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What Data Is Collected?

After an environment is measured according to the parameters, the user can select ``Save'' from the menu. Five files are written. They are:

1.
An IVR file that contains some of the parameters of the scan (HFOV and VFOV). This file is in a format that allows panoramic plug-ins[*] to web-browsers[*] to immediately display (pan, zoom) the reflected-light data collected.
2.
The reflected light image. This image is surprisingly good, simply showing the signal strength of the laser at each pixel. It has some strange characteristics since the projection is spherical, the light is infrared and the source of illumination is at the sensor (no shadows).
3.
The ambient light image. Similar to above, but contains the level of light subtracted from the incoming signal to identify the AM laser signal. Since we have an IR filter, this signal is usually very dark. It is used to determine sensor-overload (if the sensor is aimed at the sun, for instance).
4.
The distance image. This is written in 2 forms, one for visual inspection (scaled as a gray map from 0 to 255), and the other as the actual floating-point values.
5.
The RTPI file. This file is the most useful, but most difficult to use. The above files all involve interpolation fitting the data on a regular grid, while this file contains the raw data. There is a header with the number of columns scanned, followed by an integer for each column indicating the number of valid readings in that column, followed by the range, theta, phi, and intensity values (all floats) for each reading. The range is in inches, theta (angle around azimuth) and phi (angle above horizon) are in degrees, and the intensity is from 0 to 255.

The RTPI data are not on a regular grid, their position is our best estimate of the actual location of the device when the sample was taken. This includes compensation for the panning motor (correcting theta), since it can only move to one of many discrete positions.

Samples of the reflected light and gray-map distance images are shown in figure 1. The majority of the other figures shown in this paper are from reprojections of the RTPI data converted to Cartesian coordinates.


next up previous
Next: Sample Data Sets Up: Range Acquisition Software Previous: Collecting Data
Lars S. Nyland
1999-02-19