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beginner_mistakes

This page explains some beginners mistakes based on the outcome and points to potentional scanning mistakes.

When you validate your scan result it is important to look at the scan result. This may sound obvious but what happens with many beginners is as follows: You do your first scan. It is full of holes so you increase the “interpolate” “smooth average” and “smooth median” values. Now your result looks lots better. No problem with that but… David remembers this setting and you are likely to foreget you changed them.

So the first thing you should do before discussing your scan quality is:

  • Set interpolate to 0
  • Set Smooth Average to 0
  • Set Smooth median to 0

Now look again at the 3D image and see your scan result. If you are not satisfied maybe one of the descriptions below will help you out. Remember this is a guide for newbie“s who has bad scan quality. So if you are trying to scan more advanced things you will be requested to scan simpler things.

Scan Quality is simply poor.

There are many things that interreact with each other. So it is not easy to say what is causing your problem. Below is a list of things you could look at.

The object to scan.

  • Is it shiny? If yes take another object. (Shiny makes things more complicated because of the laser reflections)
  • Has your object deep cuts or a complex overall shape? If yes take another object. ( Deep cuts makes it hard to focus the laser and makes it hard to get enough measure ponts)
  • Does your object fit into the scanning panels? If not take another object. (the more your object is away from the corner the less accuracy you will get)
  • Is your object smaler than half the pattern you use? If yes get a bigger object or a smaller pattern.

Your scanning corner.

  • Is your Corner exactly 90°? If not fix it.
  • Is your pattern wavy? If yes fix it.
  • Is your corner stable? If not fix it. (Your corner should not move during a scan)
  • Is your corner shiny? If yes fix it.
  • Is your corner in a room that can be darkened? If no move to a place where you can darken the room.

Your laser setup.

  • Is your laser focusable? If yes focus your laser on the object you want to scan. Focus the laser at the midle of the object while holding it at the position you use during scanning.
  • Is your laser moving position during the scan? Do not move the laser during a scan. Moving the laser means you need a better setup (for instance 90° listakes become worse)
  • Is your laser moving lineair? Unless you have a good device that guarantees you a good leneair movement replace it by a rotating setup.
  • Is your laser line wide? How wide? If you are reading this and your laser is not wider than 5mm the problem is very unlikely to be the laser width.
  • Has your laser line distorsion? If so clean your laserhead with glass clean product. A bit distorsion is not a problem but to much will impact the quality.

Your camera setup.

  • When there is no object to scan do you only see the pattern and only the pattern? If not move the camera to a better position.
  • Do you use digital zoom? If yes turn it of and move the camera if needed.
  • Is your camera stable? If not fix it. (Your camera should not move during a scan that is from calibration till you last scan is done)
  • Is your camera in a higher resolution then 640×480? If yes put it on 640×480 with the highest rate you can have. (Do not foreget to recalibrate)
  • Is your contrast high? Decrease the contrast. A high contrast introduces lots of noice.
  • Is your exposure rate low? Increase the exposure rate. In a dark room you can go up to 1/16
  • Is your camera focused on the object you want to scan? If not fix it.

If all this is ok you should get a good scan or you should be able to ask a more specific question.

The shape of the scan is ok but the surface of my scan does not match the surface of my scanned object.

Look at the “smooth average” and the “smoot median” values. If you want to know your scan quality these should be 0. If they are not 0 you do not see the scan result but a modified scan result.

There are many holes in my scan (like horizontal lines).

First note that it is not abnormal to have holes in a scan. The shape of the item you are scanning can make it impossible to scan it in one go. But if there are really missing horizontal lines you probably move the laser to quickly. Maybe you have a to high resolution set on your camera. If your camera is set to 1600 to 1200 you need at leasr 1200 frames to get all lines filled. With a framerate of 12/second that means your scan must take at least 100 seconds. Can you hold your laser and steadily turn it during 100 seconds so that you just passed the pattern? I can tell you I can not. For a 640 to 480 whith 30/second frame rate you can theoretically do a scan in 16 seconds.

When I scan and move my laser the depth picture changes.

This is caused by your calibration corners not being perfectly 90°. Note that it is considered a bad practice to move the laser during a scan.

Shapefusion can not put 2 scans together properly.

There are different reasons to get this situation

You do not have enough overlap

You should have a overlap of about 20% or more of the scanned surface. (At least 20% of mesh surface must be shared from adjacent scans, for a good aligning process).

Your scan quality is bad.

Basically any scan mistake can lead to this situation.

Symmetry or self-similarities

If your object has an axis of rotational/translational symmetry or if it has self-similarities, the computer might not find the right alignment.

beginner_mistakes.txt · Last modified: 2014/06/06 18:38 (external edit)