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2 laser scanning setups, what are the pros and cons?

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

2 laser scanning setups, what are the pros and cons?

Postby karlkohl » Sun Jan 16, 2011 8:40 am

Hello,
I have never done laser scanning before however after reading many posts on this forum and searching on the web I found some basic setups for 3d laser scanning.

lzr.png


I'm basically interested in 360deg full object scans.

In the first method.
The laser is either above or below the cam with the required intersection angle.
The laser sweeps top to bottom or vice versa and line is horizontal.
After one scan the object moves 45 deg and the process restarts till 360 deg is covered

In the second method
the laser is next to the cam with required intersection angle.
The laser is stationary and the object is continuously rotating till complete 360 deg scan is over.

I don't know specifics as I have never done laser scanning before.
However what I would like to know is does David support both these types of scanning?

I'm not sure I will get the whole object in just this one position possibly it would have to be turned and aligned into different positions to get the whole object.
How to capture the top and the bottom of the object.

Waiting for inputs from pros and experts!
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Re: 2 laser scanning setups, what are the pros and cons?

Postby MagWeb » Sun Jan 16, 2011 11:31 am

Hi,

David supports only the setup 1

The main advantage of setup 2 (fixed intersection angle+known motion) as used e.g in such a turntable-setup (one can use this idea in other ways too, as moving a laser-cam-combo linear or rotating it <<<see: download/file.php?id=1241&mode=view ) is, that you get a full 360° scan in one pass. But there are no chances to get data in special undercuts or cavities this way (e.g: the inner side between the handle of a teapot aqnd the pot will always be in shadow)

The way DAVID uses (grabbing different static aspects and mounting them finally) allows to capture surface data in holes much better. You also have the option to do some closer up scans on detailed regions and merge them...
And last but not least: This system basically needs the simplest hardware components.

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Re: 2 laser scanning setups, what are the pros and cons?

Postby karlkohl » Mon Jan 17, 2011 7:01 am

Hello Magweb,
Thanks for the additional setups of laser scanning?

So David can do use only setup 1 for now, that's good to hear and that's what I will work with.
My question is that for 360 deg scans would 45deg scans work? that would be 8 scans of the object and then I would need to scan the top and bottom regions of the object right?
Would this be the general idea of scanning 360deg.

Secondly how much time does each scan take or to get accurate scans, how slowly should the laser sweep across the model, are there any figures for this in general?
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Re: 2 laser scanning setups, what are the pros and cons?

Postby MagWeb » Mon Jan 17, 2011 12:59 pm

Hi,

8 should be good for a simple object. For a more complex one you will need some more....

Sometimes you can avoid the top- and bottomview scan if you scan 4 of your scans at an viewing angle (of a about45°) from above and 4 from below (alternating, always turned 45° around Y).

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Re: 2 laser scanning setups, what are the pros and cons?

Postby karlkohl » Mon Jan 17, 2011 5:46 pm

Thanks for the reply Magweb.
The 45 deg inclination for the object is a brilliant idea!

Regarding the speed of the laser, what should be the optimum speed of the motor that sweeps the laser?
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Re: 2 laser scanning setups, what are the pros and cons?

Postby MagWeb » Mon Jan 17, 2011 8:27 pm

Well,

if your object is and you are a patient one: The slower the better (there is some oversampling effect if a single pixel is calculated several times while the laserline has moved a little bit)

If you are not that kind of patient: The fastest way that captures data for each possible pixel means that you move your line one pixel further per captured frame. That means for a vertical res of 600 pixels at 15 frames per sec: 600 / 15 = 40 >>> about 40 sec to sweep you laser one time across the visible field of view.

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Re: 2 laser scanning setups, what are the pros and cons?

Postby karlkohl » Tue Jan 18, 2011 8:47 am

Many thanks Gunter!
These are extremely valuable suggestions!

I was wondering
1. Does the frame rate of the camera have any impact on the scanning quality, that is, does it mean, higher frame rate means better quality?
2. Would a monochrome camera produce better results in terms of quality of scanned data than a color camera?
3. If monochrome camera gives better quality then how do we get the textures in this case? Do we need a separate color camera to acquire textures?

Cheers!
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Re: 2 laser scanning setups, what are the pros and cons?

Postby eliscio » Tue Jan 18, 2011 12:20 pm

1. Higher frame rate means you can move the laser a bit faster and still capture a full scan without as many gaps or holes to fill. So, this helps get a better scan, but not from an accuracy standpoint.
2. A monochrome camera uses all the pixels to capture data and not just the red, blue or green sensors. As a result, you get a better scan when you compare to a color camera.
3. I haven't done this before, but if you search the forum, I think Gunter or MagWeb might have used filters and such to recombine into a color image. It's not so simple I think, but possible.

I think a lot of people (including myself) have asked questions about quality, but if you have a look at what can be done with just the basic David Starter Kit, I would say that it's suitable for 80% or more of the projects that are out there!

Cheers,

Eugene
www.ai2-3d.com
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Re: 2 laser scanning setups, what are the pros and cons?

Postby karlkohl » Wed Jan 19, 2011 6:29 am

Thanks Eugene for the fine answer.

When scanning with monochrome camera, I guess the color of the laser doesn't matter as the monochrome camera would not have a "bayer filter".
Possibly while using a color camera, a green laser would be more useful as the camera is more sensitive to green rather than red or blue.

I think a lot of people (including myself) have asked questions about quality, but if you have a look at what can be done with just the basic David Starter Kit, I would say that it's suitable for 80% or more of the projects that are out there!


Yes! you seem to be right, in hindsight it seems to me that if we dive head-on into a topic, the answers would come naturally!! :)

Hoping that Gunter would provide some insights on texture capture when scanning with a monochrome camera!

Cheers!
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Re: 2 laser scanning setups, what are the pros and cons?

Postby Oneinwhite » Wed Jan 19, 2011 11:22 am

Green lasers are better with regards to to accuracy being picked up by 50% of the camera sensor not 25% like red.

I was wondering what you plan to be scanning? If its for professional stuff the monochrome might make a difference but if accuracy doesn't have to be as accurate as possible you'll find a colour sensor (complemented with a stepper motor and accurate calibration corner) is hardly inaccurate. I do remember a thread about adding a texture to monochrome camera pictures but i couldn't find it in the search i fear!
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Re: 2 laser scanning setups, what are the pros and cons?

Postby eliscio » Wed Jan 19, 2011 1:43 pm

If you use a projected white line from a video projector, you get the combination of red, blue and green so you are in fact using all of the camera sensors. One other benefit of using the video projector is that you can use a set of lenses to reduce the size of the line, making it quite fine.
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Re: 2 laser scanning setups, what are the pros and cons?

Postby MagWeb » Wed Jan 19, 2011 5:55 pm

Hi

karlkohl wrote:Hoping that Gunter would provide some insights on texture capture when scanning with a monochrome camera!


Please look here:

viewtopic.php?f=6&t=691
viewtopic.php?f=3&t=1151

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