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Camera Calibration and Posing

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Overview

This section describes the process and best practices for calibrating your digital camera.
The resulting camera calibration values are used for accurate digital representation of your camera. These values are essential for the correct values of the camera position, orientation, and field of view.
The calibration process has to be performed only once per camera/lens combination. Resulting calibration values of your camera+lens can be saved as a calibration preset and re-used in your future projects.

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WARNING
Skipping the camera calibration and posing step can lead to misbehaviour of safety algorithms and cause potential damage.
Generated travel positions might become not representative of the physical camera position and travel path.

Recommendations

For the best possible automatic capture for calibration it is recommended to:

  • Using prime lenses below 80mm in focal length.
  • Use good ambient diffused lighting.
  • Aperture or F-stop number of f8+. Make sure the calibration chart is in full focus.
  • Make sure the calibration chart is fully visible on all images taken.
  • Calibration chart has to be fully mounted onto the turntable extension. Make sure the chart doesn’t vibrate or shake during the capture process.

New Calibration setup

In the ‘Calibration & Posing’ tab of your camera (Agnostic or Tethered) navigate to a ‘New Calibration’ window.

arago calibration 1

 

1. Place the calibration chart

on the second level of the turntable extension (at 60cm/23.6″ height). Follow the installation steps outlined in the Turn-table extension installation guide. Make sure the chart and the turntable extension are fully mounted and are not causing vibration/shakiness during movement.

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NOTE
Inspect the calibration chart for any visual deformations and dust or stains. The surface of the chart has to remain perfectly straight and clean to achieve accurate calibration results.

 

2. Mount the camera

on Arago horizontally/landscape with the provided bracket and the shoe mount. Make sure the camera is visually centred on the tilt element. Use the sliding bracket to re-adjust and secure if necessary.

arago camera bracket 4

 

3. Use the manual motion

control along with a camera live view to drive Arago until the calibration chart is fully framed in the camera’s field of view. Make sure the chart is front-facing the camera. Allow for some free space above and below the chart to eliminate the possibility of clipping the view.

arago calibration chart framing

 

4. Start Capture for Calibration

Make sure you have a clear scene (no positions or models) and Click on ‘Start Capture for Calibration’. This action will load a list of positions along with a chart 3D model acting as a scan volume and activate panel for starting the capture. Make sure everything is in place and begin capture for calibration by clicking ‘Play’ in the capture panel. This process will take around 5 minutes.

 

5. Start Calibration from Images

When the image capturing process is finished, move on to ‘Start Calibration from Images’ and select all the images taken. At this point, it is recommended to inspect images for any out-of-focus or miss-framed images and discard them from the selection. The calibration process with automatically begin after selecting images. This process might take up to 10 minutes depending on the power of your computer. During the calibration process, you can observe the calibration results per image and detected markers. It is possible to identify problematic images by observing individual ‘Reprojection Error’ values. In case any major error value is present, repeat the capture process.

arago calibration 3

 

6. Evaluate Calibration result

When the calibration process is finished, the total result is shown. The important part at this point is the ‘Reprojection Error’ shown in bold. The smaller the reprojection error is the better. The result is color-coded in the following way:
Green – a good reprojection error of <1
Yellow – an average reprojection error of 1-3. In case you observe digital camera placement or field-of-view discrepancies in comparison to the physical camera – try re-starting the process.
Red – a bad reprojection error of >3. It is recommended to restart the calibration process.

arago calibration 4

 

7. Save Calibration

At this point, you have an option to export the calibration file for later use or save it as a ‘Calibration Preset’. The preset will be available for later use within the ‘Calibration Preset’ dropdown in the ‘Calibration & Posing’ tab of your camera (Agnostic or Tethered). It is recommended to name the calibration preset in a way that describes your Camera+Lens combination well.

 

8. Camera Posing

In order to pose the virtual camera in relation to the physical one, it is required to take a single image of the positioning marker placed in front of Arago’s X-axis as shown in the image. Manually drive Arago unit by using the software motion controls until the marker is fully visible by the camera and is targeted at a slight angle. Placement of the camera for the image doesn’t have to be too precise.
In the ‘Calibration & Posing’ tab of your camera (Agnostic or Tethered) click on a ‘Pose Camera from a Marker image’ button and navigate to the image taken.
It is important that you don’t move Arago after the image has been taken.

At this point the virtual camera position and field-of-view are re-adjusted and the calibration process is completed.

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