SCAN IN A BOX
Guide to the Ideal 3D Scan
Part II – Scanning procedure
- Mesh Generation;
- Post Processing;
1 . Acquisition
Once decided where to start the acquisition, the scan strategy will be very easy. It is advised to built a 360° panning shot of the object, taking the second acquisition after having rotated the object 25° about its vertical axis or after moving the scanner, using the LIVE view available in the software as reference (ref. fig. 32).
The scan can be continued using the same view selection method, taking care to ensure a certain sequentiality, such that a given acquisition partially overlap other previously acquired object parts. (ref. fig. 33).
Once a rough 3D reconstruction has been obtained, the scan can be improved by adding more views that correspond to some missing parts that can be due to undercuts, dark surfaces or parts of the object not framed previously.
It is advised to add every scan you may need in order to have a complete 3D model of the object (ref. fig. 34).
The crosshair is constituted by a green and blue square in the middle of the image and by a black line projected on the object. When the black line lays under the yellow cross in the middle of the green and blue square, the point beneath the yellow cross is exactly at the middle of the scan range (ref. fig. 36).
If the object is moved away from the scanner, the black line will move toward the external part of the cross-hair, the blue one (ref. fig. 37); if the object is moved closer to the object, the black line will move toward the inner part of the cross-hair, the green one (ref. fig. 38).
In this way, by observing the color of the box that is crossed by the black line is possible to set the wanted work distance: if the line is in the blue it means that the object is farther from the range image center, if it is in the green it means that the object is closer from the range image center.
PRO TIP! A wide and very detailed object can be scanned by exploiting Scan in a box versatility, by setting up two different field of work! The part of bigger dimension of the object can be digitized with a wider field of work. After that, it is possible to set the scanner for a smaller field of work. In this way you can scan the smaller object feature with a higher resolution.
Acquisitions of the same object made with different field of work does not prevent to align the Range Images (ref. fig. 40).
2 . Alignment
Switching between alignment and scan is useful only when in doubt about the correct object reconstruction. Once taken familiarity with the acquisition process, it will become more natural to acquire all the range images first and then work with the alignment tool on a Range Images sequence.
It will always be possible to complete and align the subsequent scans to a previous data set, for example to fill a missing information with an extra acquisition. It is recommended to use the alignment tool after having cleaned the range images of all the outlier points (ref. fig. 44).
3 . Mesh Generation
The Mesh is the first useful data that can be elaborated and exported in the available formats.
The Mesh generation is an automatic procedure in IDEA The Software : included in this command there are four profiles with different data processing parameters according to the type of the digitized object.
The four profiles include:
- Technical object - it is appropriated to maintain a high level of detail with a tolerance of 0.035mm.
The profile expect a mesh with maximum triangles in the amount of 500 000.
In the case of a mesh with a higher number of triangles, the software will decimate it automatically with a tolerance of 0.010mm. It also automatically applies a smoothing and it closes the smallest holes (with a boundary of less than 100 vertexes) (ref. fig. 48).
- Design object – the parameter are the same of “Technical Object” with the difference that it applies a stronger smoothing with a higher tolerance (ref. fig. 49).
- Small Artistic Object – this profile has a very high detail with a small tolerance (0,010mm). It applies a light smoothing and it automatically fills the smallest holes. It has no limits in the triangles number, so the automatic decimation is not applied. In this way it is possible to achieve the higher detail level and precision on the mesh (ref. fig. 50).
- Sculpture – this Mesh generation profile has a tolerance of 0.025mm, but always keeping the high details. The default settings does not apply an automatic mesh decimation (ref. fig. 51).
TIP! The parameters of the default profiles can be modified upon customer's need by expanding the Mesh Generation panel with the advance settings. Applying some filters during the mesh generation such as smoothing, detail tolerance, decimation and hole filling can make the following operation easier and speed up the following mesh post processing.
These commands can be applied individually in the post processing procedures that follows the Mesh generation.
4 . Post Processing
These operations should be chosen depending on the result to be achieved and they can affect more or less the 3d model.
The commands menu will be accessible after selecting a mesh.
In order to make the workflow faster and easier, the post processing commands are organized in the following order, although every command can be applied freely and they can also be repeated (ref. fig. 52).
This tool will also remove automatically all the small connected components of a Mesh that are disconnected from the main body of the object and that are so considered as separated entities.
This tool is mandatory in order to make the model ready to be 3d printed. It is advised to apply this command every time an operation of triangles removing and hole filling is applied on the mesh (ref. fig. 53).
Detect and repair intersection
By starting the tool, the command panel will open. Here you can chose which kind of operation apply on the Mesh: the simple selection of the intersecting triangles, that will highlight the intersecting triangles with red colour; the selection and cut of the intersecting triangles, that will create new holes; the selection with cut and hole filling of intersecting triangles, that will automatically close the holes created with an automatic fill. In order to have a quicker post processing procedure, it is advised to chose the third option. Otherwise it is possible to cut the intersecting triangles with the second option and then close the resulting holes in a following moment.
In order to have a quicker post processing elaboration, it is advised to select all the holes of the mesh by clicking “Select all” and then to proceed with the automatic holes filling with the command “Fill” (ref. fig. 56).
Otherwise it is possible to select a single hole or a group of holes by clicking on the voices on the list. If the options “Centre selected boundaries” or “Frame selected boundaries” are selected, it will be easier to locate the holes on the Mesh (ref. fig. 57).
It is possible to fill automatically the hole by browsing with the mouse the 3d model and by clicking on the hole border (ref. fig. 58).
Following these steps, a closed 3D model without imperfections is obtained. This data is already a really good solution and it can be exported in one of this available extensions: .stl, .obj, .ply , .off .
5 . SimplificationUnder this process called “Simplification” are gathered all the steps made on the mesh that (tend to) simplify the data.
Reduce noise on mesh
TIP! By selecting an area on the mesh surface, the noise reduction command will be applied only on the selected area (ref. fig. 60).
TIP! Simplification procedures are not supposed to be applied only after the post processing procedure. It can be strategically useful to make this simplification operations before completing and closing a mesh, bearing in mind the final purpose of the file that you're generating and modelling. For example a decimation that is done since the beginning of the work flow, with the knowledge of a maximum triangles number, can make the work quicker and reduce the computing time of the hole filling and other post processing procedure.