Calibration patterns
A calibration pattern is an object with a specific pattern that can be recognized by ScannedReality Studio to calibrate camera positions and orientations.
A calibration pattern is only required if you use more than a single camera.
ScannedReality Studio uses simple planar patterns which can be easily printed out. Read the sections below for how to create your calibration pattern(s).
Locating the pattern PDF
The first step in creating a calibration pattern is to locate the PDF file with the desired pattern. ScannedReality Studio comes with patterns for the following print sizes:
DIN A4
DIN A3
US Letter
Furthermore, the patterns come in “small” and “large” variants. The “small” patterns are suitable for small-scale camera systems, while the “large” patterns are suitable for larger setups. We recommend using the “large” variants for Azure Kinect and Femto Bolt camera systems.
Choose the desired print size and variant, and find the corresponding PDF in one of the following three ways:
Download the PDF file from ScannedReality’s website:
Get the PDF file from the installation folder of ScannedReality Studio:
On Windows: Open Explorer and go to the installation folder. This will be
C:\Program Files\ScannedReality Studiounless a custom folder was chosen during installation. In the subfolderresources\calibration_patterns, choose the desired PDF file.On Linux: Open a file manager and go to the installation folder. This will be a folder named
ScannedRealityStudioin your home directory, unless a custom folder was chosen during installation. In the subfolderresources/calibration_patterns, choose the desired PDF file.
Go through the guided recording setup in ScannedReality Studio. In the Sensor calibration step, click on “New calibration”, and then select the pattern with the desired print size from the drop-down widget. Finally, click “Open pattern PDF”.
Choosing the PDF page(s) to print
Each pattern PDF file contains 50 pages. To create a single calibration pattern, it is sufficient to print any single one of these pages, for example, the first one.
A single pattern is sufficient to perform camera calibration. However, we recommend using multiple patterns. This way, each calibration image will contribute more data to the calibration than with only a single pattern. This is helpful both to reduce the calibration effort and to record more calibration data for more accurate results.
For using multiple patterns, please make sure to print each PDF page only once. Each page has a unique pattern for identification. Seeing the same pattern twice would confuse the calibration algorithm.
We recommend to use as many patterns as can be comfortably mounted to some object that can be placed and moved within the camera system. For example, the patterns could be mounted to a tripod, or to a small cube or tower. Since all patterns may move individually during calibration, it is also possible to mount the patterns to multiple tripods or other mounts.
Note
As of now, the calibration algorithm expects all patterns to have the same format. Thus, if using multiple patterns, please use the same variant (such as “DIN A4 - large”) for all of them.
Printing the pattern(s)
The main requirements for a pattern are:
The pattern must be visible to all used camera types, including the color and infrared cameras.
The depth camera must properly observe the pattern’s material. It should not exhibit distortions, lack of depth data, or excessive noise for this material.
The pattern must be approximately planar. However, a slight, static bend is not an issue and will not negatively affect the achieved accuracy.
Each individual pattern must stay rigid (do not deform) during the calibration.
As the simplest solution, a pattern may be printed on a sheet of paper, which may be glued to a flat and rigid object such as a sturdy piece of cardboard or to a piece of wood:
Calibration pattern printed on paper, glued onto cardboard.
Please make sure that the printed pattern can be seen in all camera streams, including the infrared camera streams on Azure Kinect cameras. This might not be the case for all kinds of printers and inks; laser printers may work better than inkjet printers. To test this, have a look at a test print in the infrared stream of a camera. This could be done in the first step of the guided recording setup, or in an external application, such as Azure Kinect Viewer for Azure Kinect cameras or OrbbecViewer for Femto Bolt cameras.
For example, the two images below show the pattern visibility on a laser-printed sheet of paper, and on a computer monitor:
Visibility test of the pattern on a laser-printed sheet of paper: While there is overexposure in the infrared image at this (small) distance, the pattern is clearly visible in all cameras.
Visibility test of the pattern on a computer monitor: The pattern is clearly visible in the color image. In both the infrared and depth images, from this perspective there is a reflection that obstructs the view in the center, although the pattern is generally visible in both cameras.
If the printed pattern is slightly bent, this is not an issue as long as it stays rigid during calibration. ScannedReality Studio will adapt to this internally, and there is no advantage in having a perfectly flat calibration pattern.
If you would like to go for a more durable solution than paper glued to another object, then some options are to print the pattern on aluminum-based material (as for example used for outdoor advertising signs), or on wood. Print services for these materials can be found online. Make sure that:
The contrast between the white and black color is good (and that the white areas actually print as white; they are transparent in the PDF files),
That the result does not bend during use,
And that all cameras, including the depth and infrared cameras, have no trouble observing the printed pattern.
A calibration pattern printed on aluminum composite material, glued onto wood. This pattern file is currently not included with ScannedReality Studio.
Mounting the pattern(s)
Ideally, while a calibration image is being taken, all patterns should remain completely static. Thus, patterns should be mounted on a tripod or other kind of mount keeping them in place while recording an image, but allowing to move them through the recording volume between calibration images.
If using multiple patterns, each pattern may move individually between taking calibration images. In other words, it is not necessary for all patterns to keep a fixed relative positioning.
As an example of a suitable mount, this photo shows two calibration patterns on a tripod, where the tripod can be adjusted to change the pattern height and orientation:
Another way to mount the patterns would be a wheeled tower which can be moved through the recording volume. By placing patterns on all sides of the tower, each calibration image could add matches for each camera, which would result in very quick calibrations.