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Level 1C absolute geometric disparity metrics

Introduction​

This metadata file summarises the comparison between a specific band of processed image and a reference image.

Tiepoints are collected for both of these images.

Corresponding tiepoints are collected between the reference and processed images. The distances between these corresponding tiepoints are measured.

note

These tiepoints are independent of the tiepoints collected to process the image

Sample file​

Sample: LANDSAT-9_OLI_20220804T083603_20220804T083634_L1C_R1C1_GVER_ABS.json

Property details​

This section contains explanations on specific properties of the absolute geometric disparity metrics file. All the properties that have been expanded on are listed in a structured manner under the Reference section.

Pixel colour mappings​

This section describes the pixelColorMappings property. This provides a legend to quantify disparities in colour ranges. This legend is used for the thumbnail referenced in imageName.

Measurements​

Each absolute geometric disparity metadata file contains a measurements section. This section is an array of measurements taken against a reference dataset, and contains:

  • id: The band-ID being measured
  • refBand: A formatted string describing the reference band used for the measurement (e.g., "Band 4 (red)")
  • refResolution: An array with across- and along-track resolutions for the reference band
  • refSpacecraft: The name of the reference spacecraft being used (e.g., "Sentinel-2")
  • imageName: The filename of the preview image being generated containing a visual representation of the results of the geometric verification
  • disparitiesXYInMeters: A 2-dimensional array containing a set of disparity measurements (see below)
  • coordLonLat: A 2-dimensional array containing the coordinates of each disparity measurements (see below)
  • coverage: A percentage (out of 100) showing how much of the scene is covered by the geometric verification results

The combination of disparitiesXYInMeters and coordLonLat can be used to generate a map of each disparity point. The coordinates, in the sequence [longitude, latitude] denotes where the measurement was taken. The disparities is expressed in meters as the distance away from the coordinate point in the sequence [longitude, latitude].

Reference: absolute geometric disparity metrics​

The following reference describes the content of the absolute geometric disparity metrics file.

  • measurements (array): A list of disparity metrics grouped by individual bands.
    • Items (object)
      • coordsLonLat (array): The (longitude, latitude) coordinates of the evaluated tie-points.
        • Items (array)
          • Items (number, format: double)
      • disparitiesXYInMeters (array): A list of (x,y) disparities of the evaluated tie-points (in meters).
        • Items (array)
          • Items (number, format: double)
      • id (string)
      • imageName (string): An illustration of the quality of all the tie-points evaluated on the image.
      • refBand (string): The band ID of the reference image being used during comparison.
      • refResolution (array): The resolution of the reference image used during comparison.
        • Items (number, format: double)
      • refSpacecraft (string): The Spacecraft ID of the associated reference image.
  • pixelColorMappings (string): Mappings used to quantify disparities in color ranges (only for display purposes).