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Can anyone suggest a source for, or methods to fabricate target scales to allow accurate measurements to be taken from photogrammetry images?  I've seen examples of target scales with machine readable circular codes and other useful scaling aids, but haven't found a good affordable source for them.  I've also heard that some photogrammetry software packages come with printable coded scales that can be attached to a suitable support, but I don't see this in the trial version of Agisoft's software that I have.  Some different sizes/lengths would be useful for smaller objects as well as for larger objects and scenes (within the limits of close-range photogrammetry).  I've been using various metal scales, a foldable wood ruler, and a contractor's level, but would like to get the most accurate measurements possible.

 

Many thanks!

 

Taylor

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Taylor ,

 

We made own a couple of different times but are actually looking into getting some printed options. We hope to have some better ideas about sources soon. We are going to the field next week so not sure if that soon.

 

PhotoScan professional has printable coded targets but not target sticks or scale bars. We hope to find out about cost of scale bars that have coded targets and some other things.

 

Bug me or this forum again in a while if no updates.

 

Tom

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Thanks, Tom!  I'll stand by for updates. 

 

In the meantime, here's an example I found that's not so affordable for me:

http://www.laser-engrave-it.com/Store/products/PhotoModeler-Complete-Target-Kit-%28294-Pcs.%29.html

Maybe if they'd offer some of these individually, instead of a package of nearly 300 pieces, it would make sense.  They look pretty nice, but it's not reassuring to see them offered alongside engraved Christmas ornaments.

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Looks like they actually have 3 different offerings, 2 are $400 and one is $800

 

http://www.laser-engrave-it.com/Store/categories/PhotoModeler-Target-Kit/

 

Still, it isn't totally clear to me what is the best solution.  I look forward to hearing more from Tom, and anyone else with photogrammetry target solutions.

 

Carla

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Since I don't work with coded targets, I prefer to create my own in Adobe Illustrator and have them printed on a heavy substrate like Alupanel at a sign printing company. This gives me the most flexibility in terms of target size. The target kits that are commercially available are generally designed for only one scale of project. If you're working at the macro-scale you'll need much smaller targets, and likewise for really big rock faces you'll need much larger ones. Macro-scale targets are a bit challenging since the imperfections of the printing process for signs becomes rapidly apparent. Some sort of custom etched solution is probably best in that case. 

 

Does Agisoft use coded targets in the way Photoscan does? Unless you absolutely need the coded targets, I wouldn't bother. 

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Just for clarity - Agisoft is the company and photoscan is the product. There are 2 levels of photoscan, pro and standard.  I think George may have meant Photomodeler.  I know they use coded targets.  I also know that photoscan pro will produce a pdf with targets for printing.  They aren't all the same, but they may not be coded the same way photomodeler does it.

 

I also know that Tom Noble has worked with lots of different photogrammetry packages, and has designed his own targets (more than once even!) As much as possible we want to recommend capture practices that work across software packages, which helps not only with the value of the data today, but increases the likelihood of reuse in the future.  I'll be interested to hear more about what Tom says his experience is on this related to targets.

 

Carla

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Thanks for the responses!  Carla, I have a trial version of Agisoft Photoscan Professional but haven't activated it.   I was going to ask where to find the .pdf with targets for printing.  I searched the Help menus, but couldn't find it, then I found it under Tools->Print Markers.  

 

I haven't used Photomodeler or coded targets myself, but thought I read somewhere that they allow the software to determine the position of the camera axes (pitch, yaw, roll) relative to x,y.z axes in the scene for more accurate calibration and measurements.  Maybe other photogrammetry software packages have other ways of dealing with this.  Someone local has offered to let me use their Photoscan Pro software with a full license, so I'm sure I'll learn more about it as I get more familiar with it.

 

Best,

Taylor

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Coded targets used to be essential in order to be efficient with PhotoModeler. Lots of circular targets, coded or not, also used to be necessary in order to quickly orient photos to each other, at least initially. No targets, coded or otherwise, are actually necessary for PhotoScan, or other software, including PhotoModeler these days.

 

However, targets are very useful for marking the objects used for scale and or control points. Circular targets are ideal because most software can actually assist in finding the center of the target very accurately - far better than human error will allow. If the circular targets happen to be compatible coded targets, PhotoScan and PhotoModeler can find them automatically, almost no user interaction required. AdamTech CalibCam finds the centroids of targets - like PhotoScan and PhotoModeler - very accurately but does not support or require coded targets. So coded targets can be very useful but not at all mandatory. 

 

PhotoModeler supports several variations of coded targets. The ones in the kit are the latest version, but those are not supported by PhotoScan.

 

As I said, we are in the process of redesigning the scale bars that many of you have seen - that we use all the time - and are going to look for sources to print. 

 

We have been in the field the last couple of days and are packing today for a week and a half in the field so I will have limited access to internet until July 2.

 

If I get done what we shot yesterday I might post some shots or data with some scale bars in action.

 

Tom

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Hi Folks,

 

I'm happy to report that CHI has partnered with Tom Noble on a calibrated scale bar product, which we are now offering for sale.  These are printed on DiBond for indoor and outdoor use, and are based on a lot of iterations that Tom and his colleague Neffra Matthews tried in the field.  We calibrate them because the printing process isn't precise enough for our needs.  We use previously calibrated "golden masters" in the calibration process and scribe the accurate data on each scale bar.  You can learn more and/or order a set here:  http://culturalheritageimaging.org/What_We_Offer/Gear/Scale_Bars/index.html

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