Posts tagged scanning

Revision of scan results

As promised, we would give the summarized results for the two scanning sessions that we had: with CT scanners and with Artec Spider scanner.

Part of the results of the latter unexpectedly disappeared during the post-processing. The scan which promised the most for us, Hermione handle detail, was among the missing files. We hoped to get better results of the floral ornament and combine it with the CT-scan body, only the chosen comparison model and Harry survived.

Kam artec spider

As seen, for the comparison we chose the finest model we had. The lice-comb teeth were approximately 0.5 mm diameter with even smaller gaps between them. Due to this, the scanning technique used by Artec Spider could never achieve a proper result: too much was not visible, even with the precision of 0,05 mm. In other words, the grid which the range finding device projected could not be interpreted in the gaps and the result was a block with a texture instead of a comb. Moreover, looking at he scan of Harry we can see a big inconvenience for us: only the outer surface and the sections at the breaks were captured. Moreover, the cracked surface texture was not captured, because we got the file only in a mesh file.

artec scanner harry

Therefore, it would be expected that this problem would not be so apparent in CT-scans. This technique captures the sections of the object, instead of making an interpretation of surface. Just then these sections are interpreted into 3D files. However, the precision of 0,3 mm proved to be insufficient for the artifact we chose:

macro CT kam

As seen, the result was a more consistent file, which could actually be printed. Nevertheless, it was far from what we would call sufficient. Expecting this, we also made micro-CT scans of the object. The sneak-peaks of the object in the lab itself looked very promising. Yet our and publicly available computers could not handle the size of the data set (over 2000 sections!) and could only give results in the lowest resolution, leaving us with the following model:

micro kam

As seen in the picture, the separate teeth are clearly visible, although the main body is missing. This can be easily solved if the used computer has 16GB RAM, since we could get a proper model in Avizo a few moments before it crashed due to memory insufficiency.

To conclude, only the micro-CT scanner offered the sufficient results for the compared artifact. The Artec Spider is very interesting if surface detailing in necessary or if textures/colors have to be captured. However, if not enough scans are made and combined, you will get an object lacking details, thus resulting in incredible amount of work hours in post-processing. Another solution for this would be to make CT-scans and combine them with the Artec Spider scans only for the details.

Artec Spider 3D scanner

While still being occupied with the processing of the CT-scans, the first impression was that it wasn’t as easy and accurate as we expected it to be. Maaike had reserved the Artec Spider for Friday for another project. We wanted to see if this scanning technique gave a better or different result then the CT-scanners. We were lucky that this was possible.

The Artec Spider is a scanner for small objects that captures really complex details and color. It has an accuracy up to 0.05 mm.

We scanned three objects:

  1. The comb, because this object is the only object that was scanned by the macro and micro scanner. Scanning this object with the Artec Spider will show the difference between these three scanners.
  2. Hermione, to see if the accuracy of details is better with the Artec Spider.
  3. Harry, to see if with this technique the break lines and repaired break lines will be visible
    In the files from the CT-scanner the repaired break lines weren’t visible and the break lines were given an arched shape.

The objects and the scanner had to be moved/operated by hand, since the objects were so small. For the comb this wasn’t a problem because we put it in a paper cup and turned that around. The scanner has problems with really small or big gaps. The small gaps in the comb were too small, in the model there was a relief instead of gaps.
The problem with Hermione was the big gap on one side. Because of the gap the model had a lot of failures. We tried multiple ways of scanning. Eventually we scanned only the handle, by making multiple scans from different angles and combining them together.
Because of the problems we had with Hermione we decided to fill Harry with a napkin, so that no problems would arise from the difference in distance. This went ok, only afterwards the napkin had to be deleted.
The results of processed 3D images will be posted later.

© 2011 TU Delft