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Why point cloud bent?

Masahiro Suzuka
Prodigy 240 points

This question related with this post : e2e.ti.com/.../506632

When I use OPT8241-CDKEVM with TintinCDKCameraLongRange.conf a point cloud seems bent.

Attached file shows point cloud when OPT8241-CDK-EVM measure flat plane, a point cloud seems bend like semi circle shape.

From my understands it cause from lens distortion. But TintinCDKCameraLongRange.conf includes OpenCV lens distortion correction parameter.

Could you tell me why point cloud bent?

I know that I can get good point cloud if I use calibrated configuration. but I want to know more bit detail.

  • 0
    TI__Intellectual 1680 points

    Hi

    If you see the bottom left corner of the image, you can notice the warning(highlighted in red) saying calibration invalid. This indicates that either a non calibrated profile is used or a parameter is changed which affects calibration. In your case, you have used TintinCDKCameraLongRange.conf which is not calibrated. Kindly use  the calibrated profile TintinCDKCameraMetrilusLongRange.conf and this problem will disappear.

    Point cloud is bent because of common phase offset which you can calibrate with the help of voxel viewer

    Thanks and regards

    Nithin

  • 0 in reply to Nithin Jose
    Prodigy 240 points

    Thanks for reply

    I tried common phase offset calibration with VoxelViewer. but point cloud seems still bent.

    From my understand : "common phase offset calibration" will fix offset of common to all of the pixels.

    so common phase offset calibration will not change point cloud shape. it makes point cloud move to parallel.

    I think I must try pixelwise phase calibration to fix point cloud shape.

    Is my understand correct?

  • 0 in reply to Masahiro Suzuka
    TI__Expert 3800 points

    Suzuka san,

    It is true that changing the constant phase offset will change the offset of each of the pixels to the same value. However, you can observe that between the 2 images you have shown us, the second image with corrected phase offset has better flatness. This happens because phase offset corrects the radial distance in spherical coordinates. A flat wall has different values for 'r' at each pixel. So when you introduce a constant offset in the radial distance, it can look curved.
    Speaking of this in more mathematical terms, a flat wall is not defined by a set of linear equations in spherical coordinates. So changing a given parameter might affect the shape in a "curved" manner instead of having a simple linear translation effect.

    Assuming the camera is showing the distance at the center accurately, you should now be able to correct the remaining bending in the flat wall shape by doing pixelwise phase correction.

    Please let me know if you have further questions.

    Regards,
    Subhash

  • 0 in reply to Subhash Chandra Sadhu
    Prodigy 240 points

    Subhash-san,

    Sorry for late reply and thanks for point out my misunderstand. For reference, Could you tell me what VoxelViewer doing in pixelwise phase correction?

    Best Regards,

    Suzuka

  • 0 in reply to Masahiro Suzuka
    TI__Intellectual 1680 points

    Suzuka-san,

    pixel wise phase correction corrects for the random variations in phase between each pixels. Pixel wise calibration technique employed in the Voxel viewer assumes that the scene is facing a flat wall and corrects each pixel such that it indeed becomes a flat wall. Pixel wise offsets for each pixel is stored in a binary file along with the calibration data.

    Regards,

    Nithin

  • 0 in reply to Nithin Jose
    Prodigy 240 points
    Nithin-san,

    I have one more question.
    Why "remaining bending" occurs? Lens distortion? ADC?

    Regards,
    Masahiro Suzuka
  • 0 in reply to Masahiro Suzuka
    Expert 1320 points
    Hi Masahiro&Nithin,

    About this question，Is there Any update?

    do all the calibration, the piont cloud still bent?

    Can anyone give me some advise?

    Thanks&Regards

    None