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Camera Calibration / f and k1 value in calibration xml data of equirectangular image

« on: August 18, 2024, 11:55:51 AM »

I am currently working with 3D reconstruction using a set of equirectangular images and trying to see the calibration result.
Fortunately, I managed to export the calibration xml file using Python api

Code: [Select]

chunk = Metashape.app.document.chunk
cameras = chunk.cameras

for camera in cameras:
    if camera.sensor:
        calibration = camera.sensor.calibration
        calibration_path = f"DIR_PATH\\calibration_{camera.label}.xml"
        calibration.save(calibration_path)
and I got this xml file for example;

Code: [Select]

<?xml version="1.0" encoding="UTF-8"?>
<calibration>
  <projection>spherical</projection>
  <width>2560</width>
  <height>1440</height>
  <f>407.4366543152521</f>
  <k1>-3.5572726500569751e-322</k1>
  <date>2024-08-18T08:15:02Z</date>
</calibration>
I have two questions regarding this output.

1. Are the output values of f and k1 meaningful or just random?
2. If they are meaningful, how are these parameters used during projection? What do focal length and radial distortion mean in an equirectangular image?

I would like to know if there are any academic papers or blogs that can help me.