TAPESTRY: The Art of Representation and Abstraction
Data Types - Point Clouds
What's it all about?
While there are few sources of building-scale voxel data, there are surveying devices, mostly using laser beams, that can be stationed in one place, pointed at a building some distance away, and used to measure the distance from the device to the building, over and over again, with slight re-orientations between samples. What you learn from this is the distance to the building along a whole lot of lines of sight. If you know where your device was, each one of these (plus some trig) can give you the coordinates of a point in space. Collectively, you have a "cloud" of sample points, or a "point cloud".
Primitives
As with the voxels (and most automated data generation), there is only the one simple primitive: the location of a point in space. Anything else is a matter of interpretation (but see below).
Attributes
An exception to this arises when the scanning device also samples the surface's color at the point where the laser beam strikes. In that case the data may represent the location of a point in space, and it's color. If the points are close enough together, this will produce a color image of the surface in addition to location data.
Organization
As with voxel data, significant research and development effort has gone into creating algorithm's to extract (arbitrarily dense) polygon meshes from the point cloud. In the simplest case, you might connect each point to its two nearest neighbors, forming a mesh of triangles, but you'd really like to locate and identify architectural features, such as doors and windows, and it would be good to reduce the mesh covering a simple wall to just the four corners. This is an area of ongoing research.
Examples
Extracting surface or solid data from point clouds is possible, though often limited to fairly simple models in readily available software (Rhino or form•Z for example). Laser scanners (big or little) often include surfacing package to help. As the resulting surfaces are usually simple meshes, editing can be a challenge.
Last updated: April, 2014
