measuring base?

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sradivoy
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measuring base?

Post by sradivoy » Tue May 26, 2015 9:10 am

When measuring distance to the base of a tree with a rangefinder is it better to measure the central portion of the trunk that is closer to me or the edges of the trunk that is farther away? I usually get about a half yard difference in distance for the lower hypotenuse.
Last edited by sradivoy on Tue May 26, 2015 1:45 pm, edited 1 time in total.

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bbeduhn
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Re: measuring base?

Post by bbeduhn » Tue May 26, 2015 9:28 am

It'll be interesting to hear others' perspectives on this question. I always stick to the nearest part of the base of the tree when measuring. The distance does increase when shooting at the deepest visible part but accuracy may also be less. The part closet to the observer tends to be flatter in relation to the measurere so if your laser and clinometer readings are several inches off of the same spot, there really isn't much of an error. If your readings are several inches off on the deeper part of the tree, greater error may be introduced. In most cases, this error would be subtle but when going for accuracy it's better to control any error that we are able to control. Instruments tend be off slightly anyway, which is somewhat beyond our control, but we have to control what we can as well as we can so that we do not introduce further error.

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Matt Markworth
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Re: measuring base?

Post by Matt Markworth » Tue May 26, 2015 11:18 am

As long as you're using the same point on the tree for both distance and angle, then theoretically it won't make any difference. The slightly longer distance to the side of the base will be compensated for by a slightly different angle.

Although, practically speaking you may as well shoot the side of the base that is closest to you, because it should provide a better, more repeatable target.

If the tree is on a slope and isn't leaning, I like to measure CBH first (based on midslope), then leave the tape wrapped around the tree as a reference point for the height measurement.

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Don
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Re: measuring base?

Post by Don » Tue May 26, 2015 3:10 pm

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
Don Bertolette - President/Moderator, WNTS BBS
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sradivoy
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Re: measuring base?

Post by sradivoy » Tue May 26, 2015 4:02 pm

Matt Markworth wrote:As long as you're using the same point on the tree for both distance and angle, then theoretically it won't make any difference. The slightly longer distance to the side of the base will be compensated for by a slightly different angle.

Although, practically speaking you may as well shoot the side of the base that is closest to you, because it should provide a better, more repeatable target.

If the tree is on a slope and isn't leaning, I like to measure CBH first (based on midslope), then leave the tape wrapped around the tree as a reference point for the height measurement.

I like the idea of leaving the tape wrapped around the tree as a reference point for height. Not only are there fewer obstructions in terms of underbrush at CBH, but you can precisely line up the degree lines of the clinometer with the line of the measuring tape. The rangefinder can be lined up more accurately to that same spot as well. It's just a matter of adding 4.5' to the height measurement.

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sradivoy
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Re: measuring base?

Post by sradivoy » Tue May 26, 2015 4:08 pm

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.

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dbhguru
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Re: measuring base?

Post by dbhguru » Tue May 26, 2015 4:58 pm

NTS,

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.

If you have a reflector of the type Don describes, it should be placed on the ribbon on the uphill side - if the tree grows on a slope. Just keep in mind that height is to the mid-slope point since we assume that a horizontal plane passed through the base at mid-slope point comes closest to identifying the ground level where the seed sprouted.

Bob
Robert T. Leverett
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Co-founder and President
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Don
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Re: measuring base?

Post by Don » Tue May 26, 2015 8:27 pm

For example...while there wasn't much slope at our Anchorage Cemetery, same rule applies on level ground.
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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 » Wed May 27, 2015 10:24 am

dbhguru wrote:NTS,

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.

If you have a reflector of the type Don describes, it should be placed on the ribbon on the uphill side - if the tree grows on a slope. Just keep in mind that height is to the mid-slope point since we assume that a horizontal plane passed through the base at mid-slope point comes closest to identifying the ground level where the seed sprouted.

Bob
I agree that the ribbon method is the most accurate method for measuring height and should be used in verifying and certifying exceptional trees in all instances. However, for scouting many tall trees over a long day its not the most practical approach. Likewise, I think that measuring the side edge of the trunk to the ground is more accurate than measuring the central(closest) part of the trunk because, as you correctly state, it approximates the mid-slope of the tree. Measuring from the central(closest) part of the trunk to ground level will invariably result in an exaggerated down-slope height for the tree.

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dbhguru
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Re: measuring base?

Post by dbhguru » Wed May 27, 2015 11:13 am

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
Robert T. Leverett
Co-founder, Native Native Tree Society
Co-founder and President
Friends of Mohawk Trail State Forest
Co-founder, National Cadre

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