Setting up a GPS Arboretum

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Setting up a GPS Arboretum

Post by dlrossjr » Mon Feb 04, 2013 4:37 pm

I'm trying to develop an arboretum with GPS coordinates for trees on my middle school's campus and nature trail. I know that the handheld devices available to us only offer so much accuracy, but maybe they're close enough with some descriptions? This project is for the most part in the idea stage, though we do have handheld Garmin Etrex GPS units and a GPS camera, as well as about a mile of trail, with varying aspects and hydrology--some hardwood, and mixed hardwoods.

I do worry about putting too much investment into tree tags, though some sort of marker might be needed.
Thinking about some sort of plastic/ metal tacks, or paint markers?

If someone has some proven solutions, or important considerations I'd be happy to hear them.

Many of the larger trees we can find via Google Maps, and Google Earth.


Dave Ross

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Re: Setting up a GPS Arboretum

Post by pdbrandt » Mon Feb 04, 2013 5:22 pm

Hi Dave,

I created a google map enabled virtual tree tour of the trees on UNC-Chapel Hill a couple of years ago. It works great on a GPS enabled tablet or smart phone. Each GPS point has 3 pictures of the tree associated with it so that tour goers can be sure they are at the right tree. It also helps helps that the trees I chose to highlight were already tagged with metal plaques. Here's the link to the tour:

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Re: Setting up a GPS Arboretum

Post by edfrank » Thu Feb 07, 2013 11:03 am


I am sure you have looked over our BBS to find articles related to your question. I thought I would provide a few links anyway for reference. There are different kinds of GPS units with varying degrees of accuracy.

The U.S. government is committed to providing GPS to the civilian community at the performance levels specified in the GPS Standard Positioning Service (SPS) Performance Standard. For example, the GPS signal in space will provide a "worst case" pseudorange accuracy of 7.8 meters at a 95% confidence level.

The actual accuracy users attain depends on factors outside the government's control, including atmospheric effects and receiver quality. Real-world data collected by the FAA show that some high-quality GPS SPS receivers currently provide better than 3 meter horizontal accuracy.
This should be in most cases accurate enough to distinguish individual trees. There are sometimes other things that might affect the accuracy. The positioning is based upon both the accuracy of the location and accuracy of the GPS unit trying to relocate the point. So if the position listed is off by 3 meters, and the GPS unit error when trying to relocate the point is off by 3 meters, The errors could be additive or partially cancel each other. In any case they should be good enough. The key to good readings is to allow them to average the readings for long enough of a time. It measures the signals from several satellites and averages them. The longer the time up to a point, the better the location. So to collect location data let the instrument average for at least 2 minutes, and not more than 5. You can also check the locations on Google Earth if individual trees are identifiable. This serves as a double check for any transcription errors in the field data. Coupled with location descriptions people should not have any trouble locating the trees. We have some GPS location listings published for big trees at some of the state parks here in PA. Geocaching is a big hobby and they seem to find the caches, maybe looking at some geocaching sites might give you some tips.

Scott Wade works at Longwood Gardens near Philidelphia. He is measuring an mapping trees in the garden and putting up QR-Code Tags for some trees;

QR-Tags for famous Trees of Texas: This has some other links where they are doing QR-Tags and could get your internet searches started.

QR-Tags for Trees: This is our original discussion on the subject.

Good luck with your project. Give us some updates as your virtual trail progresses.

Edward Frank

"I love science and it pains me to think that so many are terrified of the subject or feel that choosing science means you cannot also choose compassion, or the arts, or be awe by nature. Science is not meant to cure us of mystery, but to reinvent and revigorate it." by Robert M. Sapolsky

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Re: Setting up a GPS Arboretum

Post by greif » Mon Sep 02, 2013 9:42 am

A couple things that might be of interest;
When you determine the GPS location of a tree, if your device has an option for taking many readings and averaging them, the uncertainty of location can be dramatically reduced (even with a better machine a single reading may be occasionally 100 ft off).

I use a Garmin Map gps 60csx for mapping trails (current model is now 62csx I think) and it is a step above most models in sensitivity. Even with thick wet canopy, fog, clouds, snowstorms, etc. it consistently reports 30ft or better accuracy.)

For tree tags a reasonably weather resistant tag may be made with a laser printer and plastic print media (most often used for printing waterproof maps such as; )

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Re: Setting up a GPS Arboretum

Post by Don » Mon Sep 02, 2013 3:52 pm

You've got an interesting project that will provide learning opportunities for the staff and the middle-schoolers!
Having come from the era when GPS activities went better with advance planning (timing your activity to line up with the best positioning of the satellite constellation), today's GPS equipment is a whiz to work with in comparison.
My own GPS is a Garmin 62 csx and is a good standard, whose price has come down nicely with the advent of late model "smart" GPS's. Having WAAS enabled GPS helps, reducing positioning error to 3 meters ( Garmin 62csx'x and better also have 'memory' that retains relative constellation location while passing under sections of dense canopy. All that said, user responsibility is required to note your GPS's PDOP (Percent dilution of precision, if I recall correctly), which is kind of like signal strength/accuracy, dependent on the array of satellites providing the best "4D" configuration.
Best of all, is that which bridges the gap between the satellites so far away and the ground you're wanting to walk on, and that is GoogleEarth. An excellent learning opportunity, GE allows you to orient to locations visually, as well as by coordinates. Developing skills in photo and digital image interpretation can lead to great careers in photogrammetry and remote sensing (check out issues of Photogrammetric Engineering and Remote Sensing, to see if there is "anything new under the sun"!
A number of our NTS members have used a wide variety of software and smart phone apps that will further enhance learning opportunities, presentations, and outdoor programs.
Don Bertolette - President/Moderator, WNTS BBS
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