Data format for Las

In essence, the LAS format is a binary file format. The goal is to provide an open format standard that allows different hardware and software providers to output a unified, interoperable format. Now the LAS format file has become the industry standard format for LIDAR data.

The LAS files hold data in each scan line arrangement, including three-dimensional coordinates of the laser point, multiple echo information, intensity information, scanning angle, classification information, flight information, flight posture information, project information, GPS information, data point color information and so on. The data types used in the Las format definition follow the C language standard of 1999 ANSI (Americannationalstandardsinstitute, National Standardization Association of America).

A lidar file that complies with the LAS Standard is divided into three parts: a common file header block (publicheaderblock), a variable length (variablelengthrecords), and a point data record (Pointdatarecord).

C--class (owning Class)
F One flight (route number)
T one time (GPS)
I one intensity (echo strength)
R One return (first return)
n A number of return (echoes)
A a scan angle (scanning angle)
RGB One red green blue (RGB color value)

Filtering: Removes data points that are not useful for generating a digital elevation model (DEM), including error points and feature points.
Filter principle: Based on the abrupt change of elevation, that is, when the elevation changes between the adjacent two laser points are large, it is generally thought that it is not caused by the abrupt fluctuation of the terrain, more likely due to the presence of ground objects, the higher elevation point is probably not the ground point. If the distance between two points is closer, the higher the difference, the higher the point is more likely to be a figure point, so judge whether a point is the ground point, to consider the point to the reference ground point distance, with the increase of distance between two points, its high difference will also become larger.

Data format for Las