Impose a grid on an item for tracing.

The idea came to me, and I tried it. It works.
Useful when you need a .dxf of an odd-shaped item for routing, e- mailing etc. The grid is a diffuser for suspended ceiling fluorescent lighting fixtures. The grid spacing, in this case, is in mm and easily scaled.
This one was for a customer who wanted to use this sink because it fit her cabinet. It could be used for lots of things, I think.
http://i123.photobucket.com/albums/o290/Robatoy/Gridtrace.jpg
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Robatoy wrote:

Ooo! Clever.
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That's just a plain white grid diffuser? Not a bad idea. All I have around here are the parabolic reflector diffusors, which probably wouldn't work as well.
R
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It is a clear one, but I think a white one would work too.
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Right. Since you'd have to know the grid size and size the picture to make it work, wouldn't it be just as easy to take the picture, with a straight rule in frame, and then overlay an appropriately dimensioned grid in SketchUp, then export the DXF?
R
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On 5/30/2009 12:17 PM RicodJour spake thus:

Ackshooly, I could do that with my old copy of Corel Draw. Probably even with my lowly little Paint Shop Pro.
--
Found--the gene that causes belief in genetic determinism

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If you know how much barrel/pincushion distortion your camera lens creates, sure. That rule-in-the-picture trick, used since the daguerreotype days, is very limited in accuracy.
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Well, I guess that's true of any lens - you have to know it's limitations and compensate for them. You've taken a step in the right direction. You're in the jet age, but I think you need to join the space age: http://www.jvrb.org/archiv/1275/index_html?set_language=de&cl=de
http://www.spgdata3d.com/spg_yours_applications.php

Why? And put a number on "very limited". If it's a fixed focal length lens and you have two rulers, I don't see any real world difference in accuracy between the diffuser grid and the rulers. 'cept I usually have a couple rulers laying around and a ruler's line marking are easier to determine than a diffuser's edges.
R
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Ahh... TWO rules... that's better.
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I thought it was "And one ring to rule them." ;)
I still don't quite follow why you think a rule in a picture is inaccurate. Please elaborate.
R
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For openers, you'd have to be sure that the rule is perfectly planar to your imaging device, and that the second rule is coordinated with a known angle (usually 90-degrees), also planar to the imaging device. All of this is old hat, btw. http://www.etemplatesystem.com/Portals/37/etphoto%20brochure.pdf My little grid helper will be useful to some.
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Not exactly an insurmountable problem - I could probably scare up a square, use a newspaper or do any number of other things to get a 90. As far as the planar issue, how is that different than the diffuser? That's an issue with any photographic measurement technique.
A steel rule is less than 1/16" of an inch thick - for all intents flat. Not so with a diffuser. A diffuser has depth that won't help the situation. The center of your photograph with the diffuser will be normal to the lens, but the further from the center the bigger the distortion with a grid that has an appreciable thickness.

No doubt, I'm not arguing that. It's quick and more than reasonably effective for a down and dirty grid layout. I'll keep my eyes open for a diffuser getting tossed.
R
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This 2 x 4 foot diffuser was 8 bucks. HD, new.
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I'm never going to use it, so I don't want to pay for it. =:O
R
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