Using AprilTags for Loop Closure in Dot3D

Using AprilTags for Loop Closure in Dot3D

AprilTag targets will automatically improve the accuracy and quality of your data whenever you loop over them multiple times within a single scan. This "loop closure" functionality does not require any additional measurement or manual input, and is therefore recommended whenever possible. Even something as simple as placing a single AprilTag at your start (and end) point is helpful, although more tags are recommended when possible. Please see below for more on this workflow:

Basics of AprilTag Targeting for Loop Closure:
  1. Automatically improved accuracy within single scans
    1. Improved frame-to-frame registration via accurate loop closure
  2. Available for download at
  3. Can be printed to different sizes, but larger tags will be recognized more readily by the software
  4. Preparation:
    1. Place 2-3 AprilTags at the starting point of your scan
      1. Plan to return back to the same area at the end of your scan
    2. Scatter additional AprilTags throughout the scan
      1. Quantity is up to you (typically 5-20 total depending on scene size)
      2. Should be evenly placed throughout scene at varying elevations
      3. Also can be placed in difficult areas (i.e. empty white walls) to assist with tracking
      4. Initial 2-3 are most crucial
AprilTag Targeting for Loop Closure Procedure:
  1. Begin your scan in the area of your first 2-3 tags
  2. Turn the AprilTags orange while scanning (detected)
    1. If not detected easily, move in closer
    2. Turn all tags orange before moving on
  3. Pan through the scene in standard fashion
    1. Turn all areas of interest green/yellow to ensure quality
    2. Move about the scene in a loop to return back to the start tags
  4. Upon return to the start, turn tags orange again before finishing
  5. OPTIONAL/RECOMMENDED: Mimic this procedure on a smaller scale during the scan with other tags scattered throughout different areas in the scene
AprilTags can also be utilized for scale bar and survey targeting, which do require additional input of known measurements/coordinates to add even higher accuracy/confidence to the data. Please click here for a video tutorial on these more advanced workflows.

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