Here are some general tips and information about scanners that I’ve compiled over 3 years as a scanning technician for aerospace investment castings, browsing this forum, and having my Pop2 for about a year now.
- Make sure you’re in a proper lighting environment – sunlight, incandescent bulbs, some LED’s, etc. will emit infrared and interfere with POP/Range scanners. No Structured Light scanner (all of Revopoints’ Products) will do great outdoors -EXCEPT on overcast days or evenings. When I scan, I will turn off all lights that are unnecessary or overhead of object.
- Scanner uses two sensors to make measurements using trigonometric algorithms. No scanner can sense a feature if both sensors cannot see the feature (think of your eyes and putting a piece of cardboard between them). To get past this limitation – rotate the scanner vertical (180 degrees) so get scans of tight areas.
- Moving the work piece, in my opinion, is better than moving the scanner as moving the scanner by hand is shaky and operators can drift in/out of the scanning volume (in and out of focus). However, depending on the subject – you may have to move the scanner.
- Light used (Infared vs. Bluelight) has no impact on accuracy. However, there is a major impact on noise rejection – which can greatly improve accuracy. Blue light is the least prone to light interference from the environment and thus the best wavelength to use for scanner.
- Speaking of accuracy – accuracy has to do with optics (camera/sensor lenses) and nothing else. Unfortunately, in our price point we have cheap optics – but issues of optics are corrected with a proper calibration. To increase the accuracy of scans, you have to increase the pixel density per volume (this is reported as point distance on Revopoints Specifications). On Revopoint systems our lenses, and thus, “Resolution” or accuracy is fixed.
- Range has a point distance of 0.3mm
- Pop2 has a point distance of .15mm
- Mini has a point distance of .05mm!
This means the smallest feature (in theory) each scanner can infer is .3mm, .15mm, and .05mm) though it will probably be more likely double or triple this number in reality. With everything else in the world there are tradeoffs. Higher resolution means you need a bigger camera (more Pixels) or have a much smaller scan volume. On the flip side, having the ability to scan a large area (Range) comes at a cost of less resolution/accuracy.
- To get the highest resolution/accuracy as possible:
- Reduce light pollution
- Keep lenses/scanner clean, dirty or scratched lenses will impact scan.
- Ensure you’re in scan volume (“excellent distance” in Revoscan software).
- Adjust exposure so that some areas are just overexposed – but not entirely red.
- Scan in High Accuracy mode.
- Marker scanning (using points) may increase accuracy if Revoscan uses photogrammetry in conjunction to structured light – but I do not believe they do. However, ATOS by GOM/Zeiss does.
- Avoid scanning layers more than once – but overlap scans to improve tracking. Unfortunately, when meshing in Revoscan – the software cannot do a gaussian best fit. Instead of averaging the surface data – double scans will confuse and ruin scans.
- Attempt to collect as much data as possible – filling holes injects “Fake” data into the scan – useful for aesthetics – but not for engineering work.
- In mesh/point cloud editing – do not use smoothing algorithms or point reduction as this alters data/deletes data.
- Make sure your scanner is calibrated to the advertised point distance or better. Poor calibration will introduce artifacts and may make merging scans/meshing difficult or impossible. You should check calibration regularly or if the camera is transported, dropped, shaken, etc.
- To scan Symmetric or very flat components/items:
- Use marker mode only
- To scan large Items:
- Use body mode – it reduces accuracy but increases scan volume.
- To scan shiny/metal items, you must paint/coat item in matte white or grey. To do this:
- Use scanning spray (most expensive)
- Mix talc & isopropyl alcohol and use spray bottle (most practical)
- Mix ~25% finger paint and 75% isopropyl alcohol to use with air spray gun (most practical for large pieces or for those who scan a lot/often).
- *Note over spraying item will add material to the item – and by doing so you may reduce accuracy of scan if scanning for quality/reverse engineering purposes.
- *Talc or fingerpaint should be removable with either water, alcohol, or mineral spirits if necessary (depending on material of item).
- Random tips/tricks:
- Markers/point can be used even in feature scanning mode to help merge scans by marker.
- Scanner supplied stands/handles use standard ¼-20 hardware which can be used with any standard camera tripods or accessories (steady cams, etc.).
- When not in use – store the camera in its box!
- Experiment with new software:
- GOM Inspect is freemium – used in Aerospace/Automotive.
- CloudCompare is popular & open source.
- Meshlab
- Others (search the forum).
- Troubleshooting:
- Spiraling scans
- User error caused by scanning symmetric or flat surfaces – use markers and marker mode.
- Bumpy meshes
- Light pollution/noise – check surrounding lights.
- Check exposure.
- Check calibration.
- Distorted point cloud/trouble merging scans:
- Check calibration.
- Reduce “scan size” – longer scans tend to drift (ie curl) due to calibration/tracking error that gets stacked up.
- Small features not meshing
- Meshing algorithm cannot infer some small features vs. area of less-dense data.
- Try a different piece of software.
- Having a difficult time scanning and getting data:
- Check light pollution
- Check calibration
- Check exposure
- Check that both sensors can “See” the feature.
- Spiraling scans
