Thanks to John for the photographs and measurements of Redwoods in Hatchford Woods in Ockham, Surrey. John measured some of the trees with a clinometer and also using the photograph method.
He says, "I think one needs to practice on a known structure on level ground first.
Trouble is finding something in the right locations with a known height."
The photographic method is less reliable the closer you are to the tree and the more the tree fills the available image size, the former because of the problem of perspective, the latter because of lens distortion on wide-angle setting. This would explain the trees that measured much smaller using the photographic method than using the clinometer, but of course some of your photographed measured trees are listed as larger than the clinometer measurements! I'm not sure what to make of that, except to say that this shows how tricky it is to measure trees when they are crowded amongst other trees. Thanks again for all the information. |
