Ed, Bart, Larry, Doug, Will, et al.
The attached Excel workbook just confirms what you already recognized, Ed. We can take multiple close up images from the same location and a reference object in any one of the images applies to the others. In the attachment, you'll notice three images of different parts of an oak named Pokey. I chose a spot in the dining room where I could see the tree to be measured. From there, I split a section of the tree up in three photos, keeping the same focal length throughout. Absolutely no change of camera settings. I also shot distances and reticle values to points in the three separate images. The reference object is the diameter at the location of the round marker near the base.
As you can see, I got extremely close measurements via the reticle and the photo process. My next step is to develop a clean spreadsheet template for this process and good user instructions. The method really does work on circular objects. With reference object of known dimension, laser rangefinder, clinometer, and digital camera, we can model trunks for volume. Throw in a compass to get horizontal angles and the process can be extended to limbs at all angles.
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Robert T. Leverett
Co-founder and Executive Director
Native Native Tree Society
Co-founder and President
Friends of Mohawk Trail State Forest