Generate Seed Points from CHM
This tool aims to generate individual tree seed points from CHM 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.
Navigate to ALS Forest > Segmentation > Generate Seed Points from CHM.
- Input Data: The input file can be a single CHM file or multiple CHM files. The data should be opened in LiDAR360 before being processed.
- Maximum Tree Height (meter)(default value is "80"): The threshold defining the maximum tree height in a study areas. CHM pixels above this threshold will not be considered in the segmentation.
- Minimum Tree Height (meter)(default value is "2"): he threshold defining the minimum tree height in a study areas. CHM pixels below this threshold will not be considered in the segmentation.
- Buffer Size (pix)(default value is "50"): A threshold controls the block size for performing CHM segmentation, which can avoid physical memory overflow. This value should be larger than the maximum crown area and smaller than 1500. If the CHM is larger than 1500 by 1500 pixels, the CHM 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 ID and x, y, z coordinates of each seed points.
- DefaultValue: Restore the default parameters.
Note: Generate Seed by CHM Segmentation function can only be used when the raster data is loaded in the software. Otherwise, the message “There is no raster data!” will pop up. The interface and parameters setting of Generate Seed by CHM are the same as those of CHM Segmentation. The difference between these two tool is that CHM Segmentation will generate a csv file that includes attributes such as tree height, crown diameter and crown area, and a shp file for tree boundary, while Generate Seed by CHM will not generate a shp file. For the seed point file format, refer to Seed Points File.