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Author Topic: Post your Point Clouds Here!  (Read 23982 times)

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Re: Post your Point Clouds Here!
« Reply #20 on: July 16, 2008, 12:27:17 AM »
Hello Gaston,

> > Neither the camera nor the lens should be pointed straight down. The camera and the lens need
> > to be pointed 90 degrees apart.
> > I have chosen to have the laser 30 degrees CW from the Z axis and the camera 60
> >  degrees CCW from the Z axis.

> As the same setup is used both for calibration and measurement why 90 deg be so important?
> I see that the amplitude of the deviation would be maximized with 90 deg but as I understand
> it the results would not be more valid.

If you were using a pinhole camera the geometry would not matter.

However, when you use a conventional camera with a lens which is parallel to the detector,
the optimal layout is with the object also parallel to the lens and the detector.

With the object (i.e. the laser plane) at 45 degrees to the camera lens, the image of the laser plane will NOT be parallel to the lens and therefore will not be superimposed on the detector. That means that you cannot get the entire laser plane in focus. That will hurt your accuracy.

The smaller your field of view the more of a problem you will have if the laser plane is not parallel to the lens and detector planes. It is possible that the accuracy using a 70 degree FOV is so bad already that the angle the camera makes with the laser does not make much difference.

There is a way to point the laser straight down the Z axis and set the camera at an oblique angle smaller than 90 degrees but this requires that the detector be mounted separately from the lens so that the detector can be tilted at the appropriate angle in accordance with the Scheimpflug condition.

For more detail on the normal arrangement and the Scheimpflug arrangement please read some of my posts in other threads in the Video Probing forum.

Tom Hubin
thubin@earthlink.net
Re: Post your Point Clouds Here!
« Reply #21 on: July 16, 2008, 07:57:36 AM »
Hi Tom,
I see your point. Thank you for the explanation.

You have mentioned previously here:

>I see that the camera is shipped with a lens for 70 degree FOV. The lens is replaceable. I suspect that the thread is M12-0.5mm. If so, you can get lenses on ebay. Search for >M12* and lens* in title and description...or I can point you to some I have seen listed. I intend to get some of these M12-0.5mm threaded lenses from ebay but have not yet >done so.

My search on Ebay was not very productive so I think I could use some pointers here.
Thank you,
Gaston
Re: Post your Point Clouds Here!
« Reply #22 on: July 16, 2008, 02:53:29 PM »
Hello Gaston,

> > I see that the camera is shipped with a lens for 70 degree FOV. The lens is replaceable.
> > I suspect that the thread is M12-0.5mm. If so, you can get lenses on ebay.
> > Search for M12* and lens* in title and description...or I can point you to some I have seen listed.

> My search on Ebay was not very productive so I think I could use some pointers here.

Below is a link to an inexpensive assortment on ebay. This vendor has many M12-0.5mm thread lenses listed
on ebay and at his store. I have no affiliation with this vendor and have not purchased anything from him.

I would suggest that you choose the longer focal lengths since you probably already have the shortest one.
The longer focal lengths will give you a smaller FOV with greater magnification and detail.

http://cgi.ebay.com/Any-4-pcs-3-6-6-8-12-16mm-CCTV-board-Lens-set-dome_W0QQitemZ270255253150QQcmdZViewItem?hash=item270255253150&_trksid=p3286.m14.l1318

Tom Hubin
thubin@earthlink.net
Re: Post your Point Clouds Here!
« Reply #23 on: July 17, 2008, 01:57:19 PM »
Thanks Tom for the Ebay lens package reference,
I will look that up.
Right how I'm making a setup with 90deg (45-45) between camera and laserĀ  :)
Gaston
Re: Post your Point Clouds Here!
« Reply #24 on: July 24, 2008, 01:25:14 AM »
I was trashing some old pills and decided to try scanning bottles, caps and pills.

The closeup of the round pills shows impressed "I-2". I think these pills came from an Aleve bottle.

The closeup of the capsule shaped pill shows impressed "NUPRIN".

Text on the Nuprin bottle is readable because the camera exposure time was set so that the white areas produced a strong and usable signal while the dark areas produced a weak and unusable signal. The weak signals appear as gaps in the bottle's surface.

The video probe used has a PlaytStation 2 silver camera which has about 45 degree fov. The laser is 5mw, 5vdc red module from Aixiz directly (not ebay). USB cable provides power.

Attached are the point cloud TXT file and a GIF file of the Rhino screen showing the point cloud.

Tom Hubin
thubin@earthlink.net
Re: Post your Point Clouds Here!
« Reply #25 on: July 24, 2008, 01:48:18 AM »
Hi Tom

Nice to see how good your scans are getting.

I'm curious how we are going to get deeper profiles scanned. Can we step the Z down and take another slice then stitch the two meshes together  or is getting a wider FOV setup the better way to go.

Cheers.

Mark

Still slowly building my CNC
Re: Post your Point Clouds Here!
« Reply #26 on: July 24, 2008, 02:09:13 AM »
> Hi Tom
> Nice to see how good your scans are getting.

Thanx.

> I'm curious how we are going to get deeper profiles scanned. Can we step the
> Z down and take another slice then stitch the two meshes together or is getting
> a wider FOV setup the better way to go.

See my suggested volume scanning at http://www.machsupport.com/forum/index.php/topic,7084.msg46309.html#msg46309

Small FOV is preferred for any detail and for less distortion. Then as many overlapping passes as necessary to get the job done.

Art, or whoever is working on the 3d video probe plugin, needs to set that up to be user friendly. Otherwise, you have to do each pass separately then combine later with a spread sheet to get the offsets right.

Tom Hubin
thubin@earthlink.net
Re: Post your Point Clouds Here!
« Reply #27 on: August 12, 2008, 02:24:50 AM »
Hello,

Here is a scan of a Quarter. Done in two overlapping passes since a quarter is a little wider than the video probe FOV.

Video probe camera is a 3Com Watchport/V2 set for 640x480 resolution and using a 12mm focal length lens.

Video probe laser module by Aixiz is 5vdc, 5mw, 635nm, 39 degree line lens, unknown collimating lens focal length. Arrangement of camera and laser shown in several threads over the last few months.

Scaling is close but not quite right.

I deleted the base points in Rhino so as to make the details of Washington's head more apparent. However, the data set in the text file does include the base points. That is one of the reasons that the text file is so large.

Tom Hubin
thubin@earthlink.net
Re: Post your Point Clouds Here!
« Reply #28 on: August 21, 2008, 12:38:57 AM »
Here is a two pass scan of a dead cricket done with a 12mm focal length lens on a 3Com Watchport/V2 webcam.

Maybe I can find a Praying Mantis for a live scan.;)

Tom Hubin
thubin@earthlink.net
Re: Post your Point Clouds Here!
« Reply #29 on: August 21, 2008, 11:39:38 AM »
Hi Tom,
You are becoming the expert at scanning small object :) You are now ready to machine one of these beast :)
What's next?
Have you tried to translate your data to mm and do a mesh in Machcloud?
Gaston
« Last Edit: August 21, 2008, 11:41:47 AM by ggagnon »