Working Distance and Camera Positioning
In this tutorial, we will learn how to position the camera correctly. We will cover different considerations such as FOV, working distance, and image blooming.
In many applications the camera will be stationary mounted to capture point clouds with a constant FOV. In other applications, the camera may be mounted on the robot arm, which yields a lot more flexibility on how the camera can be positioned to capture good point clouds. In both alternatives, the camera needs to be positioned such that it is optically optimized for a given scene.
When finding the correct working distance, there are a few things to take into consideration:
What is the area or volume that the camera needs to see?
What is the size of the objects that the camera needs to see?
What is the required spatial resolution and precision in the working area or volume?
Once we know the answers to these questions, we can check if the Zivid camera satisfies the requirements by the means of:
Manual validation by capturing and inspecting a point cloud using Zivid Studio.
Information about Zivid camera point precision and spatial resolution as functions of the working distance can be found in the datasheet and the FOV and imaging distance calculator.
Be aware that the noise is proportional to the working distance, and that the spatial resolution is inversely proportional to the working distance.
We may proceed if all requirements for working distance, FOV, resolution and precision can be satisfied with a single camera position. If not, we need to consider using robot mounting, multiple cameras and so on. In that case, we recommend that you contact firstname.lastname@example.org and we will help you find a solution.
The imaging sensor inside Zivid cameras is offset at a slight pan angle in the azimuth direction (y-axis). This should be considered if it is desired to have the camera perpendicular to the scene.
The 2D camera and the projector have an angle with respect to the center axis.
This should be considered if it is desired to have the camera perpendicular to the scene.
Although it is perhaps most intuitive to mount the camera perpendicular to a scene, this is usually not the best way. If possible, mount the camera at a slight tilt angle to avoid reflections from the background, as explained in Blooming - Bright Spots in the Point Cloud. This also frees up space above the scene for easier access for tools and robots. Check out available Zivid mounts.
Camera tilting is more important if the scene contains specular surfaces.
An exception is if you are imaging large parts that are extremely specular, and in particular, also dark. Here you may benefit from mounting the camera perpendicular to the part to maximize the signal back to the camera.
For bin-picking applications, place the Zivid camera projector above the back edge or above the rear corner of the bin (see images below). Pan and tilt it so that the 2D camera is looking at the center of the bin. The projector rays should not fall on the inner surfaces of the two walls closest to the projector; they should almost be parallel to those two walls. Mounting the camera this way minimizes interreflections from the bin walls.
In general, it is always recommended to put the camera as close to the scene as possible. This is because the accuracy is better at shorter imaging distances. However, accuracy is best in the center of the image and decreases towards the corners (see the image below).
Therefore, we recommend installing the camera at a distance slightly larger than the minimum to avoid using 5% of the image from its edges. For most applications, this will happen naturally due to the mounting safety margins.
Zivid cameras are very robust against defocus, but to maximize the precision of the point cloud, the depth of focus should be taken into consideration. This step is only required if the algorithm that will work on the point cloud requires it in order to be successful.
A lower degree of focus will degrade precision and enhance the Contrast Distortion.
Find the upper recommended aperture (lower recommended f-number) that we should use for the given working distance by looking at the table from Depth of Focus section. Alternatively use the Depth of Focus Calculator by selecting the camera model and inputting the closest and farthest working distance. It is recommended to set “Acceptable blur radius (pixels)” to 2.
When we have found our working distance, it is time to find the right camera settings. We will cover this in Getting the Right Exposure for Good Point Clouds.