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Thread: Photogrammetry?

  1. #1
    Join Date
    May 2010
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    Chicago
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    Default Photogrammetry?

    In rereading WB #246 I became intrigued with the idea of getting a 3D record of my interior hull shape before I fill it up with bulkheads and stuff. Considering Photogrammetry, does the camera need to be at a fixed location and pan around the boat, or can the camera move? Does it all need to be at one focal length, or can it zoom? I used 123D Catch when teaching a class, but in that situation (several years ago) the web site said to rotate around the object, but I have a really cramped shop and I could only get the whole boat in a shot from the bow and stern, any other angle wouldn't get the whole thing. Also, I would be interested in your recommendations for services that could stitch the images together into a valid 3D model. Attached is a snapshot from the stern, though the boat is now blocked and braced level in preparation for bulkheads.

    Please advise,

    Ken

    IMG_1365.jpg

  2. #2
    Join Date
    May 2012
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    UK. Cornwall, Suffolk.
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    3,414

    Default Re: Photogrammetry?

    By the time you figure all this out, you could have taken her lines with a plumbline, level, measure and pencil.

  3. #3
    Join Date
    Nov 2004
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    Port Townsend WA
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    10,553

    Default Re: Photogrammetry?

    Easy on a boat that small to do a mock up out of door skin.
    Jay

  4. #4
    Join Date
    Feb 2011
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    U.K
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    599

    Default Re: Photogrammetry?

    Photogrammetry is old hat. Take a look at Leica laser scanners. I could do a scan of your boat in about 10 minutes to an accuracy of 0.2mm

  5. #5
    Join Date
    Oct 2007
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    Alexandria, VA
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    120

    Default Re: Photogrammetry?

    does the camera need to be at a fixed location and pan around the boat, or can the camera move?

    The camera should move about the boat, with a photo every couple feet or so

    Does it all need to be at one focal length, or can it zoom?

    It can zoom, but be aware that doing so will change the f-stop, which may (unless the camera's very good at compensating for exposure) result in some areas of the resulting model being darker than others.

    any other angle wouldn't get the whole thing.

    You don't necessarily have to get the whole thing in every photo, as long as there's sufficient overlap for the software to build up the model sequentially. That said, doing it that way does open the door for accumulation of error. Control points at known coordinates can help counter that, if you have them.

  6. #6
    Join Date
    May 2010
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    Chicago
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    Default Re: Photogrammetry?

    Quote Originally Posted by Jay Greer View Post
    Easy on a boat that small to do a mock up out of door skin.
    Jay
    I don't really need to do this, I am just curious and interested. I actually have the full-size lofting that got me to this point, and all the molds, but haven't found a scanner big enough to make a digital version (6' x 8' for the section drawings) , and even if I had the scans, I would need to figure out how to make that into a 3D model that didn't have so-called manifold errors.

  7. #7
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    Default Re: Photogrammetry?

    Quote Originally Posted by keck314 View Post

    any other angle wouldn't get the whole thing.

    You don't necessarily have to get the whole thing in every photo, as long as there's sufficient overlap for the software to build up the model sequentially. That said, doing it that way does open the door for accumulation of error. Control points at known coordinates can help counter that, if you have them.
    Before I took it off the molds I scratched the interior at the sections and at the 2' waterline, and just today marked those more clearly with a fine felt-tip, do you think that would do it? Is there a software service you recommend?

    Ken

  8. #8
    Join Date
    Jan 2000
    Location
    Cushing, Maine
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    3,118

    Default Re: Photogrammetry?

    David Cockey who frequents the forum may check in. Short answer is that software is available, and the imaging does not need fancy cameras. Scanners like the Leica can do this as well but you will be in 5 figure land, not smart phone camera.
    Ben Fuller
    Ran Tan, Liten Kuhling, Tipsy, Tippy, Josef W., Merry Mouth, Imp, Macavity, Look Far, Flash and a quiver of other 'yaks.
    "Bound fast is boatless man."

  9. #9
    Join Date
    Jan 2004
    Location
    Rockport, Maine
    Posts
    336

    Default Re: Photogrammetry?

    The camera needs to move relative to the object, not stay in one location. The object needs to not move relative to the background (unless the background is plain such as a sheet of paper). Photos need to overlap, usually about 2/3 overlap is desired. Point clouds can only be calculated for areas which are in at least two photos taken from different locations, and there need to be some areas which are in a minimum of three photos taken from three different locations.

    Almost any digital camera can used as long as the photos are not blurred from motion, in focus, and have reasonably consistent exposures. More mega-pixels can be better, and sharper lenses are better. Unless the light is bright I use a tripod and move the camera and tripod between each photo.

    I'm not aware of any photogrammetry software which works well with lots of zooming. The best strategy is to use no more than three or four focal lengths (zoom settings). Also the images cannot be cropped in post processing - the full image needs to be used.

    Surfaces need to have some random visual "texture". Wood grain is great, particularly weathered wood. Painted surfaces can work if they are sufficiently dirty.

    My preferred software is the standard version of PhotoScan from Agisoft. www.agisoft.com Output from PhotoScan are point clouds and meshes. I usually obtain a point cloud with millions of points and a mesh with millions of vertices for boats.

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