The ground 3D laser scanning system is mainly composed of 3D laser scanner, computer control unit, power supply system, bracket and system supporting software. System, internal drive device, CCD camera, control system and other auxiliary function systems.
When the 3D laser scanning instrument is working, the laser ranging system emits laser light to the object to be measured, and the timing system records the time from the launch to the return of the laser, while the angle measuring system captures the horizontal and vertical angles between the scanning instrument and the object to be measured. , through the system-integrated drive motor and laser steering mirror, the scanning area is covered by scanning, so as to realize the three-dimensional coordinate acquisition of the measured object.
While acquiring the three-dimensional coordinate information of the target object, the laser reflection intensity (Intensity) of each point will be recorded synchronously, and the RGB color information of each point of the target object will be acquired by the CCD camera. Therefore, the obtained point cloud data is no longer the three-dimensional coordinate data obtained by the traditional total station, but more abundant data including reflection intensity and RGB color digital information.
During the measurement process of the 3D laser scanning instrument, the coordinate system defined by itself is used as the benchmark. The laser emission point, that is, the intersection of the horizontal and vertical rotation axes, is the coordinate origin. The Z axis is located vertically upward in the vertical scanning plane, and the upward direction is Positive; the X-axis and the Y-axis are perpendicular to each other in the plane, the Y-axis points to the object in the positive direction, and together with the X-axis and the Z-axis constitute a right-hand coordinate system. As shown below.
The three-dimensional laser scanning instrument does not directly obtain the coordinates of the measured object, but obtains the three-dimensional coordinates of the measured object through the inverse calculation of the distance measured by the laser and the horizontal and vertical angles. Does the data measured by the instrument have the time from laser emission to return? ? ? , distance S, vertical angle? ? with the horizontal angle? ? , the three-dimensional coordinates of the point can be calculated by the following formula:
where C is the speed of light, ? ? ? is the round-trip time of the laser. The main technology of the 3D laser scanner The laser ranging technology can be divided into three types in terms of ranging principle: the pulse ranging method based on the pulse round-trip time to measure the distance, the laser triangulation method and the phase ranging method using the phase measurement principle. The laser triangulation method is used to solve the triangle calculation distance by turning the spot imaging position into a “corner and corner problem”.
The phase ranging method uses uninterrupted integer wavelengths, and indirectly calculates the distance of the measured object by recording the phase difference generated by the round-trip propagation of the signal. The distance S can be obtained from the following formula.
where c is the speed of light, ? is the phase difference, ? ? is the part of the round-trip phase difference of the signal less than 2??, f is the pulse frequency, n is the half-wavelength integer of the modulating signal, ? ? ? is the fractional part of the insufficient wavelength.