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Projection mapping issues...question about viewpoint

vvvv beta question
#1

Hey all,

Haven’t used V4 in years and I’m glad to see a different kind of interface. I’m starting my own in house projection mapping project and I’m a little stuck. I’m not doing it all in V4 so maybe this isn’t the best place to ask, but there seem to be experts here that I can’t find in other places.

My model is just a fictional cityscape with 3 skyscrapers in it. I’m using a short throw projector that is about 2ft from the surface of the shapes.

I outlined the shapes in illustrator through the lens of the projector so I know exactly what everything looks like through the lens.

I brought all of that into cinema 4d and made a model of the model. It looks fine on the screen, but when it’s projected the perspective is off, unless I look from behind the projector.

My 3d skills aren’t the best so I’m trying to wrap my head around what I need to do to fix or adjust the perspective, coming from the 3d geometry how to project on 3d geometry article. There is the concept of the spectator camera and the projector camera that I don’t quite understand.

Do I render an output from C4d from the spectator’s viewpoint and then use the camera mapping technique to make it look correct from the projector’s perspective? It just seems like it wouldn’t line up correctly. Is there a limit to how far away the spectator could be…and how much depth I can fake?

Could someone just put that concept in other words for me…I think the language in the 3d geometry article is what is confusing me…I would appreciate it! I can add pictures

#2

Do you have a photo of Hardware setup?

#3

yes i do actually. I’m sure this crazy short throw is messing me up in some way:

http://blairneal.com/pics/testshots/IMG_007.jpg
http://blairneal.com/pics/testshots/IMG_7478.JPG
http://blairneal.com/pics/testshots/IMG_7479.JPG

#4

from this i guess its not a technical problem but this is how fake perspective tricks our perception

#5

Almost get the point you mean. There is nothing wrong with the program you written but some parameter for projector need to be corrected. Would you be able to send me the program? tomorrow i’m free, so i may able to help.

#6

I’m not around the computer that has that software/file set on it until monday. Again most of it isn’t in vvvv yet, its mostly trying to figure otu the question of viewpoint in cinema4d or any 3d software first…just trying to see if it’s my short throw projector that is messing up my angle of view idea or if there’s a proper way to retexture my 3d model with a viewpoint render from another camera or something

#7

helo potrzebie,

i am not sure if i understand your problem. the result on the pictures you posted look quite good. it seems as we are seeing through the windows inside of the buildings.

now i see that the perspective is not 100% perfect but i am not sure if you mean this as the problem. if so, did you make sure the camera you used in cinema4d has the same lense characteristics and position as your real projector?

if this is not the problem you meant i’d go with viktor2’s remark. of course your effect only looks correct from the position of the projector as that is the position you took the image from, right? that is what the how-to-project-on-3d-geometry article tries to explain.

you can though choose a different spectator view than the projectors position. if that is what you want you have to follow those instructions: how to project on 3d geometry#virtual camera039s perspective is different to real world projector position

i.e. in cinema4d you choose any perspective from which you want the effect to be viewed. then in vvvv you replicate that perspective and project the texture (created with cinema) onto your virtual-scene replica and then take a view on that scene from the virtual-replica of your shortthrow projector. it is indeed a bit tricky to get your head around as well is always the attempt to describe the theory…so i hope that helped a bit.

#8

I agreed with joreg “make sure the camera you used in cinema4d has the same lense characteristics and position as your real projector” since it needs a precise projector calibration. you may need to set the projector position in c4d else real world projector to match the position. a little offset in angle view point can potentially effect in spectator view.

#9

thanks for your help everyone, I really appreciate it…I’m getting a slightly better idea but it’s not quite there yet

below is another picture of where I actually want my spectator view to be. The above picture I provided is the only place it looks really ‘correct’ but I want to shift that ‘correctness’ over to this area instead.

joreg I think I follow what you’re saying, but I’m also trying to think of whether I could accomplish all of the rendering steps in cinema 4d. Would I render out the animation from that side view…then import that as a movie texture and do ‘camera mapping’ back onto my model from the camera that is at the projector’s perspective? I think re-mapping the texture doesnt make much sense to me, at least when i tried that approach, everything just looked skewed…i just felt like i was missing a step

thanks again

where i want the viewpoint to be:

http://blairneal.com/pics/testshots/IMG_0025size.jpg

#10

fcourse you can do both render-passes in c4d. only advantage in doing at least the 2nd pass in vvvv is that you’d be more flexible with the real projectors position and orientation.

if you do the second pass also in c4d you’d need to re-render your animation everytime you want to move/reorientate the real projector. if you do the second pass in vvvv you can change the real projectors position, adapt the virtual camera accordingly e voila.

again the steps involved are (in your words):

  • render pass one: render out the animation from that side view
  • then import that as a movie texture and do ‘camera mapping’ back onto my model

where ‘camera mapping’ would be actually a projection of the movie-texture from the point of the ‘side view’ back onto the model.

  • render pass two: render the scene from the point (and using a lens) corresponding to your real projector.

ai?

#11

thanks so much again…this is amazingly helpful…I’ll give that a shot now that I’m back in front of the equipment and I’ll keep my fingers crossed

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