Physical Sandbox Design Question

Home Forums AR Sandbox Forum Physical Sandbox Design Question

This topic contains 3 replies, has 3 voices, and was last updated by  Oliver Kreylos 6 months ago.

Viewing 4 posts - 1 through 4 (of 4 total)
  • Author
    Posts
  • #111024

    Aussie3d
    Participant

    THANKYOU
    I’ll start out by saying a big Thank you to all the people whom put this into the open source world, its a wonderful project and my inner nerd loves it (hopefully my kids will like it also)

    BACK GROUND
    My apologies if this is a basic or obvious question but I’m at the start of this build and perhaps it will help others whom follow

    As a home user I’m trying to recycle as many parts as possible from stuff I have laying around as such I have a Promethean PRM 35 projector which I think started life as an interactive white board, perhaps not the best unit but its what I have and I’m on a real tight budget for this build.

    The projector has a short throw, and seem to project above the physical level of the unit, this combined with its limited keystone tweak is causing trouble with the mounting of the projector.

    QUESTIONS
    1) How should the physical alignment of the projector area be with respect to the sandbox? Should it be aligned with the base area (my first assumption) or the top edge of the box?
    –If it aligns with the base level then their will be noticeable “blind spots” (in the upper perimeter) because of the short through of the projector refer to SKETCH
    –Where should the image be focused (top edge / bottom edge or average height)?

    2) Must the projected image fit the box precisely & align with the camera precisely or is this something that is calibrated later?
    –If calibrated can the image overflow the box a small amount? (eg just making things easier on the physical setup side)

    3) Because of the projector seems to project above its top edge the bottom edge projection line is on a rising gradient to the screen. This is causing a blank area where the projected image cannot hit the bottom of the sandbox (eg shadowing from the rear sanbox wall). Refer to photos and SKETCH.
    –Has anyone come across this before?
    –Does anyone have any ideas on how best to over come this? (yes a centreline projector would be lovely but on a budget please)
    –I was kicking around the idea of putting a blanking wedge of timber inside the sandbox (just to restrict the sand to the areas the projector can hit) but not sure on what the implications would be on program side of things

    Build Photos –> https://imgur.com/y14n20J https://imgur.com/rybeEXH https://imgur.com/I1UYghp
    Refer to sketch –> https://imgur.com/a/IH9Fi

    Any thought, ideas or comments would be appreciated.

    #111058

    MaxD
    Participant

    Hi,
    my alignement is to the base line and works well. Of course you have to tilt a bit the projector towards his base to avoid a blind region at the base of the sandbox.
    I prefere not to overflow the projected area, it will remain active also after calibration: extend the projected area exactly over the sand and focus on it.
    If you need drawings just tell me!

    #111084

    Aussie3d
    Participant

    Thanks MaxD for the reply,
    I’ve actually made a lot of progress from this post, and a lot of lessons learned along the way.

    I’ll post a few here for anyone whom follows:

    How should the physical alignment of the projector area be with respect to the sandbox? Should it be aligned with the base area (my first assumption) or the top edge of the box?
    –If it aligns with the base level then their will be noticeable “blind spots” (in the upper perimeter) because of the short through of the projector refer to SKETCH
    –Where should the image be focused (top edge / bottom edge or average height)?

    As far as I can tell the excepted wisdom is that projector alignment/focus is with the average sand level seems to be the accepted convention people are using, and the “blind spots” will occur if kids build up near the outer perimeter.
    The shorter the throw on the projector (or the lower the sand surface) the worse the blind spots seem to be.

    Must the projected image fit the box precisely & align with the camera precisely or is this something that is calibrated later?
    –If calibrated can the image overflow the box a small amount? (eg just making things easier on the physical setup side)

    I’m still not 100% on this one but looks like there is straight forward calibration between the Kinect and the projected image (as nicely outline in the setup instructions), this is then calibrated to the inner corners of the box, so whilst a little overflow is plausible but not ideal and most people are setting projectors to be aligned to the inside edges of the box at the average sand level.

    Because…the chosen bottom edge projection line is on a rising gradient to the screen. This is causing a blank area where the projected image cannot hit the bottom of the sandbox (eg shadowing from the rear sanbox wall). Refer to photos and SKETCH.
    –Has anyone come across this before?
    –Does anyone have any ideas on how best to over come this? (yes a centreline projector would be lovely but on a budget please)

    I think the answer seems to be this is not an ideal choice of projector.
    -If a projector has a raising baseline then it needs a large keystone effect to allow the bottom cord to be vertical above the back edge of the box eg tilt the projector under and square the image with the keystone.
    If selecting a project best go for one with a horizontal base line or better yet a centreline projector, in my case suck it up and live with a blind spot or perhaps add a wedge (not yet tested)

    Extra notes for the unwise.
    Looks like the Kinect V2 (is not yet supported) is very different from the Kinect V1 / Kinect 360 but fortunately these are really cheap ($5 second hand)

    Good luck and thanks for the response

    #111091

    Oliver Kreylos
    Moderator

    To your questions:

    1) You can align the projector however necessary to fill the box with light. It’s generally a bit better for focus if the projector is at a right angle to the box base / flat sand surface, as the focus plane will then be horizontal as well. But if you have a projector that projects too much above centerline, you can push it into the sandbox, and tilt it the other direction to avoid blind spots. Important: Do not use the projector’s built-in keystone correction controls. The projector calibration step at the end will do keystone correction for you. Built-in keystone correction degrades image quality.

    You should focus the projector on the average sand surface. That way it will be least blurry during use. If you have to tilt your projector, focus it so that the middle of the average sand surface is sharp.

    2) It doesn’t really matter how the projected image overlays the box, as long as it fills it sufficiently and doesn’t go too much over the sides (which may cause problems seeing the calibration disk). Projector calibration will take care of it. I just installed an AR Sandbox with a 16:10 projector over a 4:3 box, with the projected image hanging over the sides. It didn’t cause issues, since the image outside the box is all black and the overprojection is invisible.

    3) As I said above, it’s OK to push the projector in and tilt it backwards if you need to.

Viewing 4 posts - 1 through 4 (of 4 total)

You must be logged in to reply to this topic.

Comments are closed.