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Working with point cloud data
May 26, 2009

cloudTool Screenshot

Point cloud data is conceptually quite simple. There is no structure to the points; they all exist independently of each other in an unordered list. Each point is specified by three numbers indicating the distance from the Origin point which is simply written as (0, 0, 0). Each number indicates the distance from the origin along the x-axis, y-axis, and z-axis, written as (x, y, z). One of the axes (often z) is interpreted as the height so when this value is zero, the point is said to lie on the ground plane. The x and y values are typically used to represent the distance from the origin along the "length" and "width" on the ground plane. Each point can also have a color value associated with it, expressed as a combination of red, green, and blue values (that range from 0 to 1), written as (r, g, b). In our data set, the scanner returned only a reflectance value so this is stored as a grey value, or brightness. A grey color will have equal values for r, g, and b.

The point list format is six values (x, y, z, r, g, b) with one point on each line in a file. For example, if a point was ten units above the origin and was a mid-tone grey, the point data would be (0, 0, 10.0, 0.5, 0.5, 0.5). Above is some code is shown to read in the point list from a file. Using the QT user-interface framework, we have made a small program to read in the point list from a file (with a sample point cloud file from the 210 King lobby, as part of the downloads). The source code is provided, but there is also a Microsoft Windows sample application pre-built that can be run directly.

ZIP
CloudTool Binary and Source
ZIP - 4.950MB


ZIP
Lobby Scan Ascii Point Cloud
ZIP - 8.359MB


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