Full UI - Camera Bar to Main
This page describes how to calculate the witness to main calibration when using the Full UI. There are two different methods available, the LiveUpdate method and the Chart based method. The LiveUpdate method generally gives better results and is recommended
The LiveUpdate technique is the preferred method of calculating the witness to main relationship. It works by using the features detected in the tracking environment as well as any fiducial anchors that are present to align the camera bar and main camera. The technique will work without a fiducial anchor being present, but it is strongly recommended to use one as it will vastly simplify the procedure.
- Start the system tracking
- Position a fiducial anchor in the environment and make sure it is detected by the camera bar
- Pan/tilt the camera or translate it, this allows it to generate some additional tracking points
- Position the main camera so that it can now view the fiducial anchor
- From the Top Menu Bar choose Devices>Main Camera>LiveUpdate
- In the augmented reality view the point cloud will be displayed over the main camera image if the step is successful
- Return to the Devices>Main Camera>LiveUpdate option and disable it
The following video covers the entire process
This is an alternative technique that utilises a calibration chart. It involves taking a series of pictures of the chart while it is in view of both the main and witness cameras to calculate how the cameras are positioned relative to each other
While this method is perfectly valid we typically advise to use the liveupdate method as it allows more flexibility in the mounting of the Ncam camera bar, the chart based method requires the chart to be visible in both cameras at the same time, meaning this technique won't work if the camera bar is tracking the ceiling for example.
- From the top menu bar select Devices>Main Camera>Camera Bar to Main Relation
- The camera relations view will displayed
- From the dropdown select the chart you are using, the A3-1 is recommended
- Press Start
- Position the chart so that it is seen by both cameras and the coloured pattern overlay is displayed on the chart
- Press F12 or click the Use Current button, to take a picture, repeat this until you have around 10 pictures. The number of images taken will be displayed in the "Images" field
- Press calibrate
- A calibration error value will be displayed, it will be colour coded depending on quality
- Press Save to confirm the calibration, pressing cancel will exit without saving
If a mistake has been made, pressing "Reset" will set the picture count back to zero
The values generated from the calibration are displayed within the system status tab of the GUI. They are nested under the Witness-Main Relation > Rigid Transform drop-down. The values are user editable, so some care should be taken to not accidentally alter them. A Save and Load button are provided here also, these allow the current values to be saved as a global default
It is generally good practice to check the result of the witness to main calibration after conducting any of the methods for calibrating it
The most obvious feature of a bad witness to main calibration is the Ncam cube not being correctly aligned with the selected zero point, when the zero point is in the centre of frame
Additionally the Ncam cube will move inconsistently with the camera
Observe how in the above image the axis of the zero point are not consistent between each image
The most straightforward way of doing this is by using the “image modelling view” (Shortcut - F8).
The image modelling view allows the user to view the position of the zero point from both the witness camera perspective and also the main camera perspective. This means that if there is a discrepancy between the two views then the calibration has not been successful.
To see a view from the main camera in the image modelling view, press F. This will take a snapshot from the main camera which can be viewed in the Main camera Tab of the filmstrip
A quick, but less accurate way of checking the witness to main relationship is by using the 3D view (Shortcut - F6).
In this view the camera bar and main camera are represented in 3D, their positioning should be correct relative to each other. This technique while convenient does not provide a very accurate way of checking the alignment, and should not be relied on.