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## DBH extraction method

Added by Tremblay Jean-François over 3 years ago

Bonjour à tous,

I have a question about the ONF plugin, specifically the DBH estimation.

I know that you guys fit multiple cylinders around breast height and then use these cylinders to estimate DBH.

I just wanted to know: do you use the mean of the diameters of cylinders around breast height, or do you use the median?

Also, Jan, in SimpleTree, what do you use to estimate the DBH?

Thank you very much!

### Replies (1)

#### RE: DBH extraction method - Added by Piboule Alexandre over 3 years ago

Hi,

The ONF_StepExtractDiameterFromCylinders step takes the following parameters:

- Href: reference height (1.30 m)

- Hmin: minimum height

- Hmax : maximum height

- NbMinCylinders: minimum number of cylinders to adjust a circle

- DeltaMax : maximum taper

The step takes into account all cylinders between Hmin and Hmax.

1) If there are less than NbMinCylinders, no circle is extracted.

2) Otherwise:

A graph (Cylinder diameter) = f(Height) is “created” with one point per cylinder taken into account.

A line is adjusted (linear regression).

The diameter is estimated (diameter value) using the line adjusted by taking X = Href.

The slope of the line is compared to DeltaMax. If the slope is greater than DeltaMax, the circle is not kept. (it is possible to disable this filter by setting a very high value in this parameter).

Sincerely.

Alexandre.