R200 parameters

[LdePa]

I've been working with the R200, but nowhere can I find its focal length or sensor size. I've tried doing the calibration with the chessboard pattern but it didn't seem to work. Can anybody help me with that?

[MartyG]

If you are using Windows, the RealSense SDK version '2016 R2' SDK has scripting functions for retrieving color focal length and depth focal length.

Color focal length

https://software.intel.com/sites/landingpage/realsense/camera-sdk/v1.1/documentation/html/index.html?querycolorfocallength_device_pxccapture.html

Depth focal length

https://software.intel.com/sites/landingpage/realsense/camera-sdk/v1.1/documentation/html/index.html?querydepthfocallength_device_pxccapture.html

'2016 R2' is the last version of the old Windows SDK that supports the R200. If you are not currently using this SDK and would like to try it, it can be downloaded directly in the browser as a 1.8 gb file from this link:

http://registrationcenter-download.intel.com/akdlm/irc_nas/vcp/9078/intel_rs_sdk_offline_package_10.0.26.0396.exe

There is also a pre-made Windows camera calibration program for the R200.

https://downloadcenter.intel.com/download/24958/Intel-RealSense-Camera-Calibrator-for-Windows-

[LdePa]

Thanks for the answer,

I can't really do it this way though, my R200 is attached to a drone and therefore I can't connect it to the computer.

Wouldn't you know a way to discover the parameters via wi-fi or some other way?

[MartyG]

With the Intel Aero drone system that uses R200, it is possible to communicate with applications on the drone's onboard computer from a ground computer via wi-fi. Is your drone setup based on Intel Aero, please?

https://github.com/intel-aero/meta-intel-aero/wiki/08-Aero-Network-and-System-Administration

[LdePa]

Yes, it is the Intel Aero. I've already managed to connect my computer with the drone's wi-fi, but I did not manage to get the camera calibration working (am I just stupid?). Also, I just realized from the website you sent me, that the R200 does not support the QueryColorFocalLengthMM, which is the one I need.

[MartyG]

There seems to be very little information regarding calibration of the R200 that comes in the Intel Aero Vision Accessory Kit, if that is the one that you are using. I did find a promising looking university paper on a quadcopter that uses Aero and the R200 though.

https://people.ece.cornell.edu/land/courses/eceprojectsland/STUDENTPROJ/2017to2018/sl2462/project_68_report.pdf

On page 12 they list the calibration values for the R200 that they got through testing. This page says "The parameters, shown below, were found in one of two ways. First a custom written script was written to find the camera’s intrinsic parameters – calculating various fields based on these values – and second, were hand tuned through repeated testing". 

 The research I have done indicates that the calibration information is fixed on the R200 and is read-only. So applications / scripts can output the calibration information but not change it.

[LdePa]

That certainly helps, but as far as I know, the camera.fx and camera.fy are the focal lengths in pixel. I need the focal length in mm, and to find it out, I'd have to divide those fx and fy by some kind of (pixel/mm) variable, since:

and

I know the resolution of the camera is 640x480, but how could that help me find sx and sy?

[MartyG]

Someone else who once had the same problem said that the link below helped them to convert the R200's pixel focal length to mm.

​https://cs.stackexchange.com/questions/86328/how-to-convert-pixel-relative-focal-lengths-to-mm?language=en_US

[LdePa]

Yes, I've found this website before, but it requires the sensor size (x and y) of the camera which is also unknown.

[MartyG · Accepted solution]

Although the manufacturer of the sensors in the original RealSense cameras is not listed in the data sheet, I had a memory that the manufacturer had done a press release about it around the time of RealSense's original launch. Apparently the original generation used an IR sensor by Foundry Tower Semiconductor, and the sensor had a 3.5-micron pixel size.

https://www.eenewseurope.com/news/tower-makes-ir-sensor-intel-realsense

[LdePa]

Hmm, alright. I'll keep that in mind. Thanks for the help!