Sensing Modes

This page discusses various sensing modes that a Robotic Explorer or Web App might use.

Inertia, etc.

Acceleration, in physics, is the rate of change of velocity of an object. Using numerical integration, a computer can transform a series of acceleration measurements into velocity, displacement, and position. Obviously, this is an extremely useful type of information.

Because most mobile devices (e.g., smartphones) contain accelerometers, acceleration data is readily available. However, results of long-term integration tend to accumulate error. So, other input(s) are needed to adjust and/or confirm the user's position.

Of course, there are other measurements that might be of interest. Adafruit's 10-DOF "inertial measurement unit" is pretty amazing: it provides barometric pressure/altitude, temperature, and three axes of accelerometer, gyroscopic, and magnetic (compass) data. I'm not sure which of these we want (let alone need), but for $29...


Microwave is a form of electromagnetic radiation with frequencies between 300 MHz and 300 GHz. It has relatively short wavelengths (100 cm to 0.1 cm) and is highly directional.


The Global Positioning System (GPS) is based on satellite-based microwave beacons. Using precise timing information, the GPS receiver determines its distance from several satellites. Consumer-grade receivers do not have sufficient resolution to be of much use for finding walking paths, etc. More critically, they do not function well (if at all) within metal-laden institutional buildings.


Radar is based on microwave echolocation. Issues of power, safety, and weight make it poorly suited to use by a walking human. In addition, Radar does not work well for small distances, because of the (very small) echo latencies.


UHF ("Part 6") RFID operates at the lower end of the microwave region (e.g., 433 and 856-960 MHz). Passive tags can be detected within 12 meters; active tags can be detected within 100 meters. When the tag is activated, it can emit a data string such as a globally unique ID (e.g., IRI, UUID). Although RFID detection is not inherently directional, it should be possible to calculate a vector to the tag using one or more directional antennas. For more information, see my RFID page.


Odometry is the use of data from motion sensors to estimate change in position over time. Odometry is used by some robots, whether they be legged or wheeled, to estimate (not determine) their position relative to a starting location. This method is sensitive to errors due to the integration of velocity measurements over time to give position estimates. Rapid and accurate data collection, equipment calibration, and processing are required in most cases for odometry to be used effectively.

-- Odometry (WP)

When a robotic explorer is rolling along, its wheels are (in general) rotating. By recording the amount of rotation for each wheel, we can estimate the distance traveled, etc.


Ultrasound is a form of acoustic radiation with frequencies higher than the upper limit of human hearing (e.g., 20 kHz). It has relatively short wavelengths (e.g., less than 2 cm) and is highly directional.

It should be possible to create Reflective Markers that (a) reflect ultrasound very well and (b) produce a distinctive acoustic signature. This could be used to identify the locations of waypoints.

Distance Sensors

Ultrasonic distance sensors are readily available, For example, the MaxBotix MB1360 has a precision of 1 cm at ranges up to 10 meters. It emits a sound, then captures timing and amplitude data. This can be used to calculate distances, estimate object sizes, etc.

The Sonic Eye

The Sonic Eye is a proposed navigational aid for the blind and visually impaired. It is based on biomimicry of the animal echolocation performed by microbats. It emits a rising-frequency chirp, receives the echoes with a pair of specially-shaped pinnae, and presents a time-expanded binaural version to the human listener.


The rising frequency of The Sonic Eye's chirp is a simple form of frequency modulation. Because each frequency corresponds to a a transmission time, the listener can determine when the original signal (for a given echo) was sent.

Digital modulation schemes (e.g., PCM) can be used in a manner analogous to GPS. So, they can identify the sender, provide timing information, etc. See my Modulated Ultrasound page for details.


Light is a high frequency (and thus highly directional) form of electromagnetic radiation. Visible light is usually defined as having wavelengths in the range of 400–700 nanometers (nm). Visible light can be used by both cameras and eyes; infrared and ultraviolet light can be used by cameras, etc.


Laser-based tools can be used to measure and record distances. They can also be used (in the form of Lidar) for mapping. However, beaming lasers around occupied areas is both rude and unsafe. So, not going there...


Although computer vision systems can recognize some objects in images or video streams, recognizing arbitrary objects seems to be an AI-complete problem. Even gathering information about walls (e.g., angles, distances) appears to be challenging. So, not going there...

QR codes

QR codes are two-dimensional barcodes that employ forward error correction. Using a typical cell phone camera, a QR code can be read if its width exceeds 10% of the distance involved. So, for example, to be readable across a 20' corridor, a QR code would need to be 2' wide. So, not going there...


Simple visual symbols (e.g., red octagon, yellow triangle) can be recognized at far greater distances than complex symbols such as QR codes. So, it might be possible to create a set of distinctive symbols that are easily recognizable by a camera. Small numbers of false positives are not a problem; they can simply be ignored.

Breakout Pages

This wiki page is maintained by Rich Morin, an independent consultant specializing in software design, development, and documentation. Please feel free to email comments, inquiries, suggestions, etc!

Topic revision: r86 - 25 Feb 2016, RichMorin
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