Laser radar base: coordinate system (translation)
We are familiar with the processing laser radar coordinate system mounted on the autonomous vehicle of the point cloud data. In this article, we will examine the coordinate system LIDARS used.
To calculate the exact distance of the object we are concerned with the photometric and ranging using a laser radar.
The distance to the object is calculated using the time of flight of the laser radar.
When the laser pulse emission, and the emission direction of the time will be recorded. Laser pulses propagating in the air, until it encounters an obstacle which reflects some of the energy. After receiving the portion of the energy, received by the sensor and the acquisition time of recording. Spherical coordinate obstacle by a sensor and the return time after each scan the received power (the reflectance) is calculated.
Since the laser radar sensor is a special spherical coordinate system value, let's review the special spherical coordinate system.
Spherical coordinate system
In the spherical coordinate system, the point defined by the distance and two angles. In order to express these two angles, we use the azimuth angle (Th) and polar angle (gamma]) convention. Thus, by point (r, τ, γ) defined.
As can be seen from the above diagram, the azimuth measuring the XY plane in the X-axis, the polar angle is the ZY plane Z-axis measurement.
From the above chart, we can get the following equation to convert the Cartesian coordinates to spherical coordinates.
You can use the following equation is derived from the ball Cartesian coordinates.
Laser radar coordinate system
Laser radar returns spherical coordinate readings. As can be seen from the following chart, discussed above practice is a little different.
In the sensor coordinate system, the point (radius R, [omega] elevation, azimuth [alpha]) defines a point. Elevation angle, ω is the ZY plane as measured from the y-axis. XY plane azimuth angle α measured in the y-axis.
Depending on the azimuthal position of the laser emission, and recorded at the time of emission. A laser emitter fixed to the sensor elevation. Radius is calculated using the time of the return beam.
Cartesian coordinates can be derived from the following equation.
Cartesian coordinate system is easy to operate, so we need to use the above equation to convert the spherical coordinates into Cartesian coordinate system.
Therefore, the sensor data from the spherical to Cartesian coordinates using the above equation. Drivers laser radar sensor is typically done for us. For example, Velodyne LiDARs sensors ROS package. Vero Virginia point cloud for transforming the coordinate system.
One kind of car equipped with laser radar coordinate system.
The figure shows a Cartesian coordinate system of a sensor mounted on an automobile.
Thus, in this article, we learned how to calculate the distance and the laser radar coordinate system.
Translated from: https://hackernoon.com/lidar-basics-the-coordinate-system-a26529615df9
