measuring base?

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

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sradivoy
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Re: measuring base?

Post by sradivoy » Wed May 27, 2015 11:31 am

sradivoy wrote:
Don wrote:Now we're talking! Good questions...I think that we would first need to decide if the center of the tree is the distance we're measuring, then decide how to best measure it...I agree with Matt that the more accurate 'reflection' of laser pulses come from the flatter surface. Reflections coming off the far sides are more likely to be 'scattered' or less strong.
When it really makes a difference, a parabolic reflector (they had hand held models the size of a salt shaker (1" diameter) that we used on the Criterion 300 (one of the earlier laser rangefinders, we used them in Alaska in the 1990's for traversing timber sales, etc.
Matt-
Your leaving the tape wrapped around the tree had me thinking of reflective flagging and whether there might be some advantage there?
-Don
The reason I was interested on the distance of the side edges of the trunk is that it approximates the distance of the central axis of the tree (assuming it isn't leaning). But I don't think the distance of the central axis is relevant to determining the height of the tree.
Scratch my previous comment up above. The distance to the central axis is very relevant in determining tree height. I learn new things as I go along with my posts, so bear with me..

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sradivoy
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Re: measuring base?

Post by sradivoy » Wed May 27, 2015 12:26 pm

One needs to be perpendicular to the slope where the left and right corners of the trunk occupy the same angle on your clinometer for the mid-slope estimate to work when viewed from a distance. If viewing the sloped tree from the side, one corner of the trunk will have a larger angle than the other corner. In that case I would take the difference between those two trunk corners and use that average angle for the sine value. I would also use that position in determining the base leg of the height as well. (Feel free to correct any mistakes with my reasoning btw.)

One may be able to reconcile the two approaches by using the side trunk measurement ONLY for the clinometer position and then take the nearest part of the trunk (the middle flat portion) just for the rangefinder reading at that same angle. Kapish?

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Don
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Re: measuring base?

Post by Don » Wed May 27, 2015 1:01 pm

sradivoy-
If you go back and review Bob's succinct and correct phrasing:

"The American Forests approved height for the purpose of crowning national champions is the vertical distance from the top to the level of mid-slope. There are many ways of obtaining this vertical distance, but If you measure vertically up from mid-slope to a convenient point, put a ribbon around the trunk at the point, kept in the horizontal plane, and measure vertically from the top down to the ribbon and then add the vertical distance from the ribbon down to the mid-slope point, you have the correct height of the tree. Shooting distance and angle from a vantage point to the side of the trunk may more closely approximate the mid-slope point, but is not as good as the ribbon method. You will still need to add a vertical offset if you are measuring a tree on sloping ground.",

you will find the truth of the matter...
Don Bertolette - President/Moderator, WNTS BBS
Restoration Forester (Retired)
Science Center
Grand Canyon National Park

BJCP Apprentice Beer Judge

View my Alaska Big Tree List Webpage at:
http://www.akbigtreelist.org

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sradivoy
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Re: measuring base?

Post by sradivoy » Fri May 29, 2015 10:23 am

dbhguru wrote:Stefan,

Yes, we all use the approximating methods for measurements that don't involve championships. So much of what one does depends on visibility.

Bob
Very true Bob. The approximating methods aren't meant to replace the more accurate prescribed method (which requires more physical contact with the tree) but rather to compliment it with a kind of short hand just prior to finding a superlative tree out in the field. If one can establish a consistent margin of error between the two one can improve the quick approximating method even further. At least that is my hope.

As a practical matter very few people will want to go through the trouble to formally measure a tree across a steep and treacherous ravine, and then make several trips back and forth to secure and retrieve a ribbon/tape measure unless they're pretty darn sure that that tree is in fact a contender. I'm trying to conserve energy for when I need it..

Stefan

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sradivoy
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Re: measuring base?

Post by sradivoy » Fri May 29, 2015 10:50 am

sradivoy wrote:
dbhguru wrote:Stefan,

Yes, we all use the approximating methods for measurements that don't involve championships. So much of what one does depends on visibility.

Bob
Very true Bob. The approximating methods aren't meant to replace the more accurate prescribed method (which requires more physical contact with the tree, and thus potentially harms it) but rather to compliment it with a kind of short hand just prior to finding a superlative tree out in the field. If one can establish a consistent margin of error between the two one can improve the quick approximating method even further. At least that is my hope.

As a practical matter very few people will want to go through the trouble to formally measure a tree across a steep and treacherous ravine, and then make several trips back and forth to secure and retrieve a ribbon/tape measure unless they're pretty darn sure that that tree is in fact a contender. (I'm trying to conserve energy for when I need it.)

Using a riticulated mooncular would be very useful for similar reasons as a preliminary measurement to actually measuring the girth of a thick tree with a measuring tape. These are all great tools to locating tall and thick trees prior to formal measurements. In fact it wouldn't be a bad idea to label those results as "preliminary estimates (or approximations)" when reporting as a way of differentiating between the two.

Stefan

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Will Blozan
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Re: measuring base?

Post by Will Blozan » Fri May 29, 2015 5:17 pm

From the Tsuga Search final report...
The reticle was also used to remotely measure the diameters of large trees spotted at long distances or over difficult terrain. It allowed a close approximation of diameter without having to access the tree. The use of the reticle techniques and the ENTS sine method proved to speed up fieldwork and expand our search capability from the immediate vicinity to those trees within our field of view. Direct contact with the subjects was not needed and the techniques provided quick, accurate results.
Will

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Don
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Re: measuring base?

Post by Don » Sat May 30, 2015 1:16 am

Will-
I quite agree, and in fact have found that the Celestron Cavalry 7 x 30 binocular with reiticle serves that specific purpose very well...when one takes an initial reading and averages it with a second one at 90 degrees (assuming it's possible from another remote viewpoint), quite a good acccounting of the dbh can be made, should one have to deal with a ravine, an intimidating bull in a field, or other such incumbrance...
-Don
Don Bertolette - President/Moderator, WNTS BBS
Restoration Forester (Retired)
Science Center
Grand Canyon National Park

BJCP Apprentice Beer Judge

View my Alaska Big Tree List Webpage at:
http://www.akbigtreelist.org

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