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DAVID-Laserscanner Forum • View topic - FULL SIZE car scanning
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

FULL SIZE car scanning

Questions, problems, comments and tips regarding the 3d scanning process.

Re: FULL SIZE car scanning

Postby Bongobat » Thu Mar 18, 2010 6:35 pm

Hi Dave,

Im not ignoring you. Looking over your previous post it seemes you asked and answered your own questions. I thought the last one was rhetorical and not directed to anyone in particular. You say you do not like to be publicly told you are wrong. Should I PM you? Should I not say anything? How can anyone debate you? Oh, I think you want me to agree with everything you say. The moon is full.

I hope you understand I was only trying to help you. I have looked back and think my original explination was quite adequate:
viewtopic.php?f=2&t=1750#p11056

I also think it was quite clear how I was using the term resolution. The same way the David Shop uses it for your camera's specs. The same way we have refered to it on these forums many times.

Yes, as far as I am concerned the scanning resolution will be the same for a salt shaker or a space shuttle. You scanned both at the same resolution.

Shoud we change our use of the term resolution to include something like a DPi (dots per document inch) or some theorectical DPI that relates depth map pixels to the object being scanned (dot per inch of the physical object). Or perhaps it is not a scanning resolution but a mesh density you want to define. Do you want to define this for clarity and usefullness or so you can say you were right?

I tried to the best of my ability to remedy your misconception about scanning and possilbly lead you to a better understanding of why you were having difficulties manipulating your files. I really want to see you succeed with your mission but cannot help you if you can not ever be told you are wrong. Perhaps someone with more patience can help.

Best of luck,

Greg
DealExtreme red line laser, Microsoft Lifecam HD-5000
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Re: FULL SIZE car scanning

Postby cnc Dave » Thu Mar 18, 2010 8:13 pm

Thanks Greg.
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Re: FULL SIZE car scanning

Postby Bugzuki » Thu Mar 18, 2010 8:47 pm

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Re: FULL SIZE car scanning

Postby MagWeb » Thu Mar 18, 2010 9:35 pm

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Re: FULL SIZE car scanning

Postby cnc Dave » Fri Mar 19, 2010 7:30 pm

Hey Paul,

If you need any further info. on car scanning, I'd be pleased to help.

Regards Dave
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Re: FULL SIZE car scanning

Postby Bugzuki » Fri Mar 19, 2010 9:30 pm

I will probably need more information after I get a small scanner made up. Did you have to calibrate the camera every time you moved to a different section.

I am still at the learning stage of trying to figure out where to get the calibration sheets and what the calibration data file is. I would love to buy a starter kit, but don't have the extra 600 bucks. Hopefully I will be able to justify the system soon and save up to get the professional version of the software to do the high resolution scanning.

What CAD package are you using to create the ground effects kit? Are you planning on cutting molds then forming the skirts with fiberglass, carbon or plastic, or are you planning to put the components on that you CNCed? If it were me I would probably try to make molds and then make lighter weight skirts.

Really cool model so far though.
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Re: FULL SIZE car scanning

Postby cnc Dave » Sat Mar 20, 2010 2:03 pm

Hi Paul,

So you’re wanting to make a kit too?

I built myself a polyurethane injection moulding machine. Eventually I would like to be able to scan the car, create the kit in RhinoCAD, CNC machine a closed mold in dense model board and go straight to injection moulding the parts. For my first run I intend to create the parts in RhinoCAD, then machine them from 'cheap' polystyrene. Then take a quick mould in fibreglass and produce a fibreglass part that I can fit to the car and fettle to fit perfectly. Then make a closed mould and injection mould them.

RhinoCad is one of the best for working with surfaces in a free form sort of way.

I had an almost 1 meter high calibration pattern printed on vinyl and stuck it to big glass sheets...

Image

I then set DAVID up for plane-less scanning and this way , you do not need to recalibrate each time, you simply move the camera and laser round the car and take scans.

The thing to remember though is that the bigger your calibration panel the less detail you will capture (less resolution).

Here’s an example of what I mean.

Image


Here the large object was scanned in one go, but because it was done with a large calibration panel, the low resolution did not give the required detail for the face.
So the face was scanned separately using a small calibration panel…

Image

The high resolution face was then added to the low resolution body to complete the image.

To the rest of the DAVID community that is apparently “distracting double talk” but I hope you understand.

You have to find a happy balance; because the more, big, high resolution scans you take and try to merge them together.. the slower DAVID gets and will eventually crash. I spent a long time playing with different size patterns …

Image
Image

But I found that the new calibration pattern at a scale of 586 gave the optimum resolution for the detail I needed….

Image

The above scan is produced from about 6 scans merged together. If they were high res 6 scans of a model car, DAVID could have fused them with ease, but because they were scans of a BIG object DAVID only just coped with merging them and it was a slow process even on a powerful computer.

To do the plane-less scanning you need a laser movement that will repeatedly make the same motion at the same speed every time. I spent a long time trying to do this with DC motor…

Image

and I got damn close to achieving it. I think if I had just added a rubber band to remove the backlash from the gear box, it might have done the job. But, because I only wanted to paint a Jaguar white once, I opted for the stepper motor and gearbox setup…
Image

Even here the rubber band to remove backlash in the gearbox is crucial.

To scan such a BIG object I used the best monochrome camera and most powerful 16Mwatt, red laser, as recommended by Sven. I’m happy with the results even if it’s left me a lot poorer :0) I see it as a good investment.

Hopefully, telling you my experience will save you all the time it’s taken me to get this right and ‘fast track’ you to your desired goal. I say this because of all the extremely generous people that have helped me.

And always remember “when the moon hits your eye like a big pizza pie……… that’s amoure! “


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Re: FULL SIZE car scanning

Postby MagWeb » Sat Mar 20, 2010 8:47 pm

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Re: FULL SIZE car scanning

Postby vw_bus » Sun Mar 21, 2010 2:38 am

Hello cnc Dave,
I'm new to DIY laser scanning, and have not got any of the equipment yet. However, your awsome Jag scans have motivated me to get much more keen to have a go at making my own backgroundless scanner. Thanks!

I was planning a stepper motor drive, but I read the history of your project, and noticed that you mentioned somewhere that in hindsight you think you you could have got your original DC motor driven laser actuator to work if you had taken the backlash out of it with a rubber band.
A stepper motor seems the 'right' way to go. However, a DC motor system based on one of the motors with a high ratio gearbox from mfacomodrills.com and an adjustable voltage regulator as a speed control would be so easy in comparison that it's tempting to try one first. If it doesn't work I may still be able to use the gearbox (or some of it's stages) with a stepper motor. I would be interested to know whether you think this would be worthwhile? Thanks,
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Postby hal » Sun Mar 21, 2010 3:20 am

Hello Dave,

again compliments for your great work of scanning, I take off my hat: as already I wrote, you are the first that try to scan a car :D .
But let me show, with an example, some suggestion how to encrease/solve your scan results and your scanning workflow.
I take a common object, like a straw hat (used for working in the vegetable garden of my house, under the implacable sun :wink: ).
It is not too small, not to big, I think usefull to show my "way" to scan an object, pieces after pieces, but without have a crash during the fusion process.

First of all, I'd took 24 scans all around the hat (it is light and deformable, so I must to scan it all around) using my camera + laser on a tripod, and without the panels, obviously (as you done for your car). After scanning, I've scans that count from 900k to 3.000k of triangles.

Image

David can easily manage they: I've aligned one after other, in pairs or combining a little group of them. At the end I've done a global alignment. This is the result.

Image

Well, now the big problem is (as you already know) how to fuse all these 24 big meshes without burning the CPU? :wink:
I've reduced (with David decimation tool) all the scans, and now they count from 75k to 250k triangles. The decimation tool reduce the mesh density but save the details, so I still have visible all the web of the blades of straw.
Now I can simply set the Poisson fusion value at an high resolution (I've chosen 1200) and wait the time that David play a tennis set with my CPU, and oplà, this is the result:

Image
Image
Image
Image
Image

Image

The final mesh count around 4.000k of triangles.
I think that, with the right strategy, you can scan the car pieces after pieces, using all your camera view and increase the "resolution" of your scans but without problems of pc crashes.
Hope this helps and I hope that you can see the tennis ball of the David/CPU match: http://www.youtube.com/watch?v=7tcaev66ed0

Best Regards,
Mattia
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Re: FULL SIZE car scanning

Postby cnc Dave » Sun Mar 21, 2010 12:57 pm

Hello VW-bug,

With the DC motor I did get pretty close, but for the odd random line. The trouble is that odd line throws out the dimensions of the object. That means you could no longer take accurate dimensions off the scan from one side of the line to the other side. It also makes a mess when you try to merge 2 scans, as one object is not the same as the other… it’s got a line thought it. You can see a line on my scan near the windows, this was caused because the upper part of the car was outside the area of the calibration pattern and DAVID starts to calculate the result.

When I first ran my stepper set up, I was horrified to see the scan still had lines… indeed they were worse than the scans with the DC motor! The rubber band solved the problem. I can only surmise that the rubber band would have cured the problem with the DC motor set up, but I’ve not tried it.

Regarding your question about converting mesh to a solid, I have been to 4 Solid Works seminars, 1 RhinoCAD seminar; I have posed the question to BobCAD, CNC forums, the David Forum, the Mach forum and many more. You always get the same half baked answer by someone who hasn’t grasped the point of your question :0)

The real answer is you will still need a top end program to do it. Mesh-to-Solid by sycode might do a small, low res object, but a thing the size of a car wing… no, not really. SolidWorks pro, say it can do it, but I have yet to see it done. I’ve seen people try. (professionals)



Regards Dave
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Re: FULL SIZE car scanning

Postby cnc Dave » Sun Mar 21, 2010 1:21 pm

Hello Gunter,

The correct answer to the resolution question is there is no answer...

In the same way as you can describe speed as Miles/hour, Km/hour, Meters/second...... you can use what ever ratio you like they are all correct. The only person that is wrong, is you, for telling me I am wrong.

I am saying "my van can only do 95 miles/hour."

You are saying "your wrong! it's km/hour and your driving on the wrong side of the road" :0)

Image

Image
I am saying " look at the low resolution sofa, scanned with a huge calibration panel compared to the high resolution fly, scanned with a small calibration pannel".

You are saying "each object has the same number of pixels, therefore the resolution is the same, because the resolution of the camera was the same"

To me, your definition of resolution is useless.

Walter and Paul, say "you can scan a car with a large calibration panel, but if you want detail, you will have to recalibrate with a smaller calibration panel and get in close."

That's the truth of the matter.

Regards Dave
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Re: FULL SIZE car scanning

Postby cnc Dave » Sun Mar 21, 2010 1:56 pm

Ciao Mattia!

My learned friend, now that is an answer.

You have enlightened me about decimation.

When you merged your hat, do you think you could have manually merged them without a long wait for the tennis match?

When I tried to merge my scans and clicked a point on the first object, DAVID would have a game of tennis before it even acknowledged I had clicked. It played tennis every click.

When I tried a fine alignment, and clicked on one object to select it, well, DAVID would play tennis with my CPU with a beech ball!

If you like I will send you some of my scans so you can see for yourself.

I would be interested to see if my scans of the car slow DAVID down more than your hat… Experimenting with an open mind.

Cordiali saluti,
Dave
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Postby hal » Sun Mar 21, 2010 3:29 pm

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Re: FULL SIZE car scanning

Postby MagWeb » Sun Mar 21, 2010 4:16 pm

Mr. cncDave,

I´m not going to continue this discussion with you. You may think that I am wrong - wish you good luck on your further way.
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