GitHub

Grid Extension Specification

This document explains the Grid Extension to the SpatioTemporal Asset Catalog (STAC) specification.

The purpose of the Grid Extension is to provide fields related to gridded data products.

There are two main uses of the grid:code field defined in this specification. Both are primarily for use in supporting a path for a user exploring a dataset from a UI where there are too many results to display individually, where the user must first be presented with summary / aggregated data, and then drill down to individual items.

The first is that it allows for precise aggregation in a STAC API implementation of Items that cover the same grid area. The STAC API Aggregation Extension is a work-in-progress, but will eventually support aggregating over this field.

The second aspect is that it helps for display to a user when a gridded dataset has Items that have slightly different footprints for Items over the same grid square. For example, Landsat 8 scenes for the same path/row grid square are often off by a few pixels from each other, which makes them not match exactly. Some products with grids that are significantly different from EPSG:4326 have footprints that are far from a square after reprojection, such how MODIS sinusoidal grid squares become increasingly curved as they move away from the equator and meridan. This can make the GeoJSON Polygon large, as more points must be added to maintain an accurate reprojected shape. With a grid code defined for an Item, a UI could have a pre-determined geometry at a reasonable resolution for that grid square, and display it once for each all the Items in that grid square.

Item Properties Fields

Field Name Type Description
grid:code string REQUIRED. The identifier for the grid element associated with the Item.

Additional Field Information

grid:code

The field grid:code defines a unique value for each grid square in a gridding. The code will be of the form {grid designation}-{grid square code}, where the grid designation is a short alphanumeric code for the grid (e.g., MGRS) and code is a short encoded value for a specific grid square. The encoded value for the square should consist of uppercase alphanumeric characters, underscore (_) (preferred separator), or minus sign (-).

The grid code values below are recommended for these products. Implementers may also devise proprietary systems for their own griddings.

Military Grid Reference System (MGRS)

  • Format String: MGRS-{grid zone designator}{latitude band}{square}
  • Examples: MGRS-35NKA, MGRS-35NKA1234, MGRS-35NKA123456, MGRS-35NKA12345678, MGRS-35NKA1234567890
  • Components:
    • grid zone designator: UTM grid zone
    • latitude band: latitude band, lettered C-X (omitting the letters "I" and "O")
    • square: a pair of letters designating one of the 100km side grid squares within the grid zone and latitude band square, and optionally either 2, 4, 6, 8, or 10 additional digits
  • Products: Sentinel-2
  • Reference: https://en.wikipedia.org/wiki/Military_Grid_Reference_System
  • Related Extensions: https://github.com/stac-extensions/mgrs

MODIS Sinusoidal Tile Grid

  • Format String: MSIN-{horizontal}{vertical}
  • Example: MSIN-2506
  • Components:
    • horizontal: horizontal tile number
    • vertical: vertical tile number
  • Products: many MODIS products, including MCD43A4, MxD11A1, and MxD13A1
  • Reference: https://modis-land.gsfc.nasa.gov/MODLAND_grid.html

Worldwide Reference System (WRS-1)

Worldwide Reference System (WRS-2)

Digital Orthophoto Quadrangle

Represents one U.S. Geological Survey (USGS) 7.5-minute quadrangle. The names are based on that of the 7.5-minute quad.

Digital Orthophoto Quarter Quadrangle

Represents one U.S. Geological Survey (USGS) 7.5-minute quadrangle. The Digital Orthophoto Quarter Quadrangle (DOQQ) represents one quarter of the quadrangle. The names are based on that of the 7.5-minute quad, followed by NE, NW, SW, or SE for the DOQQ.

Maxar ARD Tile Grid

  • Format String: MXRA-Z{zone}-{quadkey}
  • Example: MXRA-Z14-120200003323
  • Components:
    • zone: UTM zone
    • quadkey: 12-digit quadkey identifier
  • Products: Maxar ARD images and derivatives
  • Reference: Maxar ARD Documentation

EASE-DGGS

  • Format String: EASE-DGGS-L{level}.{row-column for each level}
  • Example: EASE-DGGS-L0.405963, EASE-DGGS-L6.405963.33.22.22.99.99.99
  • Components:
    • level: Grid refinement level. Ranges from 0 to 6 with 6 being the most granular level.
    • row-column for each level: Grid cell row-column for each level in ascending level order (level 0 first), separated by ".".
  • Products: unknown
  • Reference: https://www.tandfonline.com/doi/pdf/10.1080/20964471.2021.2017539

Copernicus Digital Elevation Model Grid

  • Format String: CDEM-{northing}{easting}
  • Example: CDEM-S90W178
  • Components:
    • northing: latitude coordinate in decimal degrees without the decimal _00 part, e.g., S50.
    • easting: longitude coordinate in decimal degrees without the decimal _00 part, e.g., W125.
  • Products: Copernicus DEM GLO-30, GLO-90, and EEA-10 products in DGED format
  • Reference: Copernicus DEM Product Handbook

EEA Reference Grid

  • Format String: EEA-{resolution}{easting}{northing}
  • Example: EEA-100kmE31N36
  • Components:
    • resolution: Recommended grid resolutions are 100m, 1km, 10km and 100km. Alternatively, 25m or 250m resolution can be used for analysis purposes, where the standard 100m or 1km grid cell size is not appropriate. The resolution is denoted in meter (m) for cell sizes below 1000 meters and kilometre (km) for cell sizes from 1000 meters and above.
    • northing and easting: Reflects the distance of the lower left grid cell corner from the false origin of the CRS. In order to reduce the length of the string, Easting (E) and Northing (N) values are divided by

Read the original on github.com ↗