Time to scan some fish

08/03/2015

Rumor has it Artec scanners often work with really bizarre objects. Fancy scanning some fresh fish? You got it. Actually, this skill is more important than first meets the eye, and here’s why.

Fish is a good example of an object that changes its shape when moved, distorting alignment and registration. However, there are some simple tricks that make it possible to scan these kinds of objects.

Hang it

The easiest and probably fastest way to scan an object with changing geometry is to fix it so that it is possible to scan it from all angles. For example, you could hang it on a string. This way the object itself can rotate and you won’t need to walk around the object to scan it.

There are a couple of drawbacks to this method, though. Heavy objects may change shape as a result of their own weight. Also, the bigger the object is, the more difficult it is to lift and hang. But if the object is not too big, it’s definitely worth giving it a go.

In some cultures, looking at fish rotating on a string is believed to have a therapeutic effect, especially on the nervous system. Check it out:

Got a spare pane of glass?

If you do, use it for a fish scanning session. Put the fish on the glass to scan it from below. Make sure to have a reference object for a smooth transition from the underside to the upper, or for alignment if you choose to scan it in more than one go.

This method mostly works best for scanning objects with simple geometry, since curves and the transparent surface of the glass will limit the scanner’s movements.

Expanding the boundaries of a familiar feature

To fix discrepancies between two (or more) fusions with similar but not exactly the same geometry we have the Non-Rigid Alignment algorithm. Most users think that it only comes in useful when scanning people that move during scanning. In fact it can and should also be used whenever the object changes its shape between scans.

To use it, make several scans and run the Fine, Global and Fusion algorithms on each scan separately. The less the object changes its shape between the scans, the better. Then select all fusions, go to the Align section and select Non-Rigid Alignment. Mark the fused model which you want to leave unchanged as registered and start aligning all other fusions relative to it.

To speed up the process, you can erase some overlapping geometry, but try not to erase too much. In the end, all of the fusions will have a similar shape. Fuse them together, preferably using Sharp Fusion with the Small Resolution parameter (0.5 or 0.8).

Keep in mind, however, that Non-Rigid Alignment is the most time-consuming method and the measurements of the final model may not be 100% faithful to the original.

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