Key Parameters and Structure of a Laser Scanning Point Cloud
A laser scanning point cloud is a collection of points in three-dimensional space obtained using a laser scanner. The main parameters of a point cloud include:
Number of Points: This is the total number of points collected by the scanner. It can vary depending on the device, scanning settings, and the size of the object.
Accuracy: This refers to how precisely the scanner measures distances to objects. Accuracy is usually measured in millimeters and depends on the type of scanner and scanning settings.
Density: This is the number of points per unit area or volume. Higher density results in more detailed data.
Resolution: This is the minimum size of an object that can be discerned based on the scanning data. Resolution typically depends on the accuracy and density of the data.
Color: Many scanners can also collect color information, which is stored as RGB values for each point.
Format: This is the file format in which the data is stored. Some of the most common formats include E57, LAS, XYZ, OBJ, PTS, PTX, PLY, and others.
Presence of Normals: These are vectors that indicate the direction perpendicular to the surface at each point in the point cloud. Normals provide important information about the geometry of the object's surface.
Presence of Intensity Values: Some laser scanners can measure the intensity of the reflected laser signal.
Structure of a Point Cloud File
Examining the structure of a point cloud file, it is a digital file where the information is represented in a numerical format. Simply put, if you open a typical point cloud file in a text editor, you will see numerous lines of numerical values, with each line representing information about a point in space. Each line usually contains the following information:
Coordinates of Points: Each point in the point cloud has three-dimensional coordinates (x, y, z), determining its position in space. These coordinates can be expressed in a global coordinate system or relative to some base point.
Intensity of Points: The intensity of points represents a measure of the reflected light and can be used to obtain additional information about the object's surface.
Color of Points (if available): In some cases, laser scanners can also collect color information by overlaying color photographs onto the point cloud. In this case, each point can have RGB values (red, green, blue) that define the color of the point.
Normals: These are vectors that indicate the direction perpendicular to the surface at each point in the point cloud. Normals provide important information about the geometry of the object's surface.
Additional Attributes (if available)
In some file formats, such as LAS or LAZ, additional attributes can be defined for each point. These attributes may include point classification (assigning points to specific classes, such as ground, buildings, trees), timestamps, measurement quality, and others.
General Structure of a Point Cloud File
The general structure of a point cloud file includes records or data blocks that store information about each scanned point. File formats such as LAS, LAZ, PLY, OBJ, E57, and others represent different ways of storing and organizing point cloud data.
It is important to note that each point cloud file format can have its own specific features and structure. Therefore, when working with a particular format, it is recommended to refer to the documentation of the format or the software to obtain more detailed information about the structure of the point cloud file.