Optical distance measurement

Various methods such as photogrammetry, triangulation, holography or time-of-flight measurements have become established for the optical 3D measurement of objects in space.

The distance measurement by means of time-of-flight measurement of laser light is the method we use most frequently. In the range of a few centimeters up to several hundred meters it is the method of choice when high accuracy and measuring speed have to be achieved even under difficult and changing environmental conditions. To measure distances, light is emitted and reflected by the object. The distance between the measuring device and the target object can be determined on the basis of the speed of light and the measured time of flight of the light from the light source (emitter) to the object and back to the detector.

The light, in our case always laser light, is modulated in its intensity. We use both pulse time-of-flight and phase shift measurement methods, which complement each other well in their strengths and weaknesses.

phase shift measurement
© Fraunhofer IPM
The phase delay method provides high measurement accuracy in the millimeter or submillimeter range.
Laserscanner principle
© Fraunhofer IPM
A laser beam is deflected by a rotating mirror, thus measuring a complete profile. As the measurement platform moves forward, for example on a vehicle, a measuring helix is created that maps the 3D profile of the environment.


Pulse time-of-flight measurement

The pulse time-of-flight method (also called ToF - time of flight or LiDAR - light detection and ranging) delivers a strong signal and allows the detection of several objects positioned behind each other. For example, measurements can be taken through vegetation or fog. The measurement rates are in the kilohertz range and the distance resolution in the centimetre range. The measurement range extends to several hundred meters.

Phase shift measurement

In contrast to the pulse time-of-flight method, the phase shift method delivers very high measurement accuracies in the millimeter or even submillimeter range. Measurement frequencies of up to several megahertz at measurement distances of less than one hundred meters are possible. However, the signal is weak and only one object can be detected. Environmental influences such as rain are rather disturbing.

Eye-safe, independent of lighting conditions, scanning

Both measurement methods can be implemented eye-safe with laser class 1 and are completely independent of lighting conditions. This means that measurements can also be taken at night, in situations where camera systems reach their limits, for example.

If the laser beam is transmitted via a rotating mirror, not only a point but also an entire profile can be measured. This is the principle of a laser scanner.

Which method is best suited depends on the specific application. We will be happy to advise you and supply you with a tailor-made system for your application.


Our laser scanners

Many of our laser scanners are in use worldwide. The monitor railway lines, road surfaces or large construction sites.