • it also has an illustrated guide to 28 Styles of Architecture (primarily American)

Description: Classification

• for some uses, it is necessary only to classify each building into a fixed number of types
• these may be based on appearance (visual form), on use, or several other criteria
• UK aerial photo vendor The Geoinformation Group sells building data with either 72 or 45 building class codes (but doesn't list what those codes are?)
• SEDRIS has a number of military-oriented Classification Codes (part of EDCS) which can be used for buildings, but these are much more based on use (e.g. Community Recreational Facility) than structure or appearance
• the Getty Art & Architecture Thesaurus contains a ontology for building classification, although it is difficult to browse
  • relevant entries: definitions for buildings and Single Built Works
• there is a VTP attempt at a general culture classification which includes buildings

VTP Implementation

• in short, the VTP provides a representation for built structures, including buildings and linear structures such as fences, with a corresponding file format VTST, based on GML: see Buildings implemented in the VTP Terrain Library
• for examples of some issues that arise in the use of the VTP building implementation, see Using Virtual Cities to Plan Real Cities: A Case Study (August 2002, PowerPoint, 4 MB)

CityGML

• CityGML is an application profile for GML3 which encodes a multi-level representation of "cities".
• "City" is broadly defined to include not just built structures, but also elevation, vegetation, water bodies, and more.
• A project of SIG 3D, a consortium of several dozen German entities both public and private.
• There is a strong emphasis on LOD, with higher-level information about the objects.
• There is a free CityGML Viewer Application called Aristoteles, implemented in Java3D.
  • Tried version 0.8.4 in Sept. 2005, and learned that it requires the DirectX version of Java3D; the OpenGL version shows a blank window.  Using Aristoteles to view CityGML example files worked, although there were issues with textures glitches.
• Looking at the XML data, it appears that GML entities are used to describe the faces of the 3D model (!) which is wildly inefficient.
• Another viewer is the LandXplorer CityGML Tool
  • a restricted free version of LandXplorer Studio
  • free download, 21 MB, which includes a few sample files, very plain with no textures
  • the viewer does very little, just orbit and browse the XML tree
• Another is 3DGIS Cityvu, implemented in Java3D
  • Tried version 0.9.6.3 in July 2009.  It failed to load any of the city models available to me.  This underscores the interoperability problems of large, multi-level formats, of which readers and writes implement different subsets.

OpenBuildingModels

• OpenBuildingModels is a project begun in 2012 at a German university to augment the OpenStreetMap database with an open catalog of gelocated 3D building models.
• Looking at the first examples (in the town of Heidelberg), they are VRML files (.wrl)
  • The coordinate system is odd; the .wrl file has many nested transforms with very large values (far from the origin) which makes it jitter when viewed in Cortona; it's unclear whether the values are geographic, or in what units.

IFC/ifcXML/aecXML/etc.

• There are a number of other attempts at standardization of descriptions of buildings.  The purpose is to provide better interchange than just a DXF which contains drawings, but no higher-level information.
• The Industry Foundation Classes (IFC) is an open, object oriented file format with a data model developed by the IAI to facilitate interoperability in the building industry.  The actual IFC spec is on the IAI buildingSmart site, and there are example files available.
•  There is some overlap between IFC and another spec, aecXML, and overlap between both of them and CityGML.  There is even another sub-project IFG (IFC for GIS) which apparently overlaps with OGC standards and ESRI Data Models.

Materials

• There are many sources of texture maps for building materials, but nearly all good collections are commercial and therefore non-distributable.
• Paul Bourke's textures page has some nice windows, doors, roofing, etc.
• Other free online sources from: 3D total, Blender Textures, Mayang's Free Textures, etc.

Airports

• see Airports and Airplanes: Leveraging the Flight Simulation Field
• airport runways in the U.S. are included in the DLG transportation files, layer 1
  • however, they are only boundary lines, not polygons (is this correct?)

Building-specific Commercial Software

• Nverse Photo
  • $2500 from Precision Lightworks; plugin for 3DS MAX and VIZ
  • "Make very large 3D city scenes from big aerial photos by tracing building footprints using only simple 2D interaction. Automatically creates the 3D blends and extrusions, and automatically creates texture maps."
  • the company also does 3D urban modeling as a service
• Canoma
  • A famous discontinued software package from 1999, Canoma was ostensibly for extracting any model from photographs, but in practice it was most useful for buildings.
  • Even years later (2007) many people were using it, as some feel there has not been any newer software which is as easy to use.
  • References:
    • Great Software from the Past - Canoma
• PhotoModeler
  • $1000 for Windows.
  • General purpose model extraction from photos, with modeling of built structures as a common use case - see their Architecture & Preservation examples
  • The process can be very labor intensive; for example, the cabin model shown here involved manually digitizing 351 points.
• EspaCity
  • A variety of tools and functionality for measuring spatial data like buildings, roads and terrain forms from digital aerial imagery.  This is a "semi-automatic" stereoscopic photogrammetry digitization process.  ESPA's other products also include tools to work with LIDAR.
• PhotoSketch
  • A plugin for Google SketchUp, $350 commercial, $50 academic, 30-day trial
  • From the demo video, it appears that a large number of common features are automatically extracted from a series of photographs, then the geometry is identified manually by connecting those 3D points.  It look laborious, but perhaps not so bad after much training.

Games

• The console title The Getaway (2003) included some of the most impressive city modelling to date, apparently the result of several years of hand-modelling by a large team of modelers, resulting in a reproduction of a large part of London (!), yet fitting within the limitations of the Playstation2.

Furnishings

• eventually, a modelled building needs to be filled with appropriate furnishings
• in addition to plentiful sources of pre-made models, there are also some sources of parametric objects, though only GDL:
  • Objects Online - Your Online Object Library!

Tower Structures

• How Water Towers Work
• New York City Water Towers