Point sampling on raster

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First phase: systematic sampling

  1. Click Plugins --> Manage and Install Plugins.
  2. Type in the search bar Point sampling tool, click on the plugin name and then on Install plugin.
  3. Load the single band raster file C_ID.tif created by Convert vector to raster.
  4. Load the regular grid as vector point file systematic_grid100.shp' created by Creating regular grid.
  5. Make sure that both layers are ticked in the TOC.
  6. Open the Point Sampling Tool clicking Qgis psample button.png.
  7. Select the layer containing sampling points.
  8. Specify the output of the resulting vector file marking column with CTRL + left click.
  9. Enter an output shapefile name systematic_grid100_cid.shp and path by clicking Browse.
  10. Confirm with OK. The new layer is added to the Layer Panel .

Qgis point sample.png

Second phase: stratified random sampling with equal allocation

  • In the search engine of the Processing Toolbox, type Random selection and select Random selection within subsets under Vector selection tools of QGIS.
  • Select the regular point grid (result of Creating regular grid) as the input layer.
  • Select the Column name containing the grouping class code as ID field.
  • Enter 10 as sample size for each category.
  • Click Run to execute the algorithm.
  • Mark the the regular point grid in the TOC. Right click, Save as....
  • Format of the output vector file is ESRI Shapefile
  • Do not forget to tick Save only selected features.
  • Define directory and output file name.
  • Click Run to save the file.

Qgis vector saveas2.png

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