Innovation for the art & entertainment worlds
3d scanning is complicated. Do not let the manufacturers fool you. They want to sell scanners. What sells more scanners? The fact that people tell you that they do not have hours of post processing and multiple failed scans under their belt or the fact that they suggest that scanners are plug and play and the resulting scans are perfect every time?
The truth is that it is rare to get a 3d scan completely clean. Occlusion (the effect of one object in a 3-D space blocking another object from view) happens in almost all complicated scans. Noise creeps up in some of the best well thought out scans. Post processing almost always has to happen. In fact, some scanning bureaus “re-sculpt” details back into organic subjects. Sometimes I have even seen scans that have dimples and pore structure when I know darn well that their scanners do not have the sample pitch to accommodate that resolution.
I put together some tips though to make sure you can get the best from your scans.
1. Ensure the scanner is properly calibrated
Some manufacturers pre-calibrate their systems at the factory. If this is the case make sure you know the procedure they perform and check with them to see if they have a process to validate that calibration. Don’t take it for granted when you have to rely on the data. Good data is paramount in my opinion. Also, ensure that the manufacturer has a method to re-calibrate the system if its needed, if shipping is included, or if it will cost you anything.
If your scanner is calibrated by the user be aware that there are many things that can cause your system to go out of calibration. For instance impact can cause your system to go out of calibration. I was scanning an original brass maquette for a famous sculpture and I was involved in a fender bender. The scanner was in a pelican case and a driver hit me in my rear fender. Needless to say, the scan data was almost impossible to align and merge. Here, the optical CCD sensor was dislodged slightly. The scanner looked fine from the outside but it was not.
Extreme temperature can cause components to expand or contract. That can cause the system to go out of calibration. Most manufacturers state optimal operating temperatures. You would be best served if you work within those parameters. The truth is professional systems are amazingly intricate scientific devices. Treat them as such.
2. Learn how to control Light
A wise man once said “Of what use are lens and light to those who lack in mind and sight?” I’ve used both structured light scanners and laser scanners that have incorporated gain adjustments to acquire data in challenging lighting conditions. The results are most often more noisy and less accurate so be careful. Structured scanners are limited by the light the projecting source outputs and it’s contrast level. Therefore bright lights cause problematic noise to structured light scan data.
I find it much better to scan in a controlled environment, an environment where I can control the lighting conditions.
3. Keep it steady
Have a stable subject and a stable scanner. Minimizing motion is one of the most important factors in eliminating noise. At first, I was focused on ensuring that my subject was secure but if the scanner is on a less than robust tripod you are asking for added noise and lined artifacts in your scan. The longer the acquisition times the more motion matters. A scan of even a few seconds should still remain perfectly still for best results.
Not all floors are created equal. Floors are prone to vibration unless they are made of concrete. Keep ambient movement and traffic away. 3D scanning on shaky floor can yield bad results. Tell others to take a seat.
In our studio we use granite surface tables and metrology stands
4. Make sure your subject is properly prepared
Subjects that have multiple features represented for instance I’ve also seen the anomaly where high contrast colors (most often black and white) causes artificial features to form. For instance a subject that has white next to black will result in the black to be slightly raised in the 3d model. Subjects that are shiny, translucent, or transparent should be sprayed in order to scan. However, take care not to go too thick with the spray. I use Magnaflux Spotcheck Developer Spray. But I also have used Arid extra dry, Foot spray, or novelty white hairspray in a pinch. I have no problems with the cheaper methods.
5. Realize that data will most likely need post processing
I deliver my data without any smoothing. I think that it is a more accurate interpretation of the actual article. If the client asks for smoothing then I perform it upon their request. I most often 3d scan organic forms and my data is virtually noise free. I believe scans delivered in that manner serves my art clients needs better.
Most cheap scanners have automatic smoothing done without you knowing. This is to compensate for cheap components that inherently incorporate tons of noise in their data. If you choose you can also perform smoothing.
Like I said before most complex objects have occlusion. There will be some sort of reconstruction or hole filling in those instances.
Remove overlapping data the best that you can from multiple passed scans. Otherwise the merging process will calculate an “in-between”value and not produce the best results. Geomagic will actually average the two overlapping meshes together in some instances.
Remove un-referenced vertices.
6. Use the manufacturers recommendations
Scanners have recommended volumes. Scan within those limits. As a general practice I delete data at a scan’s furthermost limits. It aides in the alignment process. Subjects that have large features along with thin and tiny features also cause issues when scanned together. You cannot adjust focus to optimize both in a single scan. One will suffer. Pick one, scan the subject with the end goal of incorporating a great scan of the overall model. Remove the parts of the general scan that were not optimized in those detailed areas. Then go back in with better details segments, align and merge the two passes together.
7. Keep it clean
I would also refrain from scanning in dirty, dusty, or windy environments. Not only will wind most likely cause vibration but dirt and dust can land on your subject and cause bumpiness or fuzziness. If dust and dirt sneaks in crevices and intakes it may also damage your devices.
Great words of wisdom from Konica Minolta-
“3D scanning, while incredibly precise, will NOT result in a perfect scan of your model. You may certainly scan every possible detail and facet of your project, but time needed to compile and process this would likely invalidate your efforts and intent.It is better to learn the tool, establish an understanding and remain flexible.”
These are general rules of thumb for basic scanning methods. I’ve noticed that things like brighter lights and motion do not matter as much in photogrammetry methods.
Remember, we sell 3d printing and scanning equipment. I am a rep for Stratasys 3D printers and 3rivers 3d scanners. If you click on the store link you’ll also find some items there that may interest you. If you have any questions feel free to email me at firstname.lastname@example.org.
Thanks for reading!