R: Parameters for progressive morphological filter

util_makeZhangParam {lidR} | R Documentation

## Parameters for progressive morphological filter

### Description

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).

### 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 classify_ground 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), 872–882. http:#doi.org/10.1109/TGRS.2003.810682.

### Examples

    p = util_makeZhangParam()

[Package lidR version 3.2.2 Index]