Revision 1.1
Intel RealSense™ cameras leave the factory meeting all datasheet specifications. Due to shipping, handling, or adverse environments the quality of depth accuracy may be impacted. The purpose of this document is be a Reference Guide for Intel® RealSense™ Stereo Depth Cameras to ensure the positive Out of the Box (OOB) experience and keep the optimal performance over the lifetime. This document references other documents but will cover key steps in its guidance.
It is not in the scope of this document to discuss the details of depth or calibration deeply. Additionally, modules are out of scope of this documentation but described to ensure it is clear what is out of scope.
This document contains five main parts: definitions, tools, incoming, integration and outgoing considerations:
Table 2-1. Terminology List
(Optical Head)
(DQT)
Table 2-2. Integration Process Tools List
Table 2-3. Integration Considerations
Note: All information (such as mounting and routing) for these considerations are in the https://dev.intelrealsense.com/docs/intel-realsense-d400-series-product-family-datasheet.
Intel® RealSense™ Cameras D400 series camera is a plug-and-play USB3.1 high quality stereo depth camera. USB 2.0 is supported also. Just simply follow the mounting guidelines in the datasheet and gain access to the SDK and depth streaming will be enabled. Intel® RealSense™ SDK 2.0 is a cross-platform library for Intel® RealSense™ depth cameras. It is an open source SDK and can be accessed at https://www.intelrealsense.com/sdk-2/.
Figure 2-1. Camera USB Connection
Figure 2-2. RealSense Viewer Depth and RGB Images
Figure 2-3. RealSense Viewer On-Chip Calibration
Figure 2-4. Health-Check Number
If you see the Health-Check and FL-Health-Check numbers are all “Good”, you are ready to go!
All RealSense camera sensor modules are built from factory to be extremely sturdy, encased in laser-fused steel cages, with the intent of maintaining calibration and performance over their lifetime. However, conditions can occur that lead to degradation over time, such as exposure to extreme temperature cycling, or excessive shock and vibe. Whatever the cause, Intel provides a set of tools to recalibrate cameras back to their pristine factory condition and keep the best performance over lifetime. These tools include “Self-Calibration”, “Dynamic Calibration, and “OEM calibration”.
To keep Intel® RealSense™ Cameras optimal performance, Intel® RealSense™ offers three types of calibration, namely, Self Calibrtion, Dynamic Calibration, and OEM Calibration. For module integration and factory environments, Intel strongly recommends the purchase of an OEM calibration target and learning the accompanying tools. Please work with the Intel Sales and Support teams to gain access. Table 3-1 are the considerations when selecting a calibration type.
Table 3-1. Calibration Types
Self-Calibration is the the most convenient and easiest calibration for users. It can be used when you open the box – incoming quality validation. Or after the cameras are mounted on your devices in the field. The calibration is running inside the VPU chip inside the camera. It calibrates only depth camera.
Dynamic calibration can be executed either in lab or in the field. It requires a A4 printed paper target or a smart phone target. It calibrates both depth and RGB cameras.
OEM calibration is the most robust calibration method for Intel® RealSense™ stereo cameras. It requires a big V shape calibration target. It is used in the factory setup or in the lab. It is highly recommended if you purchase RealSense cameras modules and ASIC cards and build the camera enclosure yourselves. It will rectify all kinds of distorations introduced by mounting the modules into the new enclosures.
Self-Calibration includes two parts, namely On-Chip Calibration and Tare Calibration.
On-Chip Calibration is to minimize the noise. Tare Calibration is to improve the depth accuracy.
Figure 3-1. RealSense Viewer On-Chip Calibration
After you run On-Chip Calibration you will get “Health-Check” number.
Figure 3-2. Health-Check Number
Table 3-2. Health Score Meaning
Table 3-3. On-Chip Calibration Health Check Results Next Steps
Note1: On-Chip Calibration works best when the camera is pointed at scenes with details. Note2: These numbers are guidelines and not absolutes. It is important for each camera to be validated as an acceptable depth map for the desired usage as depth map requirements vary based on usage.
Figure 3-3. RealSense Viewer Tare Calibration
Figure 3-4. Tare Calibration Ground Truth
When you run the Tare Calibration, you will need to provide the ground truth. A laser range finder is a good tool to provide a good ground truth.
Dynamic Calibration is a good calibration option if Self-Calibration does not resolve camera quality issues. The Dynamic Calibration Tool can be found at same site as the quick start guide: https://dev.intelrealsense.com/docs/d400-dynamic-calibration-quick-start-guide. It is one of the tools to the left of the page. Due the extensive capabilities of Dynamic Calibration a target is suggested. There is a target-less solution, but Intel suggests a target be used. This document will assume a target is used. While the tool offers an excellent step by step demo the steps for dynamic calibration are:
Figure 3-5. Dynamic Calibration Target
Figure 3-6. Dynamic Calibration
With Dynamic Calibration the camera must be aligned with the target initially and then moved to multiple locations. This must be done with depth and RGB calibration. Please follow the User Guide and application. The result should be a successful calibration as shown in Figure 3-7.
Figure 3-7. Dynamic Calibration Successful
Locate the “OEM Calibration Tool” app icon on desktop. This application is available once you buy the target from Intel. The target is located at: https://store.intelrealsense.com/buy-intel-realsense-d400-cameras-calibration-target.html. Intel does not share the software without the target to ensure there is no confusion in the calibration process.
Figure 3-8. OEM Calibration Icon
Double click to launch the tool. All connected Intel® RealSense™ Camera D400 series Depth Camera devices will be listed in the drop-down combo box. The list is presented with each device’s serial number. If all devices are not listed, use the refresh button to refresh the list.
Choose the desired device to be calibrated from the list. Details of this device include its serial number, SKU and Firmware version. This ensures the right device is selected in case multiple cameras are connected to your host system.
Figure 3-9. OEM Calibration RealSense™ Device Details
Once the correct device is selected, click the “Start Calibration” button to start the calibration process. A window with live streaming appears. The SKU, FW version and serial number of the device is displayed in the top left and right corners of the Window. Wait a few seconds for the device to warm up and get ready for calibration.
Figure 3-10. OEM Calibration Process Start
Once the camera finishes warming up, a capture button appears on the right side of the Windows*. In the next steps, user will need to move the device to the two pre-defined locations and use this button to capture images for calibration.
Images from two viewpoints from pre-defined positions are required for the OEM calibration algorithm.
Table 3-4. OEM Calibration Position Details
Figure 3-11. Pre-defined Positions
Figure 3-12. Marked Position Viewpoint #1 (Close Position #1)
Press the capture button at the right side to capture the image for this position. The software verifies the image and either accepts or rejects it. If it’s accepted, it will display a green progress bar at bottom and the status message will be changed to “1/2 Valid Images”. If it’s rejected, then no progress will be made, and a red error message will appear on screen and instruct user to recapture image at this position.
Once the image for position #1 is successfully captured, move the camera to position #2.
Figure 3-13. Marked Position Viewpoint #2 (Far Position #2)
Repeat the process from Position #1
Once the images from the two viewpoints are captured, the OEM Calibration Tool will automatically start compute of the calibration algorithms can usually takes 30 seconds.
Figure 3-14. Calibration Algorithm Run Window & Update
A message box will appear to indicate a calibration pass or fail.
Figure 3-15. OEM Calibration Success or Fail
If the calibration fails during any of these steps, it will display an error message box. In that case, user will need to execute this process again. Intel suggests on executing OEM calibration up to three times. If failure continues then we suggest working with Intel support teams. If the camera passes OEM calibration, Intel suggest that DQT is executed again to ensure that the Intel camera is functioning properly. If the camera passes DQT then it is ready to use. If not then contact your support team at: https://www.intelrealsense.com/support/. If you are an NDA customer, please use your Zendesk account.
This application allows you to test the camera’s depth quality, including: Z-Accuracy, Sub-Pixel and Z RMS errors (spatial noise) and Fill Rate. You should be able to easily get and interpret several of the depth quality metrics, or record and save the data for offline analysis.
Once the RealSense™ SDK is installed The Depth Quality Tool (DQT) is also installed. Launch the DQT (icon below).
The Depth Quality Tool measures the cameras depth accuracy as reported in the z plane to match geometric location markers of x (horizontal), y (vertical) and z (depth). The tool requires an accurately known distance (ground truth) to be entered by the user to ensure the z-accuracy is correct. The more accurate the ground truth the more trustworthy the results of z-accuracy are in the depth quality. Do not underestimate the difficulty of imputing a good ground truth. A laser range finder is a good method. Intel also suggests that ground truth is near the specification of the camera. For example, z-accuracy specification D435 is 2% accuracy at 2 meters. This means a distance exactly 2 meters away would measure between 1.96 meters and 2.04 meters on a camera that is functioning properly. Most RealSense™ Depth Cameras commit to 2% accuracy at 2 meters. The newly released D455 commits to 2% accuracy at 4 meters. The fill rate should be equal or greter thn 99%. The RMS error should be equal or less than 2%.The temporal noise should be equal or less than 1%.
The DQT will give clear placement instructions to yield the most accurate results. If the accuracy is less than the committed specification for your camera then it is ready to use. If the accuracy is greater than the specification, for example on D435 it is 4.8% at 2 meters then go to section Dynamic Calibration3.5.
Figure 3-16. Depth Quality Tool
Figure 3-17. Depth Quality Tool Flow
Note: This is the complete flow for DQT, but if Self-Calibration has already been run then move to step 2b
Historically, Intel® RealSense™ Cameras quote the accuracy to be less than 2% error at 2 meters. The D455 specification is 2% at 4m. As stated earlier, the DQT is best when the measurement distance is very close to the specification range of the cameras.
Intel® RealSense™ Depth Camera products are robust and ready to use as a great solution for many compute visions challenges. Additionally, while this document has details on calibration techniques and product specs it is not comprehensive. Please ensure to reference the documents mentioned in the tools section of this document as well as the wealth of information on https://www.intelrealsense.com/.
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