How to use Detect Markers Tool

This tool enables you to automate the process of placing control points into your images. All you need to do is prepare some suitable markers and place them in your scene before shooting and RealityCapture will do the rest for you. You can use the built-in markers' generator in the tool itself. To activate the tool, go to the ALIGNMENT tab, section Optional and click the Detect Markers button. The Detect Markers tool will show up in the 1Ds view.

Supported marker types

Markers are special high-contrast patterns printed on flat surfaces, whose shape allows them to be precisely located from almost any viewpoint. We generally recommend that the photographed markers are at least 100 pixels wide and it is endorsed for angle between camera marker and vertical shot to be as small as possible for markers to be recognized upon detection. For markers to be easily recognized it is endorsed not to edit them and leave the white space around them (buffer). It is also important to not cover them in any way, not even the white parts. RealityCapture recognizes few marker types and you can choose one of them before their detection:

• Circular, single ring, 12-bit is a circular target with a 12-bit data ring. The circle is divided into 12 parts.
• Circular, single ring, 16-bit is a circular target with a 16-bit data ring. The circle is divided into 16 parts.
• Circular, single ring, 20-bit is a circular target with a 20-bit data ring. The circle is divided into 20 parts.
• Circular, dual ring, 12-bit is a circular target with two 12-bit data rings. Both circles are divided into 12 parts.
• Square, April Tag, 16-bit (4x4 array) is a square target with a minimal Hamming distance of 5 between any two codes.
• Square, April Tag, 25-bit (5x5 array) is a square target with a minimal Hamming distance of 7 between any two codes.
• Square, April Tag, 25-bit (5x5 array) is a square target with a minimal Hamming distance of 9 between any two codes.
• Square, April Tag, 36-bit (6x6 array) is a square target with a minimal Hamming distance of 10 between any two codes.
• Square, April Tag, 36-bit (6x6 array) is a square target with a minimal Hamming distance of 11 between any two codes.
• Circular, legacy - This type is only useful for detecting circular, single ring markers printed by an old version of RealityCapture. The legacy marker types cannot be generated anymore.
• An illustration of a single ring, 12-bit circular target
• An illustration of a Square, April Tag, 16h5 target
  
  
  

  How to generate markers

  The built-in markers' generator enables you to generate a desired number of coded markers.
  Markers are then saved as a PDF file on an A4, A3 or letter size page(s).

  1. Choose the Marker type you wish to generate.
  2. In the Markers count, enter the desired number of total different markers to be created.
  3. In Markers per page choose desired amount of markers to be laid out on one page.
  4. Click the Generate button and choose a file name and location for the generated file.

  Procedure for the marker detection

  1. Click the Detect Markersbutton in the Constraints part of the ALIGNMENT tab.
  2. Select the Marker typeto be detected.
  3. Select the Required measurementsof each marker. Markers detected on a fewer images than the number specified in this setting are discarded. This option effectively filters out markers that are found in fewer than the specified number of images.
  4. Click on the Detect button to start detecting the markers in images.

  In order to detect markers in a subset of input images, select the required images first.
  TIP: Set Required measurements to a value greater than 1 in order to detect markers robustly and prevent a marker being detected by only one image.

  A new control point is created for each marker that has been detected, provided that there is no control point with the exact same name. Any existing control points with matching names are augmented with new measurements but keep all their other properties.

  How to detect ground control points

  Ground control points can be located via marker detection by assigning them a suitable name and running marker detection afterwards. It is also possible to change the type of the control point to ground control or ground test after the detection and set the specific coordinate system and the ground control points’ coordinates.