Generate Seeds from Layer Stacking

Summary

This tool aims to generate individual tree seed points using an layer stacking algorithm so that they can be used for Point Cloud Segmentation based on Seeds. The ALS Editor tool can be used to edit the seed points and therefore improve the individual tree segmentation accuracy.

Usage

Navigate to ALS Forest > Segmentation > Generate Seeds from Layer Stacking.

Settings

• Input Data: Ensure that each input point cloud data is Normalize by DEM or Normalize by Ground Points. The input file can be a single file or multiple data files. Point cloud data should be opened in LiDAR360 before being processed.
• XSize (meter)(default value is "1"): Grid x-axis resolution. It is recommended to set this parameter between 0.3m and 2m.
• YSize (meter)(default value is "1"): Grid y-axis resolution, It is recommended to set this parameter between 0.3m and 2m.
• Height Above Ground (meter)(default value is "2"): Usually, it is desirable to ignore points below a particular height to avoid influence low vegetations (e.g., grass and shrub). Points below this threshold will not be considered in the segmentation. A value of 2 m is commonly used.
• Layer Thickness (meter)(default value is "1"): The layer thickness is used to cut the layer for stacking. It is recommended to set this parameter between 0.5m and 2m.
• Minimum Spacing Between Trees (meter)(default value is "1"): This parameter should be set as the minimum spacing of the tree. This parameter can be adjusted to avoid over- or under-segmentation.
• Buffer Size (pix)(default value is "50"): A threshold controls the block size for performing segmentation, which can avoid physical memory overflow. This value should be larger than the maximum crown area and smaller than 1500. If the image is larger than 1500 by 1500 pixels, it will be forced to divided into a number of blocks with a size of 1500 by 1500 pixels.
• Gaussian Smooth (optional): This parameter is to control whether to perform Gaussian smoothing. In general, it is recommended to check the Gaussian smoothing option to remove noise effects.
• Sigma (default value is "1"): Gaussian smoothing factor. The greater the value is, the smoother the results are. The degree of smoothness can affect the number of trees being segmented. In the case of under-segmentation, it is recommended to reduce this value (e.g. 0.5); and in the case of over-segmentation, it is recommended to increase the value (e.g. 1.5).
• Radius (pix)(default value is "5"): The window size used by Gaussian smoothing, which should be an odd number. Generally, it can be set to the average crown diameter.
• Output Path: Path of the output file. The resultant product is a comma-separated table in “csv” format which contains the ID and x, y, z coordinates of each seed points.
• DefaultValue: Restore the default parameters.

Note: Only when the point cloud data is loaded in the software can you use the Generate Seed by Layer Stacking function; otherwise, the message "There is no point cloud data meeting the conditions of calculation!" will pop up. If the maximum Z value of the point cloud is greater than 200 m or the maximum Z minus the minimum Z is greater than 200 m, the data is not considered to have been normalized, and the prompt information shown in the figure below will pop up. Click “YES” to keep using this type of data in the operation; otherwise, click "NO" and reselect the input data file. The seed point file obtained by layer stacking is the same as the seed point file generated by CHM, please refer to Seed Points File.