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SEGMA - parameters

Added by Vandendaele Bastien 5 months ago

Hi all,

I’m creating a script to segment individual crowns from ALS using the implementation of SEGMA within computree.
I’ve seen that there are two methods to filter the detected maxima:
- Filter maxima by neighbourhood (Piboule )
- Filter maximum by exclusion radii (St-Onge)

The second filter needs a parameters file to work but there is no specification on the format of this file.
Is it asking for the number of stratum and there exclusion radii or is it another format?
ex:

Number_of_H_strata 5
Stratum_1 2.0 0.25
Stratum_2 6.0 0.5
Stratum_3 12.0 0.75
Stratum_4 18.0 1.25
Stratum_5 25.0 2.0

Thanks,


Replies (1)

RE: SEGMA - parameters - Added by Piboule Alexandre 5 months ago

Hi,

The file format is the following:
ASCII file.
No header.
2 columns, separated by a tabulation.
- first column : height (in meters)
- second column : corresponding exclusion radius (in meters)

Any number of lines, so you can use:
- either a threshold approach (some threshold heights with corresponding exclusion radii)
- or transcribe an allometric curve with a lot of lines in the file(discrete version of the curve)

here is a fictive example (threshold):
5 1
10 3
15 5
25 7

This case, considering one given apex:
- if apex height is strictly below 5 m, no exclusion radius is applied
- if apex height is in [5 m ; 10 m[, an exclusion radius of 1 m is applied (any other apex below the considered one, and closer than 1 m is eliminated)
- if apex height is in [10 m ; 15 m[, an exclusion radius of 3 m is applied
- if apex height is in [15 m ; 25 m[, an exclusion radius of 5 m is applied
- if apex height is superior or equal to 25 m, an exclusion radius of 7 m is applied

Exclusion radii are applied in 2D.
For this approach, you need to use height point cloud, and not altitude one, where the neighborhood one can work in altitude (if you provide a DTM to the step, only for apex height ordering).

I hope that this answer is complete enough.

Best regards.
Alexandre Piboule.

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