2D markers are created with an application called MarkerFactory. This application produces png files that include a rectangular 2D marker, as below:
These markers are then printed onto paper or card, and used on the screen.
Options to the MarkerFactory are:
–code number, the code value, as normal decimal number, default: 0–blocksize number, the size of each block in pixels, for minimum size use 16 (the default is 32).–division number, the number of rows/columns of actual data, default: 5-o filename, the output filename, default: code-XXXXXX.png, where XXXXXX is the number in the codeFor example to create the marker above (code 178), one would run:
MarkerFactory --code 178 -o code-178.png
The division parameter affects the amount of data that the marker can hold. Four bits are used for marker orientation, so the number of useful bits is:
division * division - 4
Marker size
The physical size of the markers is limited by how well the computer vision can determine the marker shape. This depends heavily on the type of display, display materials, and even part of the display. On MultiTaction hardware, the width of a single cell is around 5 millimeters. Four bits of the marker are used for orientation information. The table below lists some typical marker sizes and the number of unique markers they can represent:
| Marker dimensions | Unique codes | Minimum size |
|---|---|---|
| 3x3 | 32 | 3.5cm x 3.5cm |
| 4x4 | 4096 | 4.0cm x 4.0cm |
| 5x5 | 2097152 | 4.5cm x 4.5cm |
| 6x6 | 4294967296 | 5.0cm x 5.0cm |
The sizes shown in the table correspond to the default marker tracking parameters available in the MultiTaction OSD. If markers with different physical size are generated, the marker tracking parameters in the OSD need to be adjusted to compensate.
On the older (before 2012) MultiTouch Cells (MT320, MT460, MT467), one block needs to be typically about 1 centimer wide for the marker to work properly.
Marker Materials
Choosing the correct material for the markers is important to guarantee their correct operation. Usually it is possible to do quick test by just printing the markers on standard paper.
Different materials can be tested by obtaining a sample and placing it on the display. Then looking at the camera image visualization in the OSD, verify that the black regions of the marker appear dark on the camera image and the white regions appear white.
Care must be taken in verifying the behaviour using a real display since the cameras work on infrared spectrum, around 850nm wavelength range. It is not enough to produce a marker using black and white tones and visually inspect it and assume it works. It is possible to have visually black material that is completely reflective in the infrared spectrum and appears white on the camera image.
MarkerFactory application
MarkerFactory application is included with the Cornerstone software packages which are available in the Download section. The location of the application binary depends on the platform: