Hi everyone. This forum is really informative and you guys are doing some great work here! There is a department at my work that manages remote offices. They currently have many wooden boards on the wall which display various bits of information about the areas they are supposed to oversee. For years they have been talking about going digital and having touch screens replace all of these hanging boards. But it has never gone anywhere as the price of a large flat screen can be pricey. Exspecially as there are about 14 different hanging boards! So I am really excited about implementing a home made touch screen solution.

Anyhow, getting to the point, the first multi-touch screen I want to construct is a central table in the office which will display maps etc (Google earth etc). This will be later linked with the hanging boards via software. Problem is, it needs to be a medium size conference table that people can sit at. I am trying to find out what the best method is to get the largest screen size and still be a workable table. I can’t use a plain box shape as I need leg room. I can’t have the table so high off the ground that you can’t sit at it. The ideal screen size is about 6 feet wide and 3 1/2 feet tall (or whatever the closest standard size is to this). If anyone can direct me to the best way to go about this that would be appreciated. I assume I will definetly need to use mirrors to increase the projected image. But I don’t know all the ends and outs about this. The more mirrors I use the shorter the distance from the table top to projector etc? Thanks for any input you may have on this.

for that size you need something similar to a 70 inch tv. 

i think you can imitate what dlp tvs do if you have te budget, you can get a nice projector and some custom made mirrors. 

i post 2 approaches here, i suggest the first one, since no concave mirror is used, and you can still get a very slim device, you have to consider, when you have so short distance between the bottom of the box and the screen you’ll probably have to use multiple cameras also FTIR its not very likely to work on a 70 inch acrylic.

im not an expert but i think DI and 2-4 cameras plus a custom box will do the job.

Thanks for the fast reply and diagram lolec. If I understand your diagram correctly, the approxamite lengths are 18 inches deep and 58 inches long? (traditional method) Thats not too bad. In your traditional method diagram, the projector beam somehow gets projected on a right angle. How does that work?

I am aiming to replace an existing conference table with an DI multi touch. I want the table top itself to be the mulit touch surface so I will use a large peice of frosted glass.

You mentioned additional cameras. I assume you are refering to the IR cameras? Why would I need additional cameras. Could I not also point the camera to the glass the projector is using? Bit clueless on this so sorry if this is stupid.

Now that I am thinking about it, do you know if running two projectors (spliting the image in half) is workable. Meaning 1 projector only needs to cover half the distance and the other projecter covers the 2nd half. Therefore reducing the projector throw? Not sure if this has been done before. Seems like it would be messy and probably not worth it.

Thanks for your time.

newguy,

There is a technique built into VVVV called “boygrouping”, which allows you to easily divide up an image amongst multiple “screens” (in your case, the multiple projectors). I’m not sure what programming language you were planning on using for your project, but that might be one avenue to look into.

On a side note, I’ve been thinking about this problem myself a bit lately as well. I’m planning to use Flash/AS3 to write my programs, but then considered using the Flash renderer in V4 and boygrouping to divide the image up amongst multiple projectors. Not sure how well this would work, though.

well, to get the image projected on a right angle you have to calculate the inclination of the mirrir, the secret is that every bean have to travel the same distance between the projector and the screen.

yes , you can place the camera beside the projector, im not shure about the acuracy tough because projectors and cameras use diferent kind of lenses. I dont think its to difficult to solve… but, if you use 2 projectors you will definitely need 2 cameras.

the simplest solution i can think of, is to use a dual-output graphic card, you can connect 2 monitors and extend the desktop, its very simple ( windows will extend the desktop in a basic way, you can also use a multi monitor software like MultiMon to get advanced features)

To get an app working full screen you just have to maximize the window to use both screens.

i know for sure that nVidia cards have an option to flip the screen any way around, by flipping it 90° you’ll get what you need.
Actually im thinking on building a similar setup myself.

Good luck.

Wow! Thanks lolec. Your digrams are really helpfull.  I will probably take your suggested approach as I could build one part of the table and make sure I have it right and then duplicate it. That way I wont be locked into purchasing everything before I know it will work. Yes I am familiar with running the desktop on two screens and this is a good idea. Nice and simple. Will let you know how this goes.

Another question. I really dont have much experience with projectors, but is it possible to have projectors cross and still work? I just had another idea on reducing my projector throw but not sure it would work as it would mean the two projector beams cross. Let me know what you think.

rileydutton
Thanks for the tip on “boygrouping”. Will check this out as an option.

Could this method be used to create a massive screen such as 8ft x3ft? I am looking at create a large MT wall that is as thin as possible. Also which MT technology would be the best approach FTIR or DI for such a size screen?

Thanks everyone.

Yes, crossing projectors does work. The photons that are light are so small would need so many projectors all crossing beams to make any sort of collisions that it would be almost impossible.

mindspinguy - 30 October 2008 12:20 PM

Could this method be used to create a massive screen such as 8ft x3ft? I am looking at create a large MT wall that is as thin as possible. Also which MT technology would be the best approach FTIR or DI for such a size screen?

Thanks everyone.

hey mindspinguy
LLP (laser light plane) seems to be popular for ‘walls’...no reason why FTIR/DI wouldn’t work though. I haven’t built one myself, that’s just the impression I got from browsing the showcase category.

For something that big, I would put the projector in front of the wall rather than behind it to minimize thickness and avoiding mirrors, etc., but that would cast a shadow.

good luck
rbedi100

lolec - 16 May 2008 12:54 AM

for that size you need something similar to a 70 inch tv. 

i think you can imitate what dlp tvs do if you have te budget, you can get a nice projector and some custom made mirrors. 

Why imitate? Just buy old rear projection tv, install camera and change projector. Or if you have money to burn, buy newer hd model.
This would be a sweet hull for such a project http://www.retrothing.com/2008/08/general-electri.html