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Preprocessing observations used for validation

The initial vector file is first used to generate a new vector file containing points at the center of each 10 m Sentinel-2 pixel included in the polygon.

Each new point includes the following attributes :

  • original polygon ID
  • id_pixel: ID of the pixel
  • name_area : Name of the corresponding area (e.g. Sentinel-2 tile ID)
  • epsg: CRS of the associated Sentinel-2 tile as the EPSG integer.

These datapoints are used in the next step to extract Sentinel-2 data more efficiently.

The points generated are kept in the CRS of the original vector file.

Running this step using a script

Run the following instructions to perform this preprocessing step:

from pathlib import Path

from fordead.validation.obs_to_s2_grid import obs_to_s2_grid

output_dir = Path("<MyOutputDirectory>")
input_dir = Path("<MyInputDirectory>/fordead_data")

obs_path = input_dir / "vector/observations_tuto.shp"
sentinel_dir = input_dir / "sentinel_data/validation_tutorial/sentinel_data/"
preprocessed_obs_path = output_dir / "preprocessed_obs_tuto.shp"

    obs_path = obs_path,
    sentinel_dir = sentinel_dir, 
    export_path = preprocessed_obs_path,
    name_column = "id")

NOTE : Set obs_to_s2_grid input variable overwrite = True to re-run this processing stage, otherwise it will raise an error.

Running this step from the command invite

This step can also be ran from the command prompt. The command fordead obs_to_s2_grid -h will print the help information of this step. For example, to use it with the same parameters, the following command can be used:

fordead obs_to_s2_grid --obs_path <MyWorkingDirectory>/vector/observations_tuto.shp --sentinel_dir <MyWorkingDirectory>/sentinel_data/validation_tutorial/sentinel_data/ --export_path <MyWorkingDirectory>/vector/preprocessed_obs_tuto.shp --name_column id


The vector file containing only points is written in the following file: fordead_data/vector/preprocessed_obs_tuto.shp

Observations outside of the footprint of the Sentinel-2 data are removed from the resulting vector and their ID printed in the command prompt.

The following figure shows a zoomed view on observation 7 and corresponding attribute table.


NOTE : If the initial vector file contains points, their locations are preserved and their id_pixel attribute is set to 1.