This article was written based on EXScanPro v3.7
When the very first frame is captured, a Bounding Box is defined. This box is a cube that encloses all the 3D space where scanned data can be saved.
Beyond the limits of the bounding box no scanned data will be gathered.
With no awareness of this phenomenon, this could lead to believe that an unexpected or undesired effect is taking place, like in the GIF below. This feature has an important role in ensuring the accuracy and quality of the scanned data, though.
It is a crucial factor that must be considered prior to any scan, specially for large objects. Otherwise, it might prevent the user from completing the scan.
Size of the Bounding Box
The size of the bounding box is defined by the following formula: Size of Bounding Box = Point Distance (mm) ⋅ 8192
Being 8192 a constant, the size of the Bounding Box is therefore determined by the selected Point Distance (or resolution).
The different sizes of the Bounding Box can be observed in the table below:
Resolution | Point Distance (mm) | Bounding Box size (mm) |
High | 0,2 | 1.638 |
High | 0,3 | 2.458 |
Medium | 0,5 | 4.096 |
Medium | 0,7 | 5.734 |
Low | 1 | 8.192 |
Low | 1,5 | 12.288 |
Low | 3 | 24.576 |
Therefore, the selected resolution has an impact on the size of the scannable 3D Space, being 1,638 meters and 24,576 meter the minimum and maximum sizes of the Bounding Box respectively.
Location and Orientation of the Bounding Box
The scanner position and orientation at the first shot, defines the location of the Bounding Box.
More specifically, the location of the scanner determines the geometric centre of the Bounding Box, while the orientation of the scanner dictates the direction of the Coordinate System (CSYS) as shown in the picture below:
Therefore, the position of the scanner relative to the scanned object at the first shot, sets both the location and orientation of the Bounding Box.
The clip below represents the position of the scanner inside a 8,192 m-sized Bounding Box, at the instant it is generated.
Beyond the limits of the orange box, no scanned data can be saved.
Object location inside the Bounding Box and where to start the scan
Since the first scanned frame defines the centre of the Bounding Box, it is convenient to consider where to start scanning.
The clip below shows the scanning of a car, which measures 4,78 m at a resolution of 1 mm (size of Bounding Box is thus 8,192 m).
Since the scan started at the front of the car, part of the object remains outside of the Bounding Box, being not scannable within the project.
A solution would be creating another project to complete the scan.
Another option would be starting over and selecting a higher point distance, so the Bounding Box size becomes bigger:
However, let's see now what occurs if the operator considers starting to scan on one side of the car:
If the scan starts at the proper location (i.e., close to the centre of the object) the Bounding Box can contain the whole body, so the object can be scanned within the same project:
Note: Markers and the Bounding Box
As you might already noticed in the first clip of this article, the Bounding Box affects only to 3D scanned data and markers can be scanned beyond its limits.
Please note that for EXScan Pro v3.6.0.5 software there is no limit in the number of markers that can be scanned. However, the size of the Global Marker File (GMF) can contain a maximum of 5.000 markers.
For EXScan HX v1.2.0.4 software the limit of the GMF is 20.000 markers.
Conclusion
The Bounding Box is a domain which encloses the 3D Space in which scanned data can be gathered.
The size of this box depends on the selected resolution, being its minimum size a cube of 8,192 m.
The position of the Bounding Box depends on the location and orientation of the scanner at the first captured frame.
Therefore, it is important to consider the best position to start scanning, specially for large objects.
The size of the Bounding Box has no relevance when scanning markers. Markers can be captured beyond the limits of the Bounding Box.