Thermal Compensation and Calibrating

[Jrmay1]

Hello,

I hope this message finds you well. I have a few questions regarding thermal compensation and its interaction with calibration parameters. I would appreciate your insights on the following:

1. Calibration Parameters with Thermal Compensation:
   What is expected of the calibration parameters when thermal compensation is active? Are there any specific considerations or adjustments we should be aware of?

2. Recommended Calibration Conditions:
   What are the recommended temperature conditions when calibrating the cambar? Is there a specific temperature range that ensures optimal calibration accuracy?

3. Temperature Consideration During Calibration Application:
   When a calibration is applied, is the current temperature taken into account? If so, how does this influence the calibration process or results?

Thank you in advance for your support!

Best regards,
JRMay

[MartyG-RealSense]

Hi @Jrmay1 Thanks very much for your questions.

1. One of my RealSense colleagues who is a calibration expert provided the following advice about having thermal compensation active during calibration on camera models that support it before performing calibration with the Tare calibration feature of the RealSense Viewer tool (Tare improves depth measurement accuracy, whilst On-Chip is focused on improving depth quality rather than accuracy):

"While it is recommended to disable thermal compensation on D455 before running Tare, in my experience this is a minor issue and would lead to very small discrepancies under most conditions".

Thermal compensation is a feature on D455-type cameras (D455, D455f, D456, D457). If you have a D405, D415 or D435 type camera (D435, D435i, D435f, D435if) then thermal compensation does not occur.

The official calibration documentation at the link below states that thermal compensation is disabled by default when performing calibration in the RealSense Viewer.

https://dev.realsenseai.com/docs/self-calibration-for-depth-cameras

2. The official recommended maximum internal operating temperature (ASIC temperature) of RealSense 400 Series cameras is 35 degrees C, though you could likely go to around 42 degrees C before depth problems might start manifesting beyond that temperature. So ideally the camera will be below 42 degrees during calibration. A severe temperature event may possibly result in mis-calibration of the sensors.

3. As far as I am aware, the current detected temperature value is not taken into account as a parameter during calibration and the calibration documentation does not refer to it doing so. As mentioned above though, a very high temperature could result in a mis-calibration of the sensors occurring, which can be corrected with the calibration tools.

As an alternative to performing a calibration, you can also reset a camera to its factory-new default calibration values at any time in the RealSense Viewer using instructions at #10182 (comment)

[Jrmay1]

Hi Marty,

Thank you for your response.

When calibrating, I ensure that thermal compensation is disabled. However, my concern lies in understanding how thermal compensation utilizes the calibration data.

For instance, if I calibrate my lens at 15°C, will the thermal compensation process account for this differently compared to calibrating the lens at 20°C? Additionally, is there an optimal temperature at which I should perform the calibration to ensure the thermal compensation functions most effectively?

Taking this further, after the calibration, if I read the calibration when its 15 degrees, compared to 20 degrees, shoudl I expect the calibration information to have changed? If so, what changes should I expect?

Thank you again

[MartyG-RealSense]

There is very little publicly available information about how the thermal compensation mechanism operates, unfortunately. Sometimes a lack of public information about an algorithm may be because it is commercially sensitive proprietary info that needs to be kept confidential to RealSense.

In general though, as long as the camera's internal temperature is above 0 degrees C and below 35 degrees C (the official recommended min-max operating temperature range) then there should be no need to take the current camera temperature into consideration during calibration.

[Jrmay1]

Hi Marty,

Thank you for your advice!

[Jrmay1]

Hi Marty,

Just to clarify, you mention that we can run the calibration process at any temperature between 0 and 35, without taking the temperature into account. If the temperature has so little affect on the calibration, why is the thermal compensation algorithm present at all?

Or is it that the realsense camera does record the temperature when the calibration is applied, and so the thermal compensation can use this calibration/temperature combination as a reference?

[MartyG-RealSense]

Thermal compensation is helpful when using the camera in environments where there are significant shifts in temperature at different times of the day that could cause a noticeable variation in measurements. This is discussed at #8434 in a case involving a camera model not equipped with compensation where depth varied by 15 mm over a 12 hour period as the room temperature changed from 25 to 35 degrees C.

An increase in environmental temperature that heats the outer casing of the camera can also cause the internal ASIC operating temperature to rise.

When using camera calibration tools however, temperature is not a factor that you need to take into account so long as the camera is not severely hotter than the recommended maximum (i.e hot enough to cause a sensor mis-calibration due to micro-distortions).