Making a Rear DI setup, blobs and fiducials: A list of the main problems and their solutions or advise …
Posted: 19 March 2011 04:11 PM   [ Ignore ]
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Hi all, sorry for my english.

After a lot of little and big issues I am finishing my setup.

It is a rear di, screen size 45 x 60 cm ( 29ยด). Height 85 cm (33 inch).
The purpose of this setup is to be able to do finger tracking AND fiducials, as a reactable setup.

I wanted to use the cheapest and the material I already had.
-common plexiglass ,
-tracing paper as surface projection on top of the plexiglass, and transparency sheet to protect the tracing paper.
-wood: MDF,
-Lots of screws and other stuff.
-Normal mirror,
-modified PS3 eye with 3 photo negatives on top to make visible filter.
-normal IR leds, visual angle 30 degrees , 920 nm, 2 groups of 16 leds.
-Macbook pro., OSX, snow leopard, macam driver. Reactivision, CCV.
-Benq normal DSP projector.

So, while doing this setup i faced LOT of different problems and found here so many advices, that I could solve almost all of them.
I think it would be a good help to others to make a list of the main issues for this kind of setup and to give the answers to them.

So these are a sumary of the issues I encontered:

-Positioning the mirror, projector and camera.
That was a big problem. Finally I am pointing the projector downwards and using the mirror to bounce upwards the light to the screen (keystone around 6).
So the projector must be at one side of the screen if you imagine that from the top, to not to block its own light. This makes the setup almost 20 cm larger in one side.
I had to do that because ALL the other solutions had a problem : The light coming from the reflexion from the plexiglas was going to the mirror, reflected, and was
visible in the projection, making strange artifacts. Anybody knows another position that avoids that?

The camera is pointing directly upwards, without almost any distorsion, which facilitates a lot the calibration with reactivision. As I am using the same lens mount after removing
the IR filter, I have only one focal distance, and 85 cm is the minimum height to see the full screen size.

As for the mirror, and camera, the most difficult part (and I did not reach a permanent solution) is to make a good and precise mount for the projector, that allows fine tunning and
is stable. I will post some pictures to show you my solution.  My projector is atached to one of the MDF sides.

Fine tunning the height of the corners of the mirror (as for the camera) is very important to be able to get precisely the projection we want. I will post pictures of that.

How did you do it? 

So, having good mounts for the mirror, camera and projector is really extremely useful, and helps a lot the calibration with reactivision (the grid we draw on paper can remain tha same, etc...)
Any ideas about that would be great.

The second big issue is the IR light.
Hot spots from the leds made impossible any solution except shadowing them (that is to cover a surface to avoid light from a led or its reflection to be seen by the camera)
(you can follow this thread to know more: http://nuigroup.com/forums/viewthread/11755/ )

Trying again and again, I found that for my setup, I was better to put the led stripes pointing with an angle of 45 degrees upwards to illuminate the opposite side from where they are set. They stay
at 40 cm from the bottom, and are set in the 45 cm (short ones) sides . I can move each led ( I let a portion of the led “legs” to be able to be moved) until I get an even illumination. It is working
great for fiducials recognition, and I get this good green dot on them that says the tracking is great. But it gets really difficult to have finger tracking with reactivision and this setup.
I know I have not enough IR light (only 32 normal IR leds) because I have to increase the gain to maximum, getting this unstable and grainy image.

Anybody could do blob and fiducials with this kind of setup?

I found a good think before getting the leds:
I can use normal bulb lights, and covering the light with photo negatives: visible light is blocked and IR is not, and it really works if the bulbs are not seen by the camera. But it gets too hot !.

The best way to avoid hotspots is to prevent reflections using a non reflective surface in the bottom of the plexiglass. But the problem is then that the image from the fiducials gets blurry and
it is not possible to track them.
there is perhaps as I read, a good surface that prevents reflections but does not blurr. That would be PERFECT!,
do you know which one could it be?

i will post some pictures tomorrow and detail some other aspects.

thank you !.

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Posted: 22 March 2011 03:04 PM   [ Ignore ]   [ # 1 ]
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In Multi-Touch Technologies Book (page 75 - Appendix C: Building a Rear-DI Setup), the author used a thick frosted glass (sand blasted) as projection surface. I am planning to use the same.

I am building a MT table using the 48 IR LED set from DealExtreme (I think it’s the same used by EfeNDy’s MT setup).

Waiting for your pics. Thank you for sharing your experiences. It’s great for beginners.

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Posted: 23 March 2011 03:51 AM   [ Ignore ]   [ # 2 ]
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Hi,

here are a few pictures I took with my phone.
It is the setup in its “draft” status. But the positions and mesurements and elements are the ones which work.
The setup is working great for fiducials and also for finger tracking in CCV 1.4 .
I will receive soon 200 IR leds from ebay:
(200 ir leds ebay UK )
and improve the illumination.

Here are the pictures attached.
Hope this help somebody.

To summarize the questions I still have that could solve issues:

- Is there a inti-reflective surface that is transparent to stick it under the acrilic to avoid hot spots, but still enabling fiducial recognition?
- Is there an easy method to make mounts for the mirror and camera (and projector) that is very precise and stable?
- Any body could do fiducial and blobs with reactivision in a mac?

Thanks !

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23032011.jpg23032011_001.jpg23032011_003.jpg23032011_002.jpg23032011_004.jpg23032011_006.jpg23032011_009.jpg23032011_007.jpg
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Posted: 23 March 2011 09:47 AM   [ Ignore ]   [ # 3 ]
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What’s the projector and camera model you’re using in this setup?

Have you tried ProLight Film as anti-reflective surface?

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Posted: 23 March 2011 11:23 AM   [ Ignore ]   [ # 4 ]
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Hi,

i am using a PS3 eye modified and the projector is a Benq MP622c .

No, i did not use ProLight surface . Do you mean to use it as a rear projection surface or only as an antireflective? Because i would need an anti reflective, but
transparent, to be able to track fiducials. I visited ProLight films , but i think they only have rear projection surfaces (and they are expensive), but they look great !

Check this other thread for more info about my setup:

http://nuigroup.com/forums/viewthread/12198/

thanks for the answer

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Posted: 24 March 2011 04:28 AM   [ Ignore ]   [ # 5 ]
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Hey, i am building a rear DI as well, basically i am using the same technique as yours, the projector downwards to a mirror, which reflects back on the screen without having that much of keystone. Im having the problem of what to use for the screen, i mean for example frosted glass? acrylic with a diffuser? Any help would be very appreciated. Thanks smile

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Posted: 24 March 2011 05:38 AM   [ Ignore ]   [ # 6 ]
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Hi,

I am using a normal drafting paper as diffuser, on top of the acrylic and a transparency sheet above the diffuser. It is not a definitive solution.
You can try Mylar, Vellum , Duralar drafting paper, vinyl Table cloth or shower curtain, etc.  as the cheaps ones.

Rosco Grey, And other projection surfaces are also good, (rosco grey is not so expensive) they say.

Also you can buy an acrylic that has one of the sides meant for projection.
Look at peau productions web site or this forum to know more.
Where do you live?

bye.

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Posted: 24 March 2011 09:04 AM   [ Ignore ]   [ # 7 ]
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I live in Brazil (Rio de Janeiro) and is very hard to find some materials used in MT setups.

The worst step for me is to find a good diffuser (like Mylar, Duralar, etc) in Brazil.

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Posted: 25 March 2011 12:17 PM   [ Ignore ]   [ # 8 ]
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Hey Miguel,

I live in Malta, at first i wanted to buy the Endlighten acrylic but they don’t sell it here. I was thinking about using a frosted glass or a layers from an LCD but i am afraid that the blobs will not show good :S im really confused.

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Posted: 02 April 2011 07:54 PM   [ Ignore ]   [ # 9 ]
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Hi,

having a normal acrylic and a diffuser-projection surface is ok, i think.
Diffuser can be tracing paper or special paper used by architects. It is very cheap, you can find it anywhere and it gives good results. Of course one could find a better one, as some rear projection surfaces that you can check in peauproductions website.
Some people are using frosted glass with good results.

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Posted: 22 September 2011 08:50 AM   [ Ignore ]   [ # 10 ]
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Hi,
I am building a similar installation with a circle shape table, ~70cm diameter.
I’ve also adopted reactivision which seems much more accurate for fiducials than ccv (and actually much more stable...).
I have a proper fiducial/fingers recognition when having the camera very, very close to the projection/touch surface (~40cm), though I will need to enlarge PSeye angle with a proper lens to cover the full screen (as did reactAble I guess since they’ve introduced an algo for flatten the image in calibration).
In your install, it seems from your photos that you’ve placed camera quite far from touch surface.
How did you manage to have proper fiducial recognition with it?
Thx!

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Posted: 22 September 2011 08:52 AM   [ Ignore ]   [ # 11 ]
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NUILeo - 22 September 2011 08:50 AM

Hi,
I am building a similar installation with a circle shape table, ~70cm diameter.
I’ve also adopted reactivision which seems much more accurate for fiducials than ccv (and actually much more stable...).
I have a proper fiducial/fingers recognition when having the camera very, very close to the projection/touch surface (~40cm, with fiducials ~6-7cm), though I will need to enlarge PSeye angle with a proper lens to cover the full screen (as did reactAble I guess since they’ve introduced an algo for flatten the image in calibration).
In your install, it seems from your photos that you’ve placed camera quite far from touch surface.
How did you manage to have proper fiducial recognition with it?
Thx!

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Posted: 22 September 2011 11:32 AM   [ Ignore ]   [ # 12 ]
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Hi NUILeo,

yes, the camera in our setup is aprox at 80cm from the surface.
We have now another setup, that you can check in
http://www.tangiblex.net

Still in this one the camera is at 80cm from the surface and the lens is the proper PS3eye lens or a 12mm one (i prefer the ps3eye lens). That makes the camera to see almost exactly the complete surface, and not more than that.
Check for sure that you have a focused image, turning the lens until you have it. We did not have any problem with that. Our fids are 6cm diameter and they are very stable with Reactivision.

I hope thiis helps.

miguel.

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Posted: 11 November 2011 05:12 PM   [ Ignore ]   [ # 13 ]
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Hi Miguel,

Could you please share your reactivision settings file, and your cam settings?

We’ve tried to improve detection adjusting lights, gradient, equalizer, changing fiducials and engine; but still we have a very poor fiducial detection if ze dont put the cam very close (though we have an install witch has more or less your’s dimensions).

I suspect there’s something wrong with our cam resolution -though it’s a classic PS3 eye...-, I attach you a snapshot for advice.
But clearly it seems quite buggy, since we can easilly recognize fiducials on screen, reactivision should…

Btw, did anyone try to compile ccv 1.5 for osx? Wanted to give it a try for fiducials, but I really doubt it will do better.

Seems the xcode project comes from a prehistoric version…
Think that moving this project to github and integrate its features to cool frameworks like movid seems like a good idea.
If not, I’m afraid that ccv will soon turn in one of those easilly forgotten windows shareware..

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Posted: 11 November 2011 07:18 PM   [ Ignore ]   [ # 14 ]
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Hi,

so, just check the most forgotten issue: the resolution in Reactivision or CCV of your camera. If you see 320x240, you wont be able to detect the fids.
Change in camera.xml or reactivision.xml the resolution to 640x480.
Make the same in CCV !
Hope this helps.

Why is your image inverted in white/black?  Fids should be white with black borders.... Print fids number 0 to 10 and check that.. Arre you inverting colors in CCV or Reactivision?
Are you trying with normal light? 
Seems also that you focus is not the best… And that you could approach a little bit more your camera....

miguel.
http://www.tangiblex.net

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