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Linearity after keystone adjustment


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I'm a newbie using 5.1 and have some experience with aligning projectors. Problem is, we need always to mount the projector so that it is on the outside top of a truss cube projecting inside on the floor http://www.eventworks.ae/page7/files/page7-1003-full.html

This gives you a lot keystone distortion. I now tried to adjust the keystone distortion with the grid using perspective and that works ok, but you end up first with a big linearity mismatch top to bottom of the picture, and, when you adjust that by getting the bottom part of the grid up you get rid of the linearity problem but the picture is half the size in y only.

I know you can do this with a projector like Christie with the Twistboard and resize the picture then, but not all projectors can do so.


Any suggestions?


Also one more question - to do linearity with the full adjustable grid is really difficult and eats a lot of time. Is there any way to move a complete single horizontal line up or down and is there any "undo" for the last action?

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  • 10 months later...

Bit late to help Xida, but others may benefit from an answer to this question.


To adjust linearity in the Geometry grid, use the 'mirror adjustments' check box to the right of the numerical value of the adjustment - see page 162 in the version 5 user guide. It's not much good if you need to use the full grid, but quite helpful otherwise.


If you're working with an off-axis projector on a flat surface, then stick with Perspective, Horizontal, or Vertical geometry, it will be a lot quicker, and should give you enough points. If your projection surface is complex, then you'll need to use a Full grid, and probably need to do a lot more than linearity.


As far as "undo" goes, it would be helpful, but no, it doesn't exist. A workaround you can use is to save (ok) the geometry window once you have it roughly the right shape, and on complex warps save each time you get one section right. That way if you do stuff it up, you can go back to the last time you saved.


Hope this helps

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Just a recommendation. Do not use more points if you do not need it. This is a linearity problem no need for more points.


But I think Dean recommendation is very good. Take the outerpart first, then the center part ( this is probably the one that you are missing).  then it should be ok, if you need to move the internal parts then use the next lever ( what I call parallels ).


It works, I can tell. :) good luck.



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