Google Earth to accurately measure canopy spread

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

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#1)  Google Earth to accurately measure canopy spread

Postby sfischer_16 » Fri Apr 22, 2011 12:35 am

I experimented with using Google Earth to measure the canopy of a silver maple.  Google Earth has a measuring tool that is known to be accurate (http://bbs.keyhole.com/ubb/ubbthreads.php?ubb=showflat&Number=1029963&site_id=1#import)

Attached are two images showing that the canopy of this tree is 115' at its widest and 78' at its narrowest.

Seems like this could revolutionize canopy measurement, as it is simple, free, repeatable and verifiable.  With experience ENTS could develop guidelines for correct usage to standardize it as a measuring tool.  (In some settings the outline of the canopy might be hard to detect.)  Note that the image includes GPS coordinates.  

The address I used to search for this tree is 800 Cricket Avenue, 19003.

To download Google Earth, go here:  http://earth.google.com

Give it a try (and verify my measurements)!

(By the way, this silver maple has a girth of 268".  Still need to measure height, which I plan to do by sighting with a carpenter's square held against my cheekbone.)

Steve
Attachments
CanopyWidest.PNG
Google Earth measurement of canopy at its widest: 115'.
CanopyNarrowest.PNG
Google Earth measurement of canopy at its narrowest: 78'

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#2)  Re: use Google Earth to accurately measure canopy

Postby edfrank » Fri Apr 22, 2011 1:12 pm

Steve,

This is a excellent idea. This certainly can be used where there is detailed enough imagery to do the measurements.  Such detailed images are not available for everywhere. They are often available is urban setting, and less so in forested settings.  With this option available doing spoke canopy spreads - averaging more than two diameters would give a better approximation of actual average crown spread.  We are just beginning to explore the potential of the use of this detailed air photo imagery, and applications like LIDAR.  I am sure it will revolutionize much of what we can accomplish.  Crown spreads are one of parameters that is often undermeasured in the field.  If the images are available it will allow people to measure them from their home computer.  

Similarly GPS coordinates can be pulled from Google Earth if the specific tree can be identified.  I did this for a series of trees I measured in a cemetery.  I made a sketch map of the tree positions while doing the height measurements, and later pulled the GPS coordinates off an air photo of the area.

Ed
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#3)  Re: use Google Earth to accurately measure canopy

Postby Don » Fri Apr 22, 2011 2:05 pm

Steve-
Ed is quite correct.  Unfortunately vast portions of the forested West, and I suspect significant portions of the unpopulated East are without such high resolution imagery as what you have posted.
But for those forested areas of interest with high rez imagery, I can think of no better way of presenting the crown for measurement.  Ed's comment on 'spoking' the crown, and yours at right angles are approximations and get close.  At some point, I believe that the standard may be 'crown area' as measured by a "traverse" around the perimeter of the crown. The 2D area enclosed by the perimeter can be as accurate as the perimeter is drawn, and the most accurate measure of the crown (as is being considered by the AF's intent on crown measure.
Photogrammetry has been around for more than a century...with standards, ethics, substantial body of research already in place.  Much more aerial photography exists than most people realize!
-Don



edfrank wrote:Steve,

This is a excellent idea. This certainly can be used where there is detailed enough imagery to do the measurements.  Such detailed images are not available for everywhere. They are often available is urban setting, and less so in forested settings.  With this option available doing spoke canopy spreads - averaging more than two diameters would give a better approximation of actual average crown spread.  We are just beginning to explore the potential of the use of this detailed air photo imagery, and applications like LIDAR.  I am sure it will revolutionize much of what we can accomplish.  Crown spreads are one of parameters that is often undermeasured in the field.  If the images are available it will allow people to measure them from their home computer.  

Similarly GPS coordinates can be pulled from Google Earth if the specific tree can be identified.  I did this for a series of trees I measured in a cemetery.  I made a sketch map of the tree positions while doing the height measurements, and later pulled the GPS coordinates off an air photo of the area.

Ed
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#4)  Re: use Google Earth to accurately measure canopy

Postby edfrank » Sat Apr 23, 2011 9:28 pm

Don,

you wrote:
But for those forested areas of interest with high rez imagery, I can think of no better way of presenting the crown for measurement.  Ed's comment on 'spoking' the crown, and yours at right angles are approximations and get close.  At some point, I believe that the standard may be 'crown area' as measured by a "traverse" around the perimeter of the crown. The 2D area enclosed by the perimeter can be as accurate as the perimeter is drawn, and the most accurate measure of the crown (as is being considered by the AF's intent on crown measure.
Photogrammetry has been around for more than a century...with standards, ethics, substantial body of research already in place.  Much more aerial photography exists than most people realize!


Yes you can measure the effective diameter by doing a crown area measurement.  the diameter would be 2 x square root(are/pi).  The crown is quite variable in width and extends at different distances at different heights. It has different densities of foliage. They contain gaps and stray sprigs.  Again I must posit the question of whether increased precision of measurement is actually telling you more information about the tree?

I am sure that there has been an enormous body of literature on air photo interpretation and remote sensing.  Twenty years ago I purchased a pair of thick volumes that were an introduction to the subject.  

There are things that have changed from twenty years ago, ad even from five years ago,  Today there is much more detailed imagery available for more areas, and much of it s at your fingertips on the internet.  This was not the case a short time ago.  

In the vast volume of literature and information available we still need to pick out what of that information is of use to us in our current situation.  What applies to what we are doing with trees and what does not?  Is there something in that body of literature that will specifically match our needs?  In some cases, especially for the simplest measures, it might be easier to reinvent the wheel than to sort through what has been done previously.  I look forward to finding useful tools in what has been done before and to developing application that suit our needs now that the detailed information is more widely available and affordable.  The PC's of today give us much more computer power than mainframes of not too long ago.  (And Mac's make better doorstops than ever before.)

Ed

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#5)  Re: use Google Earth to accurately measure canopy

Postby DougBidlack » Sun Apr 24, 2011 12:58 pm

Ed,

I first joined ENTS several years ago for several reasons, but at the top of my list was to be able to measure trees with enough precision to record annual growth.  I measured crown spread using max-min and a whole host of other methods.  I found that the only method that I could repeat three times and come up with the same answer (to the nearest foot) was the spoke method with a minimum of 4 diameter measurements.  Even this method was not good enough for me to get the same measurement every time.  So, do we need a precise measure for crown spread?  I say. Yes!  YES!!!  I also say the same for height and I eagerly await Bob's work on more precise measures of height.  Getting to within a foot when measuring height simply isn't good enough if you want to measure tree growth.

Steve,

I like the idea but I don't think google earth is good enough yet to get measurement to within a foot.  I've planted lots of trees in fields and I wanted them to be within a half foot.  I was able to do this with a 300' fiberglass tape, plastic tent stakes and simple math.  I tried measuring the distances afterwards with google earth and it wasn't good enough.  I also once tried measuring my back deck and it wasn't up to snuff...not yet anyway.  The resolution isn't good enough and I'm not crazy about the measurement tool.  I need to try using it on some trees that I've measured to see how close I get.  Also, since I like to measure every year to determine tree growth, I would need photos for every single year.

Doug
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#6)  Re: use Google Earth to accurately measure canopy

Postby edfrank » Sun Apr 24, 2011 7:38 pm

Doug,

Th problem now is that people do not measure crown spreads because it is too time consuming.  Most of what I have read about Google measurements is that people are praising its accuracy.  How far off were your readings?  As for measuring crown spreads, aside from possible issues with scale, I have my doubts that measuring the crown spread in the field would be more accurate than using Google Maps.  In the field, especially with high branches it is difficult to gauge exactly where the branch tip will project onto the ground. It is very hard to find the position that is directly overhead and if over twenty feet or so, I doubt you are able to obtain a foot level accuracy.  They are at different levels.  So shooting them from the center or from the opposite side of the tree is often impossible.   I think measurements from an air photo overall will give you better crown spread accuracy because you are looking at a flat image.  

The fly in the ointment may be errors in the scale being used by the ruler.  I would suggest that all of the objects, buildings etc. on a close-up image will all have the same actual physical scale.  The scale will not vary from one object to the next in a small area.  I don't think the default scale is that far off and measurements taken using the Google scale are a good approximation and certainly better than not measuring them at all.  I would suggest that If there are two objects, such as the edges of two driveways on the Google map that can be located on the map, the scaling issue can be addressed.  Measure the distance between the two driveways in the field, then measure the distance as it appears on Google Maps.  The ratio for those two differences, could then be used to correct the crown spread information if needed.

Perhaps a stray sprig or two  may not be visible on the Google image, but if they are so few as to not be visible, then they likely are not playing a major role in the tree's existence.  With differences in branch density, leaf density, light capture, crown thickness, and crown shape including these stray sprigs as part of the crown spread is not critical and in fact their inclusion may artificially inflate calculations of such things as crown volume which look at the mass of the crown rather than maximum extent of stray sprigs.  

You may be right, but certainly this process should be more fully considered, and I think it will be a very useful tool for people to use.

Ed

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#7)  Re: use Google Earth to accurately measure canopy

Postby sfischer_16 » Sun Apr 24, 2011 8:22 pm

Guys-

I have been piping up here on this BBS where clearly I am a complete novice playing with giants.

but, still, there is one thing that i wonder if you have addressed.  in software development we have something called "use cases."  a synonymous term might be "scenario."  i am getting a sense that a particular measurement approach can  be best be evaluated in the context in which it will be used, and by whom.  it is clear that there is a world of challenges and subtleties to tree measurement (who knew!).   i wonder if it would help, if you haven't already done it (probably you have, so excuse my ignorance), to formally catalog the use cases for tree measurement, and possibly identify methods most appropriate to them.

apologies in advance if this is off the mark.

steve
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#8)  Re: use Google Earth to accurately measure canopy

Postby edfrank » Sun Apr 24, 2011 8:47 pm

Steve,

You are welcome to post and chime in whenever you want.  Your ideas may be as good and anyone's.  None of us know everything and everyone brings their own knowledge and background to the discussion.  That doesn't mean that we always agree.

Ed
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#9)  Re: use Google Earth to accurately measure canopy

Postby Don » Thu May 05, 2011 3:39 am

Ed/Doug-
While it may not exactly be 'use cases', the suggestion is nearly apt...Doug's measurement accuracy need is much greater than ours (say we're concerned about crown spread).  While it's been decades now since I was around the academics, it seems to me that a large eastern deciduous tree expands and contracts diurnally in the measuring units we're talking about (tenths of a foot), in areas of wide temperature range/wide moisture regime.
Personally, I like the idea of measuring crowns  in terms of square footage as determined by 'traversing' the perimeter of a crown from an aerially obtained image (best at high rez satellite scales) and computing the 'area' (2D). Less of an estimate than the cardinal direction/more than 4 spoke method...: > )
-Don
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#10)  Re: use Google Earth to accurately measure canopy

Postby M.W.Taylor » Sat Jul 02, 2011 7:16 pm

sfischer_16 wrote:I experimented with using Google Earth to measure the canopy of a silver maple.  Google Earth has a measuring tool that is known to be accurate (http://bbs.keyhole.com/ubb/ubbthreads.p ... d=1#import)


Steve,

I have been using GoogleEarth's ruler tool to find big ponderosa pines in the Trinity Alps region for 3 years now. It works great. Typically, any ponderosa, jeffrey or sugar pine with a crown width over 60' is probaby a big pine...

I almost always can isolate the crown. The resolution for most of Trinity Nationa Forest, while not as high res- as metro areas, it sufficient for crown width measurement using the ruler tool.

Trees with big crowns usually have big trunks too.

Michael Taylor

Attached are two images showing that the canopy of this tree is 115' at its widest and 78' at its narrowest.

Seems like this could revolutionize canopy measurement, as it is simple, free, repeatable and verifiable.  With experience ENTS could develop guidelines for correct usage to standardize it as a measuring tool.  (In some settings the outline of the canopy might be hard to detect.)  Note that the image includes GPS coordinates.  

The address I used to search for this tree is 800 Cricket Avenue, 19003.

To download Google Earth, go here:  http://earth.google.com

Give it a try (and verify my measurements)!

(By the way, this silver maple has a girth of 268".  Still need to measure height, which I plan to do by sighting with a carpenter's square held against my cheekbone.)

Steve
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