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:
- Automatically improved accuracy within single scans
- Improved frame-to-frame registration via accurate loop closure
- Available for download at www.dotproduct3d.com/targets
- Can be printed to different sizes, but larger tags will be recognized more readily by the software
- Place 2-3 AprilTags at the starting point of your scan
- Plan to return back to the same area at the end of your scan
- Scatter additional AprilTags throughout the scan
- Quantity is up to you (typically 5-20 total depending on scene size)
- Should be evenly placed throughout scene at varying elevations
- Also can be placed in difficult areas (i.e. empty white walls) to assist with tracking
- Initial 2-3 are most crucial
AprilTag Targeting for Loop Closure Procedure:
- Begin your scan in the area of your first 2-3 tags
- Turn the AprilTags orange while scanning (detected)
- If not detected easily, move in closer
- Turn all tags orange before moving on
- Pan through the scene in standard fashion
- Turn all areas of interest green/yellow to ensure quality
- Move about the scene in a loop to return back to the start tags
- Upon return to the start, turn tags orange again before finishing
- 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.
Pros / Cons and scanning Best Practices for Intel RealSense D415 and D435
The Intel RealSense D415 and D435 (as well as D435i) sensors are a great choice for scanning outdoors and/or in sunlight. However, as with all sensors they have both advantages and limitations and using scanning Best Practices is highly recommended. ...
Dot3D Tutorial: Registering Multiple DP Scans with AprilTags in Dot3D Pro
Please click below for a full video tutorial on this procedure: Dot3D Tutorial: Registering Multiple DP Scans with AprilTags in Dot3D Pro This DotProduct video tutorial walks us through the full procedure to register 2 DP scans to each other using ...
Which versions of Dot3D allow for use of AprilTag targets?
AprilTags can be used for loop closure (automatic single scene accuracy improvement by looping over unique tags multiple times) in any version of Dot3D with scanning capabilities enabled (Dot3D Scan, Dot3D X, and Dot3D Pro). However, to use AprilTags ...
Dot3D Tutorial (Dot3D Pro 4.0)
Please click below for a full length video tutorial covering our flagship Dot3D Pro handheld 3D scanning software. This video happens to be filmed from an Android phone equipped with an Intel RealSense L515 Kit, but almost all concepts also directly ...
How to Register Multiple DP Scans to Each Other
You have various options for linking multiple 3D scans into the same coordinate system: 1. Register using AprilTags in Dot3D Pro. Please see below for a video on this capability, available in Dot3D Pro 3.2 and up. Dot3D Tutorial: Registering Multiple ...