Hey all.

I was reading and watching a bunch of things about multitouch to prepare for my LLP build. I’ve read in the past that you cannot use fiducials with FTIR. But I thought of a way where maybe someone could get it to work. I know fiducials are just patterns underneath the object being tracked. I assume it is just an image that the camera recognizes. I understand that normal fiducials on a FTIR setup would just show up as a huge blob with no recognizable patterns.

But what if someone made the fiducials on the FTIR setup with raised silicone or rubber? Just print out the fiducial as normal, then take a tube of the ever popular Silicone I used for compliant surfaces and trace the fiducial till you get, perhaps a 5mm - 1 cm high fiducial. Then, only the part the camera is supposed to recognize with be touching the surface and only that area will be frustrated.

Has anyone toyed with this at all?

Thoughts?

The reason why traditional fiducials dont really work on a FTIR setup is that they require a force to the touch surface for them to make a contact and create the pattern.  And if the force isnt even then the pattern wont register.  The way to get around this is to make the pattern on the bottom, but have the fiducial itself be the emitter of IR light, so that the object shines down to the camera when placed on the surface.

i’ve thought about this a lot in the past month.

ir emitting fiducials contain the inherent drawback of requiring power, meaning they have to be electrical objects, which drives up their cost.

a weighted block with an etched silicone surface, however, seems reasonable to me… i think the issue is coming up with a silicone compound that changes the refractive index enough without the human touch on top of it (like is required for the compliant surface)

someone over on the monome forums also brought up the added friction and tangibility issues that a silicone protrusion imparts, but i think it’d be worth the drawback for less reactable-like applications.

It seems to me that it doesn’t even necessarily need to be silicone. Just something that’s etched and weighted that only makes contact with the compliant surface at certain points. Even those small felt furniture gliders you can get at hardware shops to make you furniture glide on carpet would probably work.

I’ve seen Tinkerman’s work with compliant surfaces and he rolled a battery across it. You could see the battery as a blob throughout the whole process. That means that it’s not necessary for the human touch. The fiducial would just need to be heavy enough. And when you change the material from silicone to felt, you eliminate the friction issues.

I really don’t think the fiducial needs to have a refractive index at all since the compliant surface is between the fiducial and the acrylic. It just needs enough weight to frustrate the surface of the acrylic.

I’m building a LLP setup myself, so I’ll need to play around with other ideas to make fiducials work for my purposes. Perhaps a powered fiducial is the only thing that will work for LLP. If anyone has ideas for a LLP compatible fiducial, let me know

im new to all this and not sure if this has already been discussed. But would simply making the fiducial out of a reflective material ie foil. work at all? just a thought

hei, welcome
no, reflective material won´t work for ftir. have a look at the wiki book to understand the different principles…

a silicone pattern would work on setups that don’t have a diffuser (i.e. lcd) and just have acrylic with our without a compliant surface. When the silicone touches the surface then the ligth frustrates into it. It then strikes the object it is glued to, reflecting the light down. In that way a fiducial would work, but only for LCD setups not projector screens which require a diffuser and work by the touch pressure coupling the textured silicone with the acrylic.