Individual Tree Detection (ITC)
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=Extracting tree heights= | =Extracting tree heights= | ||
− | We extract normalized | + | We extract normalized heights from the original CHM using the QGIS point sampling plugin. |
+ | # Click {{mitem|text=Plugins --> Manage and Install Plugins}}. | ||
+ | # Type in the search bar {{typed|text=Point sampling tool}}, click on the plugin name and then on {{button|text=Install plugin}}. | ||
+ | # Load the single band raster file ''chm.tif''. | ||
+ | # Load the vector point file ''Seed points.shp'''. | ||
+ | # Make sure that both layers are ticked in the [[TOC]]. | ||
+ | # Open the '''Point Sampling Tool''' clicking [[File:Qgis_psample_button.png]]. | ||
+ | # Specify the output of the resulting vector file marking column with '''CTRL + left click'''. | ||
+ | # Enter an output shapefile name ''see_points_chm.shp'' and path by clicking {{button|text=Browse}}. | ||
+ | # Confirm with {{button|text=OK}}. The new layer is added to the Layer Panel . | ||
+ | [[File:Qgis_point_sample2.png|400px]] | ||
=Generate a seed grid= | =Generate a seed grid= |
Revision as of 23:59, 6 January 2018
Contents |
Filter the CHM derived from LiDAR data
We use a Canopy Height Model (CHM) derived from LiDAR data as decribed here to detect Individual Tree Crowns (ITC). Two preprocessing steps prepare a watershed segmentation approach: (1) Gaussian filtering and (2) inversion of a CHM.
- In the search engine of the Processing Toolbox, type smooth and select Smoothing (gaussian) under Image filtering of the Orfeo Toolbox.
- Select the CHM raster data file in GeoTiff format as input layer.
- The smoothing type is gaussian.
- The circular structuring element has a radius of 2 pixels.
- Enter name and path for an output file.
- Click on Run.
Invert the CHM
Now the smoothed CHM will be inverted.
- In the search engine of the Processing Toolbox, type invert and select Invert grid under Raster tools of SAGA.
- Select the smoothed CHM raster data file from previous step as input layer.
- Enter name and path for an output file.
- Click on Run.
Watershed segmentation
- In the search engine of the Processing Toolbox, type watershed and select Watershed segementation under Image Analysis of SAGA.
- Select the inverted and smoothed CHM raster data file as input Grid.
- The Output is Segment ID
- Select as Method the flow accumulation of Minima
- Seed points: enter name and path for a vector point output file.
- Click on Run.
Extracting tree heights
We extract normalized heights from the original CHM using the QGIS point sampling plugin.
- Click Plugins --> Manage and Install Plugins.
- Type in the search bar Point sampling tool, click on the plugin name and then on Install plugin.
- Load the single band raster file chm.tif.
- Load the vector point file Seed points.shp'.
- Make sure that both layers are ticked in the TOC.
- Open the Point Sampling Tool clicking .
- Specify the output of the resulting vector file marking column with CTRL + left click.
- Enter an output shapefile name see_points_chm.shp and path by clicking Browse.
- Confirm with OK. The new layer is added to the Layer Panel .