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A diameter tape (D-tape) is a measuring tape used to estimate the diameter of a cylinder object, typically the stem of a tree or pipe. A diameter tape has either metric or imperial measurements reduced by the value of pi. This means the tape measures the diameter of the object. It is assumed that the cylinder object is a perfect circle. The diameter tape provides an approximation of diameter; most commonly used in dendrometry.〔Moran,L.A, and R.A Williams.2002. Comparison of three dendrometers in measuring diameter at breast height. ''Northern Journal of Applied Forestry'' 19:28-33.〕 Diameter tapes are usually made of cloth or metal, and on one side of the tape have diameter measurements and on the other standard measurements (not reduced by pi). ==Use of diameter tapes== Diameter tapes are used to measure tree stems (truck or bole); other parts of trees such as branches and roots; and logs (cut stems). Standard Diameter Height (SDH)〔http://www.sortie-nd.org/help/manuals/help/data/allometry/standard_diam_height.html.〕 is the height at which tree diameter is measured, and is normally called diameter at breast height (DBH). DBH is measured at a fixed height of above the ground in the United States, New Zealand, South Africa, India, and Malaysia; or meters in Australia, Canada, Europe Thailand and Vietnam. DBH is not usually measured at ground level to avoid measuring a tree's butt swell. Butt swell is where the base of the tree is unconventionally thicker than the rest of the tree. Height and diameter are used to determine the volume of a given tree; measuring above the butt swell is required to provide the most accurate measurement. For single-stem trees, DBH is a useful and is easily measured. For multi-stem species such as mallee or other multi-stemmed species, DBH may be inconvenient because of a large number of stems and difficulty of access, and a lower or higher measurement height may be more practical. DBH measurements can be used with other measurements, such as height, to estimate the volume of wood in an individual tree. Usually DBH and height of the trees in a plot or quadrat is measured and used to estimate wood volume for the plot, which can be in turn used to estimate the wood volume in a larger area. DBH measures can be used to calculate basal area. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Diameter tape」の詳細全文を読む スポンサード リンク
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