The function classify_ground 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).

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

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).

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

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 classify_ground applies the morphological operation at the point cloud level the parameter \(c\) is set to 1 and cannot be modified.

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.

```
# NOT RUN {
p = util_makeZhangParam()
# }
```

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