Getting Measurements from Photographs
Measuring from photographs
A long while back, I remember a letter to the editor of one of the home shop engineering magazines asking whether it was possible to obtain measurements from a photograph.
Coming from a semi geographical sort of education, I was familiar with photogrammetry and can generally see 3d from a pair of stereo photos without using a stereoscope. The easiest way is actually to put the images side by side but with the left hand image on the right, then to look at the images cross-eyed. It might take a bit of shuffling of the image positions and it takes a little practice, but after a while, that imaginary 3d image that you get in the middle can be scrutinized.
I’ll not go into the theory of photogrammetry, there are several links from photogrammetry societies which do that very well. But it is possible to manually, mechanically or digitally obtain accurate 3d measurements from photographs.
This divides into two systems:
Aerial photogrammetry, where distances are large and corrections are necessary for things like the refractive index of the atmosphere.
Close range or architectural photogrammetry, where you are more interested in 3d detail and views that are not necessarily on a regular parallel grid.
Digital cameras speed up the image capture, and in the case of the better digital SLRs provide almost the accuracy of traditional “metric” cameras. Rollei still make film and digital metric cameras, at a price.
Probably the easiest way to get into this is to use Arpenteur, a web based photogrammetry programme.
Photomodeler provides one of the lowest cost options and has excellent free tutorials to download. Its’ disadvantage is that it does not allow you to view your photos directly in 3d, this is not such a problem on engineering structures, but on say a rock slope, does present a problem.
Photomodeler light used to be available as shareware, but is now very difficult to find.
Both Adam and CSIRO (Sirovision) in Australia have mining orientated packages that allow the automatic generation of a 3d point clouds (similar to what you would obtain with a laser scanner), that you can then render with the image from the photos, allowing easier examination and measurement of natural structures. particularly ones that you don't want to go near in person. Their web sites have sample images.
Most of these measurements can be linked to form 3d cad models for use in CAD, CAM and CNC machining.
So, that water pump body you needed for the 1920’s tractor that the guy would not sell you, can be photographed, a 3d model made in the computer and your uncle, Bob, who works in a machine shop can set one of the machines to make a couple of them on the night shift…
A long while back, I remember a letter to the editor of one of the home shop engineering magazines asking whether it was possible to obtain measurements from a photograph.
Coming from a semi geographical sort of education, I was familiar with photogrammetry and can generally see 3d from a pair of stereo photos without using a stereoscope. The easiest way is actually to put the images side by side but with the left hand image on the right, then to look at the images cross-eyed. It might take a bit of shuffling of the image positions and it takes a little practice, but after a while, that imaginary 3d image that you get in the middle can be scrutinized.
I’ll not go into the theory of photogrammetry, there are several links from photogrammetry societies which do that very well. But it is possible to manually, mechanically or digitally obtain accurate 3d measurements from photographs.
This divides into two systems:
Aerial photogrammetry, where distances are large and corrections are necessary for things like the refractive index of the atmosphere.
Close range or architectural photogrammetry, where you are more interested in 3d detail and views that are not necessarily on a regular parallel grid.
Digital cameras speed up the image capture, and in the case of the better digital SLRs provide almost the accuracy of traditional “metric” cameras. Rollei still make film and digital metric cameras, at a price.
Probably the easiest way to get into this is to use Arpenteur, a web based photogrammetry programme.
Photomodeler provides one of the lowest cost options and has excellent free tutorials to download. Its’ disadvantage is that it does not allow you to view your photos directly in 3d, this is not such a problem on engineering structures, but on say a rock slope, does present a problem.
Photomodeler light used to be available as shareware, but is now very difficult to find.
Both Adam and CSIRO (Sirovision) in Australia have mining orientated packages that allow the automatic generation of a 3d point clouds (similar to what you would obtain with a laser scanner), that you can then render with the image from the photos, allowing easier examination and measurement of natural structures. particularly ones that you don't want to go near in person. Their web sites have sample images.
Most of these measurements can be linked to form 3d cad models for use in CAD, CAM and CNC machining.
So, that water pump body you needed for the 1920’s tractor that the guy would not sell you, can be photographed, a 3d model made in the computer and your uncle, Bob, who works in a machine shop can set one of the machines to make a couple of them on the night shift…
posted by Keith at 10:30 p.m.
1 Comments:
Very nice. I knew of the new techniques that use a laser to make a 3D model of an object to feed the specs to the machinery. Hadn't heard of these systems before.
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