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DAVID-Laserscanner Forum • View topic - Calib-Panels Adventure
Dear DAVID Community,

As you are probably aware, the entire DAVID company, team and product range has been integrated into HP Inc.
This forum is now read-only. Relevant content has been migrated to HP and merged into HP's Support Forums on November 1, 2016.

To start new discussions for 3D Scanning, please register and post your new topic at the HP Support Forums

Calib-Panels Adventure

The place for questions, problems, comments and tips regarding the camera calibration.

Calib-Panels Adventure

Postby hal » Wed Feb 20, 2008 10:59 pm

Hello to all Scanners,

Once upon a time...
They were two good and ingenious men, with a big and generous heart: Simon and Sven.
They created a machine of wonders, a "Wunderkammer", and gave it the name of DAVID.
This miracle of the science enchanted many people: we, the followers, faithful to the Holy Laser Line (someone loved the Red, others loved the Green).
But we didn't know that we fell in a whirl of pain and beauty, at the same time.
We must conquer the power of holy DAVID, with three divine items:

- the Camera, eye of power;
- the Laser, light of Saint Sven and Saint Simon;

and the most important, the sword of justice:

- the Calibration Panels.

This "epic" words are a joke, obviously. But the problem is real: Calibration Panels is a serious problem: the accuracy of the entire workflow depends on them.
I ask you one thing: You have the perfect calibration angle? The most precise? The most handy? The most versatile?
Ok, I'm not talking to you, MagWeb, you are the best :wink: .
But for the others, like me, the problem is real. MagWeb's system is the best, but not for all (dimension, weight,, handiness, transportablity,...).
If we need a secure, lightweight, transportable and easy to use Calibration Panels, at the same time PRECISE, how can we do?

At present day we talked about markers and how to use them, but not much about the real calibration corner, panels and system construction.

I think this forum's chapter can be a "container" for all solutions, all ideas and suggestions about how to build a good Calibration Panels system: structure, measures, materials, costs, ... .

A good test, for checking your calib-corner's precision, is the MagWeb's test: scan your background panels with "background_filter_factor" value at -1 (in "config" file, into david' main folder). If the planar meshes concide with the virtual grid, you are OK. In addition, you can scan it with laser-line from the top and from the bottom: check the results and compare the meshes. Or: scan a simple object in different positions in relation to the panels (near to them and far from them), one time with laser at the bottom, one time from the top. Compare the meshes.
If they coincide, you are good scanners, if they don't coincide, Simon and Sven cry :cry: .

I hope that this topic interests. Bye, Mattia.
Last edited by hal on Thu Feb 21, 2008 11:44 am, edited 11 times in total.
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poezis

Postby humanticnc » Wed Feb 20, 2008 11:31 pm

HI Hal

You were very poetic, the calibrating panel the most important. It brought it to me biggest improvement , that I prepared it punctual . I ask a man writing well to make a description from the production. For the unbroken development
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Postby Bongobat » Thu Feb 21, 2008 9:23 am

David Laserscanner the movie... with hal as obiwan kenobi and magweb as the wise yoda :lol: coming to a theater near you in 3d of course.

You must have read my mind Mattia I was just thinking we need a good discussion on corner construction. So my question for everyone is what material to make it out of? What material would be the best? My initial guess would be glass ground to precision and painted. Drawbacks is that it would be breakable and heavy and besides I dont think we need that much precision. So what about expanded polystyrene (EPS)? I think this would be the lightest and looks like it can be molded to be very straight. I would like something around 10 cm thick so you could stack them to build a bigger corner but stowed away for portability. Anyone try this or will I have to be the first? Where are thick sheets available? I have plenty of stuff like this http://en.wikipedia.org/wiki/Image:Styrofoam.jpg If only you could ground it up and remold it :evil:
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Postby humanticnc » Thu Feb 21, 2008 9:41 am

Hi Al

http://www.woodweb.com/knowledge_base/H ... n_MDF.html
I use this , but he is for me working my machine with what I cut it to fit a size
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Postby leo » Thu Feb 21, 2008 10:17 am

I got the best results with particleboard coated with melamine foil on both sides. These can be bought in many shops quite cheap(Wardrobe shelves ). I tried glass to and it is that direction I will go. I think glass is the best solution. Glass must be better for keeping the form. Particleboard can deform with time ?

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Postby Cmcandre » Thu Feb 21, 2008 5:48 pm

I plan on building a corner that can hold multiple sizes of calibration panels (mentioned by Bongobat's) such that say a 200mm corner can be slid in front of a 30mm corner but the same 90 precision can be kept in both. If you put the panels on rails you can also take advantage of the "4scanSetup" mentioned at http://www.david-laserscanner.com/forum ... =scan+flat
. All that would be needed is to make a stop or lock for the panel on a rail at a point that is measured then save the calibration file for that measurements. This would allow for easy scanning of flat surfaces (if they can be moved into position) or longer objects, like a baseball bat.

Also, has anyone else elevated their corner. After seeing the "use a mirror to get the laser to hit the underside of the object" I realized that setting my calibration corner on a desk limited me. Instead I've mounted it over anything and set up camera on a stool/table that is across a gap. This way I can manually paint the laser from both above and below the camera at enough of an angle to allow david to read it. Painting more in a single scan helps make meshing a lot easier as well.

Also does the flat surface make that much of a difference? If so at what point is it not flat enough. David ignores points close (within 20%?) to the corner so it seems that you really only need the corner to be ultra flat at the edges, where David looks to determine the laser plane. I ask because of the virtual corner mentioned in the forums which is ideal for using with a projector/"beamer" (yes I know what beamer means in Germany thanks to this forum) onto a wall. However a lot of walls have some sort of texture, if you could just place something flat at the edges of the camera's view would it matter what the texture in the middle was?

I have been using plain white posterboard. The cal sheet was affixed with a spray adhesive and a roller to eliminate bubbles and other defects but I know the posterboard is not perfect. I've taped the poster board together to hold it (like in the help) but I also have the back of the posterboard adhered to a wood corner to make sure that any small shakes won't knock it out of place, because sometimes I lean objects against the corner while scanning. I would think glass would not be the best idea as it's liquid properties would ruin the perfect 90 deg setup over time. This may not be noticeable, or even be present, but if you are spending a lot of time getting the precision of the corner right it may be something to consider.

Great topice, by the way
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Postby MagWeb » Thu Feb 21, 2008 8:06 pm

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Jedi course : starter lesson

Postby PZsolt » Fri Feb 22, 2008 12:27 am

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...

Postby hal » Fri Feb 22, 2008 12:39 am

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Postby MagWeb » Fri Feb 22, 2008 9:09 am

As the first red beam hit my green face today I remembered my name: Yoda

And I remembered MattiasT.

So I´m proud to present: YodasY

+++ simple to build for there are only right angles (the cam axle is optional)
+++ doesn´t hit the space were the object is to be placed

--- might collide with flat surfaces

@Obi Hal Kenobi:
Don´t the transparent panels lead to some scattering effect on the planes? An other way would be Bongobat's idea of magnetic foil / paint or separat patternboards.


May your laser shine bright today!

Yoda
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Re: ...

Postby humanticnc » Fri Feb 22, 2008 9:46 am

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Postby Bongobat » Fri Feb 22, 2008 1:25 pm

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Magweb's Yoda
(30.36 KiB) Downloaded 699 times
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Postby MagWeb » Fri Feb 22, 2008 8:48 pm

Hi,

for Greg fears problems with George I switched the film to X-men.

The Y mutates to X and solves the problem of surfacescanning.

But now I have a problem:
Who am I if I´m not Yoda any more?

Found a interesting light material for the planes: DIBOND this sandwichboard (aluminium and polyethylene) promisses " low weight, perfect flatness, high rigidity and weather-resistance"


Hm, who am I....

Edit: YtoXX makes negative scanning possible too
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Postby MagWeb » Sat Feb 23, 2008 10:15 am

Hi,

such system clamps would be usefull too:



nice day
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a good way

Postby hal » Tue Sep 23, 2008 12:42 pm

Hello,

Time ago, I've posted here my old David setup. Now is time to update the documentation about calibration panels system.

My actually structure works well with different size objects (I know that it isn't perfect, but I have a good results with it, and is quite light and moveable).

As you can see in the first image [1], it can be dismantled (and easily carry on a schoolbag and/or in a big bag) and assembled with three screws in few minutes.

With a second panels system (two thiny panels that you can open as a book) I can calibrate the camera (markers sheets are printed with a standard pc printer) [2]. The high and the distance between camera and panels is adjustable.

After removing the "book" of calibration, I can start with the scanning process, using the standard closed system [3] or the open windowed setup [4]. The laser can be moved freely.

In the second image you can see a typical David workflow: calibration with modified markers, scan pass from top and from down, depth image (as you can see from the little gap of colours gradient, in the top of the scan, that my structure is not so precise). Finally a grab image for texture and two final meshes, without and with texture (I have a b/w camera, sorry).

Hoping that my little experience can help someone, best regards,

Mattia

:!: A big thank to my friend Roberto "ARM", from CNC Italia Forum, that have cutted and milled the wood pieces of my structure. :wink:
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A kit like an IKEA article ;)
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Example with a toy gun 6 cm tall.
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