Marker Selection

VDA Calibration Board

An example of a VDA 4-point calibration board is shown below. Calibration boards are available in sizes A0 - A12, you can select the appropriate size calibration board according to the test scenario. Typically, the calibration board should be 1/10 - 1/2 scale size in the camera view.

VDA devices are shipped with calibration boards of the appropriate size. If you need a calibration board of a different size, please contact RVBUST sales.

Measurement Marking

Clear target markers are required during VDA system measurements. The priority order for selecting markers is as follows.

• If it is possible to paste or paint the speckle patterns, it is preferred.

• If it is possible to mount or fix the measurement target marker, mount the marker.

• If it is not possible to paste or paint the speckle patterns, or to mount a target, the texture-rich area of the target plane can be selected as the POI/ROI for analysis.

Ideally, the target marker should uniformly contain both light and dark areas. The commonly used marking patterns include VDA Code, sprayed speckle pattern, marker-painted pattern, and natural texture pattern.

• VDA Code

  VDA code has the best performance and fastest speed for VDA analysis algorithm. Before use, print the VDA code at a ratio of 1:1 and paste it flatly on the surface of the measured object.

  

  The speckle diameter of VDA code should be selected according to the object distance and lens specifications, see the following table for data reference. When a VDA device is shipped, it is equipped with corresponding specifications of VDA codes and speckle stamps, which come in different sizes and particle sizes. If you need a VDA Code of another size, please contact RVBUST sales.

  Object Distance (m)	1	5	10	20	50
  Lens/Speckle Size (mm)
  8	2.2	10.8	21.6	43.1	107.8
  12	1.4	7.2	14.4	28.8	71.9
  16	1.1	5.4	10.8	21.6	53.9
  25	0.7	3.5	6.9	13.8	34.5
  50	0.3	1.7	3.5	6.9	17.3
  75	0.2	1.2	2.3	4.6	11.5
  135	0.1	0.6	1.3	2.6	6.4
  200	0.1	0.4	0.9	1.7	4.3

• Sprayed speckle pattern

  Speckle patterns can be made by spraying paint or pigment. The selection of speckle diameter is based on the same table as mentioned above. During spraying, white paint is first sprayed onto the surface of the specimen as a base color, followed by the spraying of black paint in a particulate form. This results in a surface with a uniform black-white speckle pattern. Before spraying, the nozzle can be irregularly damaged. By adjusting the degree of nozzle damage, the shape of the damage, and the spraying distance, the size and density of the spray particles can be controlled. Additionally, a template stamp with white powder can be pressed onto the surface of the specimen to obtain a clear speckle pattern.

  Sprayed speckle patterns are commonly used in material tensile testing.

  

• Marker-painted pattern

  Mark the target manually with a marker.

  

• Natural texture pattern

  For targets where it is not possible to manually attach VDA codes or add marking patterns directly, natural textures can also be sought. For example, the surface structures and textures of buildings, bridges, and engineering facilities. Taking the building in the following image as an example, the black-white transition at the edge of the window frames can be chosen as the marker.