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Home arrow Archives   The American Surveyor     

Mapping Tree Footprints Print E-mail
Written by Christopher Bahr   
Friday, 25 October 2013

A 2.922Mb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE

Michael Taylor, a resident of small-town Hyampom, California, has a very unique hobby. Taylor is a member of The Native Tree Society (NTS), an interest group which includes some of the most renowned forest researchers in the world among its members. Known as "tree hunters," Taylor and other NTS members are on a search for the largest, oldest, and most unique trees in the world. According to the NTS, tree hunters aren't just looking for spectacular trees, they also "... bring back measurements, observations, and descriptions of the places they visit." And this is where Taylor's specialties lie.

Having co-discovered the tallest known tree in the world, a 379.3-feet-tall coast redwood now named "Hyperion," as well as discovering the second and third tallest trees in the world, Taylor is well-known among the tree-hunting community. His largest project currently involves co-authoring Dendromorphometry—­the Art and Science of Measuring Trees in the Field, a book all about tree measurement. Taylor is now evaluating the effectiveness of different systems for collecting various tree measurements, which will be included in the book.

In 2011, Taylor received a donated rugged handheld--the Archer Field PC®--from Juniper Systems. Taylor said of the Archer, "Upon first handling this little tank-like PDA, I got the impression I could leave it out in the woods for a year or two and it would still power up and work just fine if recovered." Loaded onto the Archer was Laser Technology Inc.'s MapSmart Field Mapping Software, designed especially for ease-of-use. Taylor uses this system to map tree footprints and to generate 3D surface point clouds for tree volume determination

So just what is a tree footprint? Imagine if you could trace around the outside edge of the bottom of a tree trunk, right along the line where the trunk meets the ground, the resultant shape that would be drawn would be the tree's footprint.

Take, for example, a former American Forests champion ponderosa pine known by the name of Bear Wallow. Taylor first collected data about the giant tree's footprint by standing at various positions around the tree, and using a laser rangefinder (the Impulse 200 LR) to collect as many survey points around the base of the tree as possible from each position. He then imported the files from the Archer to an interactive program in Excel on his laptop, where the collected data points could be tilted and rotated in three dimensions.

For comparison purposes, Taylor also mapped the footprint of a much smaller oak tree behind his home as a test to see how well the Archer/MapSmart/Impulse 200 LR system would work on a smaller scale. With much less surface area than the huge ponderosa, the smaller oak tree provided much more opportunity for error, since each error in the footprint would show up more profoundly in the survey. Taylor's logic in mapping the oak tree's footprint was, "If I can map this irregular and tiny oak tree, I feel I can map any larger tree in the forest." And he was pleasantly surprised. "The results were surprisingly good," he said. "The survey itself was much faster than expected."

The problem most people run into when surveying tree footprints is determining where the trunk ends and the ground starts. To overcome this problem Taylor used a prism and pole to project the survey to a more clearly defined position directly above the footprint point. This allowed him to create a footprint in the same proportion and shape floating above the actual ground reference point.

Another issue that may arise when mapping tree footprints is that there is a three and one-half inch off-set of scope to laser on the Impulse 200 LR. Taylor accounted for this difference by simply pointing the laser three and one-half inches above where he wanted to map a point.

To collect more measurements on the ponderosa, Taylor also used the system to create a 3D surface point cloud of the tree's trunk in order to accurately determine its volume. He did this by mapping over 2,500 data points on the surface of the trunk, and then imported the data into Excel on his laptop. Because this use was outside the sphere of the software's intended use, he found that after collecting about 800 data points, the MapSmart software began to slow down, taking much longer to calculate each point. To work around this, he conducted three separate surveys and later merged the data. This approach worked perfectly, and the resulting 3D surface point cloud is really quite remarkable.

Taylor's work in evaluating the Archer/MapSmart/Impulse 200 LR system will be addressed in the upcoming book he is co-authoring and will help to influence the way many tree hunters collect tree measurements in the future. "I have not found a better set of tools for the job," said Taylor. While his use of the system is unique, the data collection techniques he practiced are useful in many different applications. For the regular tree hunter, the system provides faster, more accurate measurements on the search for the largest, oldest, and most spectacular trees in the world.

Christopher Bahr is a technology writer in eastern Oregon, where he enjoys tinkering with electronics, kayaking, and cooking in his brick oven.

Equipment used:

• Impulse 200 LR
• Trupulse 360B
• MapStar angle encoder with quick-release tribrach adapter
• Turck interface cables with RS-232 adapter & remote trigger
• Heavy-duty aluminum tripod (for tribrach mount) with quickadjust sliders 
• Plumb bob  Reference tags and ground spike
• 2 Seco thumb-release tripods
• 2 extra quick-release tribrach adapters with plumb bob hooks
• Prism pole
• Seco Mini Prism & Leica 360 Degree Mini Prism
• Brackets and adapters for Archer Field PC and Impulse 200 LR

A 2.922Mb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE

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