ALS

Airborne Laser Survey

There are two major modes of data processing

Basic data processing:

Basic data processing is implemented through a set of algorithms used to derive primary laser data. It includes calibration, express analysis, pilotage quality control and some other procedures. All basic data processing algorithms are designed to support data formats employed by power line design and survey companies

Thematic data processing:

Thematic data processing is oriented to address general geodetic and cartographic tasks

Basic Data Processing Capabilities Offered by ALTEXIS Software Package:

Express analysis of survey data
Simultaneous representation of laser scan data (laser points) in plane and profile
Separation and color-coded presentation of data relating to various legs of the flight. Color coding (deletion from the screen) of laser points relating to individual passes
Direct access to any leg of the flight in the flight path window
Overlaying of the digital map with the flight data in the flight path window
Image zoom function available in flight path, plane and profile view windows (images can be visualized at any selected scale); image rotation function available in plane and profile view windows (plane and frontal rotation)
Data visualization by way of a parallel projection with the deletion of invisible points
Color-coding of laser points according to their geodetic altitude. Color-coding parameters can be set up automatically or manually;
Indication of geodetic coordinates (North, East, Altitude) of any laser point and current cursor position
Creation of spatial corridors to select data for plane and profile views (Select Corridor)
Plane and measurements
Manual setup of vector objects of vertex, polyline or polygon types with relevant parameters
Visualization of geo-referenced digital aerial photos with respect to the scale and location of laser data
Plane measurements using aerial photos
Selection of a system to represent current coordinates
Algorithm allowing the identification of true ground surface points and automated layer-by-Iayer differentiation of data relating to various objects, including power transmission lines. Visualization of individual layers with the parameter setup function
Representation of ground surface points as a group of lines of equal altitudes;
Semi-automated technique of locating power line towers as models of a particular type
Ability to incorporate and edit parameters of power lines, towers, conductors
Geometric measurements, determination of sags and power line clearances. Automatic creation of the reference data sheet
Easy export of data and aerial photos into CAD and GIS systems.

Processing of laser scan data obtained from the survey of an overhead power transmission line includes morphological differentiation of primary laser points. The first stage is separation of laser points by the criterion "ground or ground object". Then the whole collection of the points composing the laser scan image is separated according to classes of the objects using comprehensive algorithms of geomorphologic analysis.

There are the following classes:

Conductors;
Towers;
Insulator strings;
Guys;
Ground (true terrain features)
Vegetation
Buildings and structures; Fences

The morphological differentiation of laser points is followed by the next stage of data processing, i.e. by the creation of meaningful vector models of overhead power transmission lines. A vector model of any object is mathematically completely formalized, so this object can be exactly located in space. Besides, the representation of an object as a model allows the assignment of certain semantic parameters whose values can be determined by way of modeling. If an operator attributes a number of mechanical properties to the conductor model, then the following parameters can be calculated:

length of the conductor in plan
overall length of the conductor
sag
stress
ground clearance
distance to vegetation

The resultant representation of the scene contains both primary laser scan data and vector images of geographical objects, thus allowing the automated determination of clearances as well as the manual measurement of geometric parameters.

Aerial laser surveys are conducted with the intensity of reflected pulses measured in more than 5000 distinguishable shades. This makes it possible to produce completely geo-referenced orthogonal images of almost the quality of black-and-white aerial photos. These images can be used as an additional source of information (along with digital aerial photos) for the purpose of interpretation and contouring. Besides, such images can be used when aerial surveys are performed at night.