# util_makeZhangParam

##### Parameters for progressive morphological filter

The function lasground with the progressive morphological filter allows for any sequence of parameters. This function enables computation of the sequences using equations (4), (5) and (7) from Zhang et al. (see reference and details).

##### Usage

```
util_makeZhangParam(b = 2, dh0 = 0.5, dhmax = 3, s = 1, max_ws = 20,
exp = FALSE)
```

##### Arguments

- b
numeric. This is the parameter \(b\) in Zhang et al. (2003) (eq. 4 and 5).

- dh0
numeric. This is \(dh_0\) in Zhang et al. (2003) (eq. 7).

- dhmax
numeric. This is \(dh_{max}\) in Zhang et al. (2003) (eq. 7).

- s
numeric. This is \(s\) in Zhang et al. (2003) (eq. 7).

- max_ws
numeric. Maximum window size to be used in filtering ground returns. This limits the number of windows created.

- exp
logical. The window size can be increased linearly or exponentially (eq. 4 or 5).

##### Details

In the original paper the windows size sequence is given by eq. 4 or 5:

\(w_k = 2kb + 1\) or \(w_k = 2b^k + 1\)

In the original paper the threshold sequence is given by eq. 7: \(th_k = s*(w_k - w_{k-1})*c + th_0\) Because the function lasground applies the morphological operation at the point cloud level the parameter \(c\) is set to 1 and cannot be modified.

##### Value

A list with two components, the windows size sequence and the threshold sequence.

##### References

Zhang, K., Chen, S. C., Whitman, D., Shyu, M. L., Yan, J., & Zhang, C. (2003). A progressive morphological filter for removing nonground measurements from airborne LIDAR data. IEEE Transactions on Geoscience and Remote Sensing, 41(4 PART I), 872<U+2013>882. http:#doi.org/10.1109/TGRS.2003.810682.

*Documentation reproduced from package lidR, version 1.4.2, License: GPL-3*