Mobile Laser Scanning (MLS) is one of the most advanced surveying techniques, to date. In many respects, MLS is like the widely used terrestrial laser scanning (TLS), but in contrast to the TLS, mobile scanning is performed by moving a vehicle-installed scanner. In this case, the surveying speed matches the speed of the vehicle, which is tens of kilometers per hour. No other method features a similar or even close performance in so far as related to the spatial data collection, with an absolute precision of a few centimeters. Only aerial photography and airborne laser scanning speed exceeds MLS data collection, however, it is much inferior in accuracy and detail (point density).

Mobile scanning system can be mounted on cars, ships, railroad cars and other vehicles. The scanning is performed along the trajectory with a several hundred meters in all directions distance. The density of points depends on the speed and range of the object, and can vary from a few to thousands of points per 1 square meter.

RieglVMX-250 installation in mobile scanning options RieglVMX-250 installation in mobile scanning options

RieglVMX-250 installation in mobile scanning options

Mobile scanning is successfully used wherever it is possible to pass for a vehicle access on which the system is installed: roads, railways, any waterways, industrial sites, city streets. The system can be installed on off-road vehicles and perform surveying in the absence of roads. MLS is also used in surveying tunnels in the roads and railway, as well as subway lines.

Mobile laser scanning can be performed as an independent operation, and combined with other types of surveying (TLS, ALS, classical geodetic surveying methods). "NIPIStroyTEK" has the most modern cutting-edge sensing equipment (hardware reference) in its possession. The surveying method and technology to be used is defined at the preparatory stage of each project on the case-by-case basis.


 MLS point cloud, colorized according to the photographic data.
 Surveying a residential area. Mobile and terrestrial laser scanning data (point cloud) combined.

MLS point cloud, colorized according to the photographic data.

Surveying a residential area. Mobile and terrestrial laser scanning data (point cloud) combined.

  Surveying a railway line with adjoining territory. Mobile and airborne laser scanning data (point cloud) combined.

Surveying a railway line with adjoining territory. Mobile and airborne laser scanning data (point cloud) combined.




Mobile laser scanning of a railway..

Mobile laser scanning of a railway: the Smolensk Railway station.

Main applications:

  • Roads and railways; Detection of road surface defects (rutting, the presence of pits and fissures, the actual transverse and longitudinal slope of the roadway), creating three-dimensional models of infrastructure, roads certification, GIS, executive survey, the establishment of the longitudinal and transverse profiles, etc.;
  • Power engineering;
  • Creating three-dimensional models and topographical plans CHP, HPP, electrical substations, transmission lines;
  • Architecture and Urban Planning;
  • Creating three-dimensional models and GIS on neighborhoods and monuments;
  • Oil and gas, metallurgy and heavy industry;
  • Creation of three-dimensional models, topographical plans, industry executive surveys, compressor stations, open-cut mining;
  • Monitoring of slope processes (landslides, sedimentary accumulation).

 

Advantages of the technology:

  • Significant cost savings as compared with traditional survey methods.
  • High accuracy and detail of the data with the relative accuracy of 8 mm, premier centimeter-level absolute accuracy, and about 3,000 points per 1 sq. m. at 60 km/h detail;
  • Increased safety when surveying at dangerous objects (high power electrical stations, railways objects, chemicals).
  • high efficiency - up to 300 linear kilometers per day;
  • high mobility (the system can be installed on any vehicle).

 

MLS Technology Description

Mobile laser scanning system consists of 2 main parts: the measuring unit and the navigation unit. The measuring unit, similar to the system TLS, scans objects while the positioning system provides the scanner trajectory with a "reference" in navigation. Here is a more detailed description of the system available, for that matter, in our company's mobile laser scanner Riegl VMX-250.

The distance-measuring unit consists of 2-pulse laser scanners running as the profiler. During the time delays, each scanner measures the distance to an object with a frequency of up to 300,000 Hz, at a distance of up to 500 m. Thus, the overall frequency of the system is up to 600,000 measurements per second. Rotating at 100 Hz, the deviation prism produces a scanning beam in a full circle (0-360 degrees). Simultaneously with the distance measurement, a registration of the scanning beam deflection angle is performed. The measured distance and angle serve to determine the points’ coordinates in the scanner coordinate system, thereby providing a "Spot Mode” scanning sweep of the cloud of points in the transverse-to-motion direction.  Longitudinal "sweep" is produced by moving the scanning system-carrying vehicle along the scanned object.

Coordinat and time binding of the resulting point cloud is performed by a high-precision positioning system consisting of a GNSS receiver and inertial unit. The GNSS receiver determines the current position coordinates of the scanner unit, usually with a frequency of 1 Hz, as well as the exact time, to synchronize all elements of the system. The inertial system, based on a GNSS receiver, determine its initial position, and then measures the coordinates and orientation angles of the scanner unit at the rate of 200 times per second. The inertial system cannot operate autonomously for a long time because it has a so-called "drift", i.e. coordinate accuracy degeneration with time, so from time to time it has to be adjusted based on the GNSS receiver data. In normal mode, this is one time per second, but, as confirmed by experience, the absence of GNSS data for up to 30 seconds, results in the accuracy deterioration of not more than 1-2 cm. With the system in normal mode (no interference to satellite signals), the standard root-mean-square error of the spatial coordinates is about 2-5 centimeters. The formation of the cloud of points along the scanner trajectory and integration into the desired coordinate system is performed based on a combined post-processing data of all MLS subsystems (rangefinder and trajectory).

The Riegl VMX-250 scanning system is also equipped with 4 calibrated digital cameras mounted on the same platform with the scanner. The cameras perform an automatic mode shooting with the specified frequency (up to 20 frames per second). The use of the cameras allows colorizing of laser reflection points in true colors, which greatly facilitates the interpretation of objects point by point, and can also be used for texturing three-dimensional models.

Types of outputs

The MLS technology is mainly used to create the following types of finished products. In addition, it is quite possible to successfully develop many other MLS data-based types of applications, such as:

  • Determination of dimensions and compilation of geometric rating plates for engineering projects;
  • Report of deformation road surface (rutting, potholes, cracks) and the railway;
  • Longitudinal and transversal profiles of linear structures Digital terrain models, etc.

 

Compilation of DTM (digital terrain model)-based transversal profiles.

Compilation of DTM (digital terrain model)-based transversal profiles.


Places of deformation on road surface

Places of deformation on road surface

Road section with revealed rutting

Выявление колейности на автодорогах

Road section with revealed rutting

Report of deformation road surface

Report of deformation road surface

 

Equipment

The sophisticated Riegl VMX-250 mobile scanning system is used by the "NIPIStroyTEK" company to perform a mobile scanning. This system combines all the advanced developments in laser scanning, navigation measuring and mobile photographic surveying. Riegl VMX-250 allows scanning and performing photographic surveying of the area concerned at high speed, density (600,000 measurements / s, up to 20frames / sec) and accuracy (intrinsic accuracy - 8mm).

Technical details of the Riegl VMX-250 mobile scanning system:

Specification

Value

Number of scanners

2

Scanning Frequency

100 кГЦ – 600 кГц

The frequency of measurement

600,000 measurements /sec (2 x 300,000 measurements /sec)

The maximum measurement range

at 100 kHz - 180 m (reflectivity factor > 10%)
at 100 kHz - 500 m (reflectivity factor > 80%)
at 600 kHz - 75 m (reflectivity factor > 10%)
at 600 kHz - 200 m (reflectivity factor > 80%)

Scanners’ viewing angle

360°

The number of received pulses from one outgoing

Virtually unlimited

Accuracy of measurement

8 mm (at 150 m distance)

Accuracy INS /GNSS
-Absolute
-Relative
Tangage/Swing
Course

Standard 20-50 mm
Standard 8 mm
0.005 °
0.015 °

Number of cameras

4

Camera Sensor Resolution

5 megapixel (2448x2050)

Maximum shooting frequency

20 frames/sec (4 x 5 frames /sec)