Buildings in vtdata/vtlib

The vtdata library stores building descriptions with objects of the vtBuilding class.  vtlib's vtBuilding3d subclass implements the procedural construction of 3D geometry, using the vtBuilding properties.  vtStructureArray acts as a container for vtBuilding objects.

See: vtlib structure classes.

Building description

• Location (2D geographic point)
• Shape of footprint (rectangular, circular, or explicit polygon)
  • if rectangular: width, depth and rotation
  • if circular: radius
  • if polygonal: footprint polygon
• Color of walls / trim / roof (RGB values)
• Roof type (flat, hip, gable - currently hip and gable are only implemented for rectangular buildings)
• Trim/molding (true/false)
• Array of Level objects, each containing:
  • Number of Stories
  • Array of Wall objects, each containing:
    • # of Doors
    • # of Windows
    • Material type (plain, siding)
• Elevated (flag: either elevated or embedded)

The current implementation is capable of very rough "massing models" of buildings, but is not flexible enough to represent / visually reproduce most buildings, especially modern buildings, buildings with porches, or multi-level buildings of the sort found on slopes.

Arbitrary roof polygons

• Implementation of flat roofs for arbitrary polygons required the ability to render concave polygons, which OpenGL does not do.  So, a survey was conducted of available code for Triangulation of Simple Polygons.
• Implementation of hip/gable roofs for arbitrary polygons requires an algorithm for the straight skeleton (see page on Roofs)

Future

• desirable parameters:
  1. relationship of  the building's ground floor to the terrain (embedded or elevated)
     • elevated houses might have options on how they're raised - beams, lattice, cement blocks, etc. - or this could be handled by the same mechanism used by the above-ground walls
     • there is a region around the building, associated with the building, in which the terrain is to be flattened ("terraffected")
  2. roof material (shingles, curved tile, etc.)
  3. a footprint for each story, would allow the shapes of most large city buildings
  4. height for each story
  5. presence of awning (true/false) - or this could be handled by roof outlines per floor
  6. roof pitch (angle)
  7. roof overhang (length)
  8. roof fascia height / molding
• long-range desirable:
  1. style/size of door
  2. style/size of window
  3. more complicated building shapes
     • how can these be described in simple terms?
     • perhaps the concept of shape grammars could be leveraged
     • one option: 
       • a footprint for the roof of each floor
       • walls represented as either as a footprint, or more flexibly, as a set of open polylines, each with its own wall style (railing, glass, etc.)
  4. dormers
  5. half-stories (areas formed by steep roofs, often extended by dormers to create usable space)
  6. higher-level descriptors, such as architectural style, which could provide a template which supplies default values
• a design goal: the description should be expressible in simple, spoken language.  that way a person could create the database with direct observation and speech recognition.

File IO

• vtStructureArray contains an array of  vtStructure objects and can read and write itself to the VTST file format

Discussion

• building chat with Roger James, 2003.03.18
• building chat with Roger James, 2003.04.08