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| Here are some tips on how to measure the Girth and Height of trees. Remember that it is important to make a note of the date that you measure, and feel free to contact us if you would like us to include a record of your findings and/or measurements of Redwood Trees, (preferably with photographs). |
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Use a soft, preferably plastic, tape measure and, taking care not to damage the bark, wrap it around the tree 1.5 metres from ground (around chest height, but refer to chart).
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A camera is needed to attempt this method of measuring the height of a tree. You will need to place the camera a good distance away from the tree on a tripod or some other suitable object. Set the camera to timer mode and run back to the tree!
Standing to one side, hold a steel tape measure extended up 2 metres ensuring that the bottom of the measure is level with the bottom of the tree. (3 metres would be better but the tape may buckle and fall).
The camera needs to be placed a long way back from the tree for the most accurate measurement; ideally at least twice the height of the tree. Any closer and "perspective" error will become significant - do a scale drawing as an example and you will see what we mean. Also, remember to include the top of the tree - it's easy to miss this when setting up the camera. |
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At your computer, use the selection tool in a photo manipulation package (unfortunately Paint will not do) to select and copy a small rectangle including the exact length of the measure. |
Paste the image of the measure as many times as necessary all the way up the tree (see picture on left) and then you can calculate the height. Though this sounds a little Heath-Robinson, this method should be able to produce fairly reasonable (if not scientific) results. We are, however, relying on the linearity of the lens and most will introduce a varying degree of distortion to the image, particularly when zoom cameras are used in their wide-angle setting.
| In other words, a 1m rule at the edge of a photograph may well appear to be a slightly different length than one at the centre. |
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| There are several things that can be done to minimise the inaccuracy due to these effects. Avoid using the wide-angle setting on zoom cameras - try to use a degree of telephoto setting. Happily, this coincides with the need to be a long way back to minimise perspective errors! Finally, avoid using the outer 15% or so of the image. Obviously all these factors are inter-dependant. |
Clinometer! Since buying a clinometer, our method of measuring trees has changed.
You can find a lot of information about using Clinometers on the Internet. |
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Briefly, you stand at a point as far from the centre of the trunk of the tree as its estimated height, so that the elevation angle is somewhere around 45°, this gives the best "geometry." Measure the distance (D) from the tree with a tape. Then stand at the mark and sight the top of the tree, finding its elevation angle  . The height (H) of the tree is then:
H = D tan + HI |
| (HI is the measurement from the ground to your eye). See the diagram. |
You could do all the above maths if you are feeling a little masochistic but the good news is: you don't have to!
All you need do is set your clinometer to 45° then walk back until your sight is aligned with the top of the tree, taking care not to fall into any ponds in the process. Mark the point in the ground at which you are standing and then set your clinometer to 0°. Now find the point on the trunk of the tree which is aligned with your sight; this will be the point that is level with your head. Now simply measure the distance from your mark in the ground to the tree and add to this the height from the ground to the 0° point on the trunk of the tree. Hey presto! Height found with no maths apart from a simple addition. |
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There is another type of clinometer with which you simply measure to a predetermined distance from the base of the tree, aim to the top and adjust the rotary part. A scale is then provided which gives the distance reading directly. A reasonable quality model like this tends to be rather expensive, feels like cheating  and is probably not as accurate as a comparable quality standard type clinometer. |
Do you have any other methods of measuring trees? |
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