Artec Spider II is a structured light scanner renowned for its capability of achieving extremely detailed meshes, especially when it comes to small objects with intricate geometry. However, if you wish to achieve fine resolution (as fine as 0.05 mm), there are certain rules that should be followed. . The most important are these:
- Geometric Detail Requirement: The object's geometry should contain features that are sub-millimeter in size to fully utilize the finest resolution setting and justify its application.
- Optimal Data Capture: The user shall employ the maximum amount of different scanning angles in order to make better distribution of structured light pattern and to ensure complete data capture.
In this article we will explain in detail the main aspects of scanning and processing using two objects. Both of them are rings, but one of them contains a rich portion of intricate geometry.
The other ring is less intricate, it has more smooth geometry. The only intricate part is a small cylindrical-shaped area with a stone surrounded by little metal “bumps”.
Let’s observe the difference in the approaches.
Object and scene preparation:
First of all, since both objects contain lots of shiny areas, it is essential to apply a scanning spray beforehand. For small objects we recommend using a system like an AirBrush – this one is capable of application of a quite thin yet effective layer of coating. Alternatively, you can use something similar to AESUB diamond spray since the size of spray particles is small enough to make sure that it won’t significantly change the geometry of your part.
Second of all, positioning of the object. Since Artec Spider II has tremendously improved geometry detection compared to its predecessor (Artec Space Spider) and increased FOV, it is beneficial to strategically add some geometry and texture features to your scene. Feel free to experiment with the set-up, here is an example that works
The setup utilizes the wooden texture of the rotation table plus some geometry objects to support further Global Registration (GR). In order to achieve the required mesh resolution, please keep in mind that added objects shall remain still relatively to the object that you scan. In other words, please pay attention to vibrations while you rotate the table and choose slower rotation speed that assures scene position. If you are not sure about this point - feel free to put the additional objects on blu-tack adhesive putty. It will eliminate the vibration, keeping the scene in the correct position.
Scanning settings:
Please pay attention to the scanning parameters, particularly the Geometry Gain slider. Since we are scanning a quite challenging object, make sure that the Gain value gives you a good coverage and absence of overexposed areas. Please activate the checkbox Overexposure indicator and adjust the Geometry gain.
Not OK
OK
Regarding the Switch gain every frame option - this automatic tool was designed to scan high-contrast objects, or for the situation when it is difficult to define the proper value of the gain. We don’t recommend using this functionality when aiming for extreme resolution. Scanned data will be more dense if the correct Geometry Gain value is chosen manually based on the overexposure indicator.
Scanning technique:
Another very important thing that you need to do when scanning such objects is the quantity of scanning angles. This means that it’s not only the object that needs to be moved by rotating the table, but the position of the scanner shall also be altered. Use your wrist actively to employ more scanning positions.
In fact, it’s always a good idea to use your wrist and your arm to make more scanning angles. However, it becomes more critical when it comes to scanning for extremely high resolutions.
Another very important aspect that directly affects the quality of your data is the scanning distance. During scanning, always aim to keep your object within the green zone.
Not OK
OK
Surely, if the object turns orange or blue for a fraction of a second (e.g. when you change the position of the scanner) it is not critical as long as the absolute majority of the frames are captured while the object is in the green zone.
To summarize, the main objective is to have the object scanned from all sides using different scanning positions maintaining the correct scanning distance. Aim to have the object and the background features in the field of view, otherwise the features are useless for tracking and GR.
Additionally, in order to have the object fully scanned, we recommend performing 3-4 separate scan sessions using different initial object orientations.
Processing:
In order to fix minor misalignments in the scanned data, we advise to perform Global Registration (GR) in Separate mode for all individual scans.
In this case the frames will be registered only inside their scans, without intermixing between the scans. If you used both texture and geometry as additional features, the most reliable way is to choose Features: Geometry and texture and check the Focus on geometry option. By default, G+T prioritizes the Texture over geometry. However, since the object itself contains rich geometry which could be detected and registered on Spider II data, enabling Focus on geometry increases the importance of Geometry features.
Next step is to delete all except of the object from all the scans in Editor. If it’s more convenient for you, use the Points render mode.
And align
Since the object is small and geometry-rich, it is advisable to align the scans in Manual mode, placing point pairs on distinctive features of the object.
Why don't we recommend auto alignment in this particular case – this tool uses Texture for alignment. Since geometry features in this case are more pronounced, manual alignment is faster and more effective.
The next step is to perform GR for all the scans so they can be calculated and compose the whole object. Here are some important things that you can do in order to improve the registration results.
If you have applied GR in Separate mode for all the scans that you are working with, it is advisable to use Lock frames feature before applying the final Collective GR. Regarding the GR itself – here we don’t have any texture features to support the GR, so it makes more sense to choose Features: Geometry. Please don’t forget to choose Registration mode – Collective.
Why application of Lock frames is a good option: since we have done initial GR in Separate mode, our scans have quite good registration between frames because we performed GR using the object + features from the background. Our goal now is to make sure that the well-positioned frames from Scan1, Scan2 etc. remain in their places, and that is why it makes sense to use Lock Frames. This feature, as the name implies, locks frames inside the scan, but the scan itself can move towards other scans.
Regarding the quantity of frames, the main objective is exceptional coverage. Do not hesitate to be generous with the frame count. For example; exceeding 2000 total frames, as was done for this ring, is perfectly acceptable.
The next step is Fusion. The Artec Spider II, unlike its predecessor, is capable of delivering the data that can be fused with the resolution finer than 0.1mm. In this case we will employ 0,07mm
If your data contains an insignificant amount of frames with higher error, feel free to install the Error threshold.
Here is the resulting mesh:
Here is the difference between two meshes from the same data:
Fusion 0.1mm
Fusion 0.07mm:
As you can see, some areas are better pronounced and some small features are more distinctive.
In a nutshell, there are two main conditions to be fulfilled if you want to achieve extremely high resolution:
- The object's geometry should contain sub-millimeter geometry features
- The user shall employ the maximum amount of scanning angles in order to make better distribution of structured light pattern and to ensure complete data capture.
If the second condition is not fulfilled, then there is a high risk that the mesh will contain artifacts caused by structured light lines.
Lines on the planar surface (insufficient data, low quantity of scanning angles):
No lines on the surface (sufficient data, enough scanning angles)
Let’s now observe the results for the second ring, which doesn’t contain enough features for achieving the high resolution mesh.
The workflow here is completely the same as before:
- Preparation: Affix the object, apply scanning spray and place some additional geometry and texture features on the scanning scene.
- Scanning: Choose the correct Geometry Gain and use active wrist rotation to achieve maximum scanning angles.
- Processing: Perform initial GR in Registration mode - Separate, Focus on geometry ON; use Editor to delete all unnecessary parts of the scans; align in Manual mode and perform the final GR in Geometry mode with Lock frames applied.
However, when it comes to meshing your data using 0.07mm resolution, you can observe the “orange peel” effect on the object.
Generally this defect is not something critical. However, if your object doesn’t correspond to the 1st condition, meaning that your object doesn’t have sub-millimeter geometry features, then it makes sense to limit the Fusion resolution to 0.1mm.
As shown, the 0.1 mm result is smoother. Additionally, the difference in the most intricate areas is barely noticeable and the features are still there.
| Mesh resolution 0.07mm | Mesh resolution 0.1mm |
Here are two more objects for your reference.
The quarter dollar
Mesh with resolution 0.05mm
And another ring with intricate carvings.
Conclusion: achieving the mesh resolution finer than 0.1mm requires sub-millimeter geometry features on the object itself and increased amount of scanning angles.
If the object lacks fine geometry, it is far more effective to limit your mesh resolution to 0.1 mm. This value is sufficient for representation of quite fine details while avoiding defects like the orange peel effect and maintaining a dense, high-quality mesh structure.
In case you experience any issues with your Artec 3D scanner or require technical assistance with your device or Artec Studio, in the first instance please contact your local Artec dealer/distributor directly. You can also contact the Artec Support Team by clicking on "Submit a request" button on the bottom right part of the screen or by emailing support@artec3d.com