Camera-Calibration | Camera calibration based on opencv including basic theory | Camera library

Your misconception is about "focal length". It's an overloaded term.

• "focal length" (unit mm) in the optical part: it describes the distance between the lens plane and image/sensor plane
• "focal length" (unit pixels) in the camera matrix: it describes a scale factor for mapping the real world to a picture of a certain resolution

1750 may very well be correct, if you have a high resolution picture (Full HD or something).

The calculation goes:

f [pixels] = (focal length [mm]) / (pixel pitch [µm / pixel])

(take care of the units and prefixes, 1 mm = 1000 µm)

Example: a Pixel 4a phone, which has 1.40 µm pixel pitch and 4.38 mm focal length, has f = ~3128.57 (= fx = fy).

Another example: A Pixel 4a has a diagonal Field of View of approximately 77.7 degrees, and a resolution of 4032 x 3024 pixels, so that's 5040 pixels diagonally. You can calculate:

f = (5040 / 2) / tan(~77.7° / 2)

f = ~3128.6 [pixels]

And that calculation you can apply to arbitrary cameras for which you know the field of view and picture size. Use horizontal FoV and horizontal resolution if the diagonal resolution is ambiguous. That can happen if the sensor isn't 16:9 but the video you take from it is cropped to 16:9... assuming the crop only crops vertically, and leaves the horizontal alone.

Why don't you need the size of the chessboard squares in this code? Because it only calibrates the intrinsic parameters (camera matrix and distortion coefficients). Those don't depend on the distance to the board or any other object in the scene.

If you were to calibrate extrinsic parameters, i.e. the distance of cameras in a stereo setup, then you would need to give the size of the squares.

You're getting this error because Melodic is the ros distro for Ubuntu 18.04. As of present the most recent release is Noetic which targets 20.04. The version of Ubuntu you're using does not currently have a supported ROS release, as such your only real option is to downgrade if you want ROS.

This is the solution for the first part related to
cameraCalibration()
Never mind, I think I found it. There is an issue with the arguments I provided for the function calibrateCamera()

Now there is a new problem on 21/feb/2021 under EDIT.

Solution for EDIT, problem part 2

The code has errors and there was a slight conceptual problem. image_points_R was never filled and all was appended to image_points_L. The conceptual problem was that 4 times 3D coordinates need not be appended since both L and R cams for a single time frame correspond to the same coordinates.

commented lines 60 and 69, corrected lines 61 and 70

The reason why you cannot print the intrinsics is probably because you got nil in the optional chaining. You should have a look at Apple's remark here and here.

Camera calibration data is present only if you specified the isCameraCalibrationDataDeliveryEnabled and isDualCameraDualPhotoDeliveryEnabled settings when requesting capture. For camera calibration data in a capture that includes depth data, see the AVDepthData cameraCalibrationData property.

To request capture of depth data alongside a photo (on supported devices), set the isDepthDataDeliveryEnabled property of your photo settings object to true when requesting photo capture. If you did not request depth data delivery, this property's value is nil.

So if you want to get the intrinsicMatrix and extrinsicMatrix of the TrueDepth camera, you should use builtInTrueDepthCamera as the input device, set the isDepthDataDeliveryEnabled of the pipeline's photo output to true, and set isDepthDataDeliveryEnabled to true when you capture the photo. Then you can access the intrinsic matrices in photoOutput(_: didFinishProcessingPhoto: error:) call back by accessing the depthData.cameraCalibrationData attribute of photo argument.

Here's a code sample for setting up such a pipeline.