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I'm not entirely sure if this is the right place to ask this, so apologies in advance if it doesn't belong.

I have a curved surface with many small, irregular holes in it that I would like to measure. The surface is in a location that makes it awkward to work with, and is effectively immobile. Are there any technologies or techniques that could let me take a 1:1 imprint or copy that is more portable? Being able to 'flatten' the copy would be convenient but not required.

The surface is thin and the reverse is accessible (though again with some difficulty) if at all applicable.

Edit: Specifically, i'm trying to gauge the accuracy of another measuring process, so computer vision techniques are undesirable.

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  • $\begingroup$ what aspect of the curved surface are you wanting to measure? Displaced volume; width, height, depth? For the measurements you are seeking, what will be the reference point(s)? Is there a consistent reference surface/plane/edge from which you can base your measurements? Is there a photo or drawing available for easier determination of an answer? $\endgroup$ – fred_dot_u Mar 6 '18 at 21:00
  • $\begingroup$ I'm trying to measure the sizes of holes present in the surface, specifically area and length across. Reference points aren't strictly required, as long as each hole is accurate. $\endgroup$ – Kevin de Haan Mar 6 '18 at 21:38
  • $\begingroup$ Howabout laser scanning? $\endgroup$ – joojaa Mar 7 '18 at 9:05
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If the holes are small enough and you don't care about spacing measurements, you could use what are called pin gauges. These will obviously not work on non-circular holes (irregular?)

pin gauges

These are available in sets of various ranges. The precision is quite good, often measured in tenths of a thousandths of an inch.

If that is excessive in terms of precision and especially in terms of cost, there's a much less elaborate method you can consider.

I initially planned to suggest modeling clay, but it has limits with respect to handling. You would flatten a sheet of the stuff and press it against the surface with sufficient force to create bumps as it enters the holes.

Once peeled off, you should be able to measure the bumps to get the hole sizes.

I think it would be difficult to handle, however, without breaking it.

As an alternative, especially as you have access to the inside/reverse, is to use a silicone molding compound of some high Shore value (hardness). The clay might be useful to create an inner dam as well as a container of sorts for the silicone on the outside.

Silicone molding material, especially the high hardness stuff, is quite durable. This should allow the portability and handling you require. Some compounds have minimal shrinkage, allowing for reasonable precision. It may be necessary to test sample holes to determine exact shrinkage levels, but it would be consistent across a specific range of diameters.

Expanding from the above suggestion would be to seal off the holes with adhesive tape rather than modeling clay or other dam material.

The ideal situation would be that your curved surface has a horizontal orientation, minimizing the damming requirement and the amount of silicone used.

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You can mark a masking tape in inches or centimetres and tape it along the visual prominent features, such as along the ridge, or length or any axis that would yield more info as to the dimension and geometry of your shape.

Then using those measurement you can build a 3d model in a drafting program like Autocad or free wares such as google Sketchup. Then you have a model of your shape which you can measure in any direction or print a 3d print-out

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