Photogrammetry

[John Candy]

There are a number of ways to produce 3D objects but the basic routes are using a CAD/drawing type package, using a programming method (e.g. Openscad) or to digitally copy a solid object and then process the resultant data.

The digital copying of the solid object splits into two alternatives. The first being via a scanner (they use various techniques including lasers) the alternative being photogrammetry.

Photogrammetry involves taking numerous photos from all angles (usually from 50 into the hundreds or more) either from the ground or from the air, using a drone.
The resultant images are then processed (by a high spec PC) to produce the 3D object.
The output can be exported into various artistic formats including those suitable for 3D print applications.

So why this new topic?
Yesterday, I took delivery of a new PC with the intention of experimenting with photogrammetry and am getting to grips with 3DZephyr, the software package which carries out the processing.
Early days and I am still getting my head around the package but initial tests are promising, if far from perfect!

Anyone else here tried photogrammetry?

John.

[Doddy]

Yes, I have a 3D printed photogrammetry turntable now being rebuilt with an upgraded, read 'larger diameter' turntable with automated positioning and photo collection.

In addition, a project I ran a few years before my current health problems was to obtain thousands of photos* (and audio) taken at Ryde (Isle of Wight) and Acton museum for the 1938 tube stock, which was still in operation on the Isle of Wight at the time of my visit. This project has the addition of a relatively cheap acquisition of an OO gauge EFE set of four London Transport cars to go with a previously obtained Network SouthEast IOW Dinosaur liveried two car train for dimensional comparison. Both Bachmann (EFE)* and N gauge Revolution trains will each have new 1938 stock models for retail soon. (* OO gauge already released)

Project documentation:

• Onboard and Lineside Audio taken along the entire length of the Isle of Wight line
• Side and roof photos taken at Ryde Station (on the Hovercraft bridge)
• Underframe photos taken at Ryde St John's Station and Action LT museum
• Internal photos taken at Acton LT museum (seats, lights internal fittings and flooring)

Ordinarily you would move around the subject to take photos from different angles, but in my case I let the train come to me and as it passed by I ran my camera in burst mode to make thousands of photos as it passed, in the museum photos I panned the camera in burst mode to achieve the same result.

Thankfully, when I was at Ryde it was a very sunny day and this enabled plenty of shadows to be cast that allows better light separation for 3D processing.

[Nick]

John,

I'm always interested in applying new technologies to our hobby. I hope you will keep us informed about how this develops and the sort of projects you are using it for. One thing that occurs to me is that a solid model created in CAD is usually made up of a set of components (which may also be called parts, assemblies, etc). In the case of a locomotive, probably hundreds of them. And that is necessary because each component will be made separately using different materials and methods.

Now if I understand it right, photogrammetry will produce a single solid model of the object photographed. Can it reproduce the interior of an object (assuming one can photograph the interior), and can it "dismantle" the solid model into components? The second of those would, I suspect, be a considerable programming challenge. And if operator intervention is necessary, how would the operator control the dismantling process?

I'm simply seeking information, particularly as it might relate to my own interests in the hoibby.

Nick

[John Candy]

Nick,

A "mesh" shell is produced by 3DZephyr which is rendered as a hollow 3D object (i.e. like an empty eggshell) and that is exported as an STL or OBJ file (which is then input to Cura or similar prog).
How it prints in 3D is controlled by the program which produces the Gcode (the code understood by the printer). Using the thickness of wall and "infill" settings, along with (removable) supports for overhangs/hollow parts, hollow objects can be printed.
I did a very quick "rough and ready" example (attached) of the Zephyr rendering to illustrate.
You can use the method on the interiors of buildings : You are only limited by your photographic skills and the power of your PC.




Regards,
John.
 

[Doddy]

Can it reproduce the interior of an object (assuming one can photograph the interior), and can it "dismantle" the solid model into components? The second of those would, I suspect, be a considerable programming challenge. And if operator intervention is necessary, how would the operator control the dismantling process?

Nick,
The answer is NO and NO. Just like Laser scanning technology, Photogrammetry is effectively a surface scanning system only. Great if you are scanning diesels and other solid bodied objects as a mesh. Although there is nothing stopping you scanning dismantled locomotive parts like boilers, whistles, steam domes, chimneys etc. Otherwise, a reliance on deconstructing the scans will require access to CAD software, decent engineering drawings and or a good sense of model railway development.

For example, Hornby used a flying drone to initially scan the overall bodyshell of the Class 71 at Barrow Hill, but required detailed laser scans of bogies, wheels and fixtures at ground level. The internals have to be designed with model locomotive fittings like motors, drive shafts, chassis blocks, Sound Decoder and electronic control PCB's.

Rapido used ground based lasers for scanning the APT-E and Stirling Single, both options use lasers that produce a solid object mesh that requires further CAD development.

Photogrammetry is just an inexpensive 'hobbyist' level data acquisition technique compared to more accurate laser technology, but also requires significant CAD development including much artefact removal, to take it to the stage(s) of producing individual components.

Hornby drone scan of Class 71 https://www.youtube.com/watch?v=nbSckKgXAUY

[Doddy]

A description of Rapido Trains New Alco PA-1 Locomotive and 3D Scan!

https://www.youtube.com/watch?v=erdozXTWrXw

[John Candy]

Photogrammetry is just an inexpensive 'hobbyist' level data acquisition technique compared to more accurate laser technology

Robert,
I have to question that statement: Below is an extract from
https://formlabs.com/blog/photogrammetry-guide-and-software-comparison/

<Quote>
Photogrammetry is used in numerous areas of application:
    Architects use photogrammetry for site planning, construction monitoring, and visualization rendering.
    Artists can document or convert a piece of an existing artwork, sculpture, or nature into something new.
    Archeologists can virtually map out and explore undiscovered areas of the world's lands and oceans.
    Designers and engineers who need to reverse engineer an existing object or custom-fit new parts onto it.
    Quality control in manufacturing processes is significantly aided by the use of photogrammetry.
    Game developers can save time designing props and environments by using photogrammetry combined with semi-automatic 3D modeling workflows.
    Paleontologists can capture fossils and bone beds and determine the best approaches to exhumation, jacketing, and preservation as well as document and share their findings. Detailed 3D maps of a site can more easily reveal fossil locations.
    For cartographers, geologists, surveyors, and topographic mappers, photogrammetry radically speeds up the process of mapmaking.
    Forensic researchers can capture crime scenes in three dimensions in order to gain more insight into issues such as bullet flight paths, car crashes, and witnesses' lines of sight, or to create virtual training environments.
    Therapists and other medical professionals may scan parts of a patient's body for custom-fitting applications such as prosthetics and orthotics, shoes, and hearing aids.
    In the field of cultural heritage, pieces and monuments can now be preserved forever and virtually reconstructed and renovated.
    Museum curators can establish virtual collections to attract the public.
    Meteorologists use photogrammetry to determine the speed of tornadoes.
    Photographers now have an extra dimension to work with.
    Companies that want to offer a service to 3D print models of most precious possessions, pets, or family members.


Here is the result latest test:-

 

Regards,
John.

[Doddy]

John,

While photogrammetry lets you cover a large amount of ground quickly, it does so with a low degree of accuracy. 3D laser scanning on the other hand typically has a smaller footprint of data being collected, but it's collected to a higher level of accuracy.

I think you need to examine the capabilities of both techniques more carefully before you start lecturing me with sales blurb.

[Nick]

Thank you both for your replies, which were much as expected but it is good to have them confirmed. I have no plans to build any diesel locos so I'll stick with CAD for now. Unless I get a sudden urge to build an A4 ...

Nick

[John Candy]

Robert,

Sorry if you felt I was lecturing you : My intention was to draw attention to the professional applications of photogrammetry (not merely for "hobbyists").

I agree it is a case of "horses for courses" and it is a "broad brush" method.

Although my test subjects have been small (using  just a webcam and empty PLA spool as turntable!), simply to try out the software, the intention is to use it on large objects (e.g. buildings,statues. war memorials) and in conjunction with a professional drone pilot and commercial film/TV broadcast quality photographic equipment.

Regards,
John.