Parallax method revisited

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#1)  Parallax method revisited

Postby dbhguru » Tue Jun 05, 2012 11:26 am

NTS

    The image below shows the Parallax method for measuring tree height as developed by Michael Taylor. Both Michael Taylor and I have presented versions of this method in the past. Michael's diagram is the clearest.


               
                       
parallax.JPG
                                       
               



     This method has received little attention from NTS members, because is suspect that it is not intuitive. Also, angle and distance errors have a magnified effect. However, the revised attaches Excel spreadsheet does all the work. I've removed all the formulas that I included in the previous spreadsheet. Hope is is a little more user friendly.

Bob
Attachments
ParallaxMethod-2.xlsx
(19.96 KiB) Downloaded 35 times
Robert T. Leverett
Co-founder and Executive Director
Native Native Tree Society
Co-founder and President
Friends of Mohawk Trail State Forest

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#2)  Re: Parallax method revisited

Postby M.W.Taylor » Mon Jun 25, 2012 3:19 pm

Bob,

Thanks for revising the spreadsheet. My description of the illustration is not very clear.  Much appreciated.

Michael Taylor

WNTS VP
landmarktrees.net
California Big Trees Coordinator For American Forests
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#3)  Re: Parallax method revisited

Postby dbhguru » Mon Jun 25, 2012 9:17 pm

Michael,

  No problem. We are gradually accumulating spreadsheet solutions to the simpler measurements that we do. I can't imagine the calculations needed in your cloud mapping. That's a whole different level of measuring. Congratulations.

Bob
Robert T. Leverett
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#4)  Re: Parallax method revisited

Postby M.W.Taylor » Sun Jul 01, 2012 3:54 am

Bob,

That is my older version of the Parallax Formula. It does not work very well for off-level terrain. I have a newer version that works for off-level ground. I did a write-up on this here:

http://www.landmarktrees.net/parallax%20method.html

http://www.landmarktrees.net/newmeasure.html

New proposed name is Parallax 3D. Ground level changes can throw a wrench into the original formula.

I like this method in that both heights must agree. If they do not the surveyor either hit different tops at the two views or took one of the angles or distances incorrectly. The two heights being in agreement is a way of self checking your #'s.

Michael Taylor

WNTS VP
http://www.landmarktrees.net
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Screen Capture Of Parallax 3D
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#5)  Re: Parallax method revisited

Postby dbhguru » Sun Jul 01, 2012 1:40 pm

Michael,

   Yes, this adjustment for a slanting baseline is critical, and the cross-check for the two determinations is key. Given some time, I plan to go through an analysis of error magnitude on the method for errors of up to +/- 0.5 degrees and distances of +/- 0.5 feet. I use differentials so really large errors aren't appropriate to this form of analysis as I realize you know.

    Right now,I'm taking alittle vaction form the math and absorbing the sights and sounds of the western expanses. Hope you are doing well and I look forward to more big tree confirmations from you and others out there in California and Oregon.

Bob
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