Photo Measuring for Trunk Modeling

General discussions of measurement techniques and the results of testing of techniques and equipment.

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#1)  Re: Photo Measuring for Trunk Modeling

Postby DougBidlack » Fri Feb 08, 2013 12:01 am

Bob,

very impressive!  I would not have thought that the difference would amount to less than 2%.  Just out of curiosity what would you say the time difference might be between the two methods in this particular example.

I've been thinking of trying to model some trees that I've planted because I'm very interested in growth.  If the field work is fairly fast with this technique it will likely be a real winner for the project that I'm thinking about.

Doug
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#2)  Re: Photo Measuring for Trunk Modeling

Postby Larry Tucei » Fri Feb 08, 2013 12:02 pm

Bob,  I would like to try your photo process on the Ms Champion Live Oak combined with your sine volume formulas that you made some years back. I think we could get a very close estimate to the volume of this big tree.  I estimate it would be somewhere between 4000-5000 cubic feet. In comparing it with the Middleton Oak I think it is very similar in size.    Larry
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#3)  Re: Photo Measuring for Trunk Modeling

Postby dbhguru » Fri Feb 08, 2013 1:07 pm

Doug and Larry,

  Doug, the amount of outdoor effort is minimal. You identify the tree to be modeled, locate a spot from which to photograph it, identify the points along the trunk/limbs to be measured, place a reference object in the photo, shoot the distances and angles to the reference object and each spot on the tree that is to be measured, and take the photograph. Everything else occurs indoors on your computer. With a template spreadsheet set up, all you have to do is import the image, mask all the distances to be measured with line shape objects, and post all the data into the template. I can describe the process in greater detail, maybe asking for Ed's assistance. His detailed instructions are almost always better than mine. So, the process using photography is much quicker than with the monocular, and the more measurements taken for a tree (or group of trees) within one photograph, the greater the efficiency of the photographic method.
 
   The method can be made even more efficient with the use of Visual Basic for Applications, the macro language of Excel. It would be tricky, but an Excel macro could be developed to automatically read the dimensions of the masking lines and post them into cells within a template. A strict protocol would have to be followed such as proceeding from left to right and bottom to top in terms of placing the masking lines. The reference object would be covered first regardless of where it appeared in the photo, then the sweep from left to right. The more automatic this approach, the sophisticated the macro would need to be, especially if multiple trees were being modeled through a single photograph. At the beginning, we would need to keep it to a single tree so that the first mask would be the reference object, and all subsequent masks would be on the trunk going from bottom to top. Each limb would be a separate image.

Larry,

  You have me at your service. We should begin by modeling a simple form, perhaps a tree in your yard or neighborhood to work out the kinks. Once we have covered all the situations, we could go live. I'd dearly love to thoroughly model a big live oak this way. It would require many photographs. As an absolute minimum, one for the trunk and one for each major limb, but I expect that each limb would have to be broken into 2 or probably 3 photographs. We have to clearly see the targets.


NTS,

  BTW, there are other methods of getting measurements of objects in a photo other than Excel. I'm presently experimenting with ImageJ, image processing software. Matt put us onto that software. But ImageJ is not for the faint of heart. It is extremely sophisticated, but the measurements you can take off an image are a little better than those from Excel.  
Bob
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#4)  Re: Photo Measuring for Trunk Modeling

Postby edfrank » Fri Feb 08, 2013 4:00 pm

 The method can be made even more efficient with the use of Visual Basic for Applications, the macro language of Excel. It would be tricky, but an Excel macro could be developed to automatically read the dimensions of the masking lines and post them into cells within a template. A strict protocol would have to be followed such as proceeding from left to right and bottom to top in terms of placing the masking lines. The reference object would be covered first regardless of where it appeared in the photo, then the sweep from left to right. The more automatic this approach, the sophisticated the macro would need to be, especially if multiple trees were being modeled through a single photograph. At the beginning, we would need to keep it to a single tree so that the first mask would be the reference object, and all subsequent masks would be on the trunk going from bottom to top. Each limb would be a separate image.


1) Basically, if I understand this right, the idea behind the photo measurement is that the rate of change in perspective (trunk width) should change smoothly in a linear fashion as the target gets farther away.  Your formula essentially is calculating the equivalent of the optical scaling factor based upon distance from the lens and apparent width of the reference object, much like is provided with a reticuled monocular.
2) The process for modeling the volume of a tree using photo measurement proceeds in the same way as with the monocular.  The distance to each measurement and height above eye/photo level can be measured using the rangefinder and is input into your spreadsheet
3) I am not sure why you would need to maintain the line direction consistently, but if you say so.  It really isn't a problem to do it this way.  
4) Does the line across the tree need to be exactly horizontal or vertical, or can it be drawn at an angle?
5) So long as the focal length on a zoom lens does not change from image to image on a single tree the same scaling factor should work for multiple images in a set.  So you could first take an overview photo to see how the tree is formed.  You would need to make a sketch of the tree structure and measuring points to keep track of the position of the measurements.  You could zoom in as close as possible so the base of the trunk and the reference scale filled most of the width of the image.  Without changing the focal length you could then shoot all of the targeted points.  (Ideally you would have multiple images that could be stitched together to form a pan of the entire tree, but if parts were missing it would not really matter for measurement purposes)  This would assure that the image being measured for any measurement was as large as possible.  This would help alleviate the problem of tiny widths in an image of the entire tree in one photo.
6) How do you determine the length of a branch or trunk segment that isn't vertical in the volume measurement protocol?  The angle of the trunk or branch might not be perpendicular to the viewer? (Short of doing an azimuth and plotting the positions of the end points of the segment in 3D.)
7) I would think it would be better to try to model just one tree per photograph, or at least simply treat each different tree as a separate entity on a separate spreadsheet page, rather than trying to do it all on one single spreadsheet page.  it would be a nightmare to keep your data in order if multiple trees were on a single sheet, and if it makes the macro harder to write, why bother?  it seems a bad idea all around.

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#5)  Re: Photo Measuring for Trunk Modeling

Postby edfrank » Fri Feb 08, 2013 4:17 pm

Bob,

A couple of other points:

8) are the measurements to the tree to the front side of the tree with the spreadsheet correcting for the roundness of the trunk or to the edge of the tree?
9) If Excel will do the calculations, that is a big advantage over the photo software unless it will do the calculations also.  It will be easier for people to use Excel and it will get used more even if the photo software gives comparable results.

Edward Frank
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#6)  Re: Photo Measuring for Trunk Modeling

Postby Larry Tucei » Fri Feb 08, 2013 5:32 pm

Bob,  I have a good size Darlington Oak in my backyard that we could use as a model. I'll get some photos from 40'. Perhaps I should get shots from one side then at 180 degrees from the other side? You would not see all the limbs from one side in many cases.  In the case of a large Live Oak I think we would need shots from at least 2 sides maybe 3. Larry
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#7)  Re: Photo Measuring for Trunk Modeling

Postby dbhguru » Sun Feb 10, 2013 4:12 pm

NTS,

    I continue to chip away at the Photo-Excel method for measuring diameters at a distance. We do that with monoculars and we can do it with instruments such as the TruPulse 360. The LTI RD1000 was designed to measure diameter at a distance. All these approaches have their strengths and weaknesses. The monocular is the most accurate tool in the toolchest, but visibility can be a problem in seeing the edges of a trunk. If you can see the target clearly and the reticle marks against the target, then accuracy is assured. But if the weather is uncooperative and/or the target fuzzy, the monocular shows its weakness. The TruPulse approach depends on the accuracy of the digital compass. It's pretty good, but needs to be calibrated a lot. If you're around magnetic fields when using the TruPulse's compass, forget it. In addition, it is an expensive device. The RD1000 is also expensive. It works well over a rather narrow range, but as distances get greater, a change in one vertical bar on the display represents an unusually large change in diameter, and one more unit or less at a distance is not that discernible. These are the things you discover once you have the unit. Enter the Photo-Excel method. Just about everyone into serious tree measuring has a laser rangefinder, a clinometer, a digital camera, and a computer with Excel on it.

   The attachment shows the results of an ad hoc experiment late yesterday afternoon. While sitting at my desk in the basement, an idea hit me. I attached an 18" ruler to a post outside the window at 10 feet away. I then took a photo of the trunk of a Northern Red Oak in the back. I used the reticle to measure the diameter at a spot on the oak. I measured the diameter at the point photographically. The spreadsheet shows the results. I'm going to conduct another test the same way later today and will report the results.

    BTW, Michael Taylor sees merit to the Photo-Excel method and wants to automate it with VBA. I can think of nobody better to do it.  

Bob
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#8)  Re: Photo Measuring for Trunk Modeling

Postby dbhguru » Mon Feb 11, 2013 8:03 pm

NTS,

 The attachment speaks for itself. I hope that some of you will want to give the method a test run As a team, we can perfect it further. Michael Taylor is definitely going to help automate it. But some of you may think of improvements.

Bob
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#9)  Re: Photo Measuring for Trunk Modeling

Postby dbhguru » Sat Mar 02, 2013 11:19 am

NTS,

   Returning to the photo measurement method using Excel, the image below shows the efficacy of the method. The Lyndacker Pine measures 17.8 feet in girth at breast height. In the photo, I've chosen the location on the trunk corresponding to Matt Lyndacker's chest height location. Monica stretches out to the left against the trunk. Here height at this point is about 5.5 feet. Here full height standing erect is between 5.6 and 5.7 feet. The remarkably close match of measurements (tape stretch vs. photo-Excel) still amazes me. I keep waiting for a mis-match to occur in which I can't explain the difference. So far that hasn't occurred.

               
                       
LyndackerPinePhotoAnalysis.jpg
                                       
               


Bob
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#10)  Re: Photo Measuring for Trunk Modeling

Postby dbhguru » Mon Mar 04, 2013 9:42 am

NTS,

  Below are the results of yesterday's photo measurement exercise. I decided to apply the simple photo-measuring method to the big double pine about half a mile upstream from the house. I keep close tabs on its height since it is one of a mere handful of trees in the lower Connecticut River Valley that reaches the threshold height of 140 feet. Yesterday's re-measurement yielded 140.3 feet. I have the variance down to 0.2 feet from the range of 140.1 - 140.3 feet.

  Since the pine is a double, the form of the lower trunk is not circular. I think the Broad Brook Pine's form approximates an ellipse. It is definitely not circular. So measuring the girth with a tape and then calculating a diameter based on a circle should exceed the minor axis and fall short of the major axis. At the least, the photo-measured width of the major axis should exceed the circular diameter. That is what happened yesterday.

               
                       
PhotoAnalysisBroadBrookPine.jpg
                                       
               


  The point of measurement shown in the image is on the uphill side of the tree. I should have taken the time to have repeated the process at 90 degrees going around the trunk to catch the minor axis. I was floundering around in the snow, which is still quite deep. So, rested and then I decided to go a little farther upstream to a white pine stand that I visited fairly often back in 2007 when I was recovering from the shingles. It is a handsome stand, but devilishly difficult to measure. When the hardwoods leaf out, the measuring season ends. Well, outside the snow cover, yesterday, measuring conditions were ideal. I confirmed four new 130s with the tallest at 137.0 feet. This places the number of 130s in the Broad Brook corridor at 10. I plan to return to the stand today and resume the documentation.

   I'll also take the minor axis measurement of big double. Since it doesn't take much time to take a photo of the trunk with a reference object, I can be productive when in the field. All the work is done back at my computer in comfort. The key is to be organized in terms of what you want to measure for a tree when on site.

Bob
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