In machine vision scenarios, the calibration between the camera and the robot affects the accuracy of the data. Therefore, selecting the correct camera coordinates is crucial. This article provides a detailed explanation of how to select the coordinates for the Vzense 3D ToF(Time of Flight) camera.
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What is the origin of the camera coordinates?
The origin of the camera coordinate system is the center of the camera’s lens. The x-axis and y-axis are parallel to the X and Y axes of the image, while the z-axis represents the camera’s optical axis, which is perpendicular to the image plane. In practical applications, by properly positioning the camera based on the origin of its coordinate system, users can capture more image data within the camera’s field of view. This facilitates tasks such as robotic arm gripping and other operations.
The origin of the Vzense 3D ToF camera coordinates
The Vzense 3D ToF camera includes RGB camera and ToF camera, as shown in the image below:
Each camera has its own coordinate system, namely the ToF coordinate system and the RGB coordinate system. Users can select either coordinate system as the camera coordinate system based on their needs.
1. If the ToF coordinate system is used as the camera coordinate system, the origin of the coordinate system is as shown in the image below:
The origin of the X-axis is located 25mm from the bottom edge of the product;
The origin of the Y-axis is located 52.3mm from the left edge of the product;
The origin of the Z-axis is located on the front surface of the lens.
2. If the RGB coordinate system is used as the camera coordinate system, the origin of the coordinate system is as shown in the image below:
The origin of the X-axis is located 25mm from the bottom edge of the product;
The origin of the Y-axis is located 21.55mm from the left edge of the product;
The origin of the Z-axis is located on the front surface of the lens.
What is the principal point(Cx, Cy) coordinates of the camera?
The principal point coordinates of the camera refer to the center of the image sensor.
How to obtain the principal point coordinates of the Vzense 3D ToF camera?
Before the camera leaves the factory, calibration settings need to be performed. This process writes the camera’s intrinsic parameters information into its system. Users can access the current intrinsic parameters information of the camera through the API to obtain the principal point coordinates.
ScStatus scGetSensorIntrinsicParameters(ScDeviceHandle device, ScSensorType sensorType, ScSensorIntrinsicParameters* pSensorIntrinsicParameters);
typedef struct
{
double fx; //!< Focal length x (pixel).
double fy; //!< Focal length y (pixel).
double cx; //!< Principal point x (pixel).
double cy; //!< Principal point y (pixel).
double k1; //!< Radial distortion coefficient, 1st-order.
double k2; //!< Radial distortion coefficient, 2nd-order.
double p1; //!< Tangential distortion coefficient.
double p2; //!< Tangential distortion coefficient.
double k3; //!< Radial distortion coefficient, 3rd-order.
double k4; //!< Radial distortion coefficient, 4st-order.
double k5; //!< Radial distortion coefficient, 5nd-order.
double k6; //!< Radial distortion coefficient, 6rd-order.
} ScSensorIntrinsicParameters;Sample code:
\BaseSDK\Windows\Samples\Base\DS87\DeviceParamSetGet.
1. If the ToF coordinate system is used as the camera coordinate system, the principal point coordinates from the ToF camera’s intrinsic parameters need to be used. The API is as follows:
ScSensorIntrinsicParameters cameraParameters;
status = scGetSensorIntrinsicParameters(deviceHandle, SC_TOF_SENSOR, &cameraParameters);2. If the RGB coordinate system is used as the camera coordinate system, the principal point coordinates from the ToF camera’s intrinsic parameters need to be used. The API is as follows:
ScSensorIntrinsicParameters cameraParameters;
status = scGetSensorIntrinsicParameters(deviceHandle, SC_COLOR_SENSOR, &cameraParameters);How to obtain the 3D data of a target in the camera coordinate system (i.e., point cloud transformation)?
Point cloud transformation involves converting each pixel in the depth image into a point in 3D space. This process requires the use of the camera’s principal point (Cx, Cy) and depth values. Therefore, selecting the correct camera coordinate system and principal point based on the target image type is crucial for acquiring 3D data within the camera coordinate system.
