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Building of a large calibration panel.

Problems, solutions and discussion about scanning with a video projector and stripe patterns.

Building of a large calibration panel.

Postby as.sun » Wed Feb 10, 2016 2:53 pm

Hi,
We recently bought DAVID SLS-2. Now we have to scan very large object (front bumper of the car) with a margin of error no more than 5 mm. We did different tests with the scanner and we read a lot in the forum, and we came to the conclusion that we have to build a large calibration panel (1200/1680 mm). I started designing it and I came to a few questions on which I can not find an answer:
1. How accurate must be the angle between two panels? I noticed that the original panel has a clearance and this angle can be changed a little.
2. The distance from the plane on the right panel to the first point of the left panel does it matter (dimension "A")?
3. Should dimension "A" to be equal to the dimension "B"?
4. With camera and projector which are in the package SLS-2 is it possible to use such a large calibration panel?

Best Regards,
Peter Arakchiiski
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Re: Building of a large calibration panel.

Postby micr0 » Wed Feb 10, 2016 4:11 pm

SLS-2 should be able to scan a bumper. You may have to do it in a dark room as the projector doesn't emit that much light. You can also calibrate to a smaller work area and scan the bumper in sections.

The angle between the panels should be as close to 90°as possible. The inner column of dots should be half the distance to the corner as it is to the second column of dots (ideally). The way I understand it, David does compensate for this being slightly off and there being skew between the two panels but I tend to think that very accurate calibration is the first step to good scans, so I try to make my panels as close to perfect as possible. Flatness in the panels is also important.

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Re: Building of a large calibration panel.

Postby VDX » Wed Feb 10, 2016 4:38 pm

... a laser line can be much brighter than the beamer, if ambient light is an issue ...

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Re: Building of a large calibration panel.

Postby drndadoo » Thu Feb 11, 2016 10:08 am

Hi as.sun,

1. How accurate must be the angle between two panels? I noticed that the original panel has a clearance and this angle can be changed a little.
Exactly 90 degrees, if angle is changed your scans will be distorted. This two panels are X and Z axis of your coordination system.
Calibration can not compansate angle value.

2. The distance from the plane on the right panel to the first point of the left panel does it matter (dimension "A")?
3. Should dimension "A" to be equal to the dimension "B"?
I do not know the distance between this points but if the angle between your panels from top to bottom is indeed 90 degrees
then DAVID will compensate some minor errors with the calibration (for example if your black points on the right side are 1mm higher or lower then on the left side or dimension A is 1 mm bigger then dimension B...)
Dot dimensions should be accurate. You are not allowed to tilt the panels or the calibration pattern.

4. With camera and projector which are in the package SLS-2 is it possible to use such a large calibration panel?
Your only limitation is 500 ANSI-Lumen of K132+ projector. If the projector can display sharp and visible pattern then you are ready to go!
You can make scans in the garage so that patterns are more visible.

Micro´s explanation is really good and I would say once more that flatness of the panel is very important.
I have calibration pattern in vector format, you can just resize it to fit your needs. If you need this you can message me.
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Re: Building of a large calibration panel.

Postby as.sun » Fri Feb 12, 2016 9:23 am

Hi,
Thank you for your answers.
After discussing we decided to produce the calibration panel.
I still wonder whether to be a glass (6 mm) or polycarbonate (10 mm).
Panel will open only 90 °. I still wonder whether it is worth to do а print and on the other side with smaller calibration distances.
The panel should look like this.

Best Regards,
Peter Arakchiiski
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Re: Building of a large calibration panel.

Postby drndadoo » Fri Feb 12, 2016 1:21 pm

Looking nice. If you don´t have to travel a lot with your calibration panels then polycarbonate should be good, otherwise they could react on temperature and slightly bend.
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Re: Building of a large calibration panel.

Postby WalterMo » Fri Feb 12, 2016 1:50 pm

Hi,

I wouldn't use glass or plastic plates for such a big corner. Glass is rather heavy (30kg each wall) and sensitive to be damaged.
Big plastic plates will be protuberant if they are not stabilised by a sufficiently close framework.
Better are, in my opinion, plates of chipboard which have tubes inside or a honeycomb structure. Inner doors are made in this manner. They are relative light but also dimensionally stable.

Please also have a look to these threads:
viewtopic.php?f=1&t=1789

viewtopic.php?f=1&t=5897

Walter
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