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DGGRID

DGGRID is the core C++ library and command-line tool that implements IGEO7. All other IGEO7 tools ultimately call DGGRID for grid generation and coordinate conversion.

What DGGRID Does​

DGGRID is a general-purpose DGGS engine supporting dozens of grid types (ISEA3H, ISEA4H, ISEA7H, FULLER7H, and many more). For IGEO7, the relevant type is IGEO7 (or equivalently ISEA7H with Z7 addressing).

Key operations:

  • Generate cell polygons for an extent or global grid
  • Convert lat/lng coordinates to cell IDs
  • Convert cell IDs to lat/lng centroids or cell polygons
  • Generate grid statistics (cell count, area, CLS per resolution)
  • Transform between addressing schemes (Z7, Z7_STRING, SEQNUM, Q2DI, PROJTRI)

Installation​

See Installation for build instructions.

# Quick check
dggrid --version

How It Works​

DGGRID is driven by metafiles — plain-text configuration files that specify the operation, DGGS type, resolution, and I/O paths. dggrid4py generates these metafiles automatically.

A minimal metafile for generating IGEO7 cells looks like:

dggrid_operation  GENERATE_GRID
dggs_type         IGEO7
dggs_res_spec     9
clip_subset_type  WHOLE_EARTH
cell_output_type  GEOJSON
cell_output_file_name  /tmp/igeo7_res9

Run with:

dggrid igeo7_res9.meta

DGGS Type: IGEO7 vs ISEA7H​

DGGRID supports two names for the same underlying grid:

Type stringAddressingNotes
IGEO7Z7 / Z7_STRINGRecommended; uses Z7 indexing natively
ISEA7HSEQNUM, Q2DI, etc.Same grid; older addressing schemes

Always use IGEO7 with output_address_type="Z7_STRING" for new work.

ISEA Orientation​

DGGRID uses the standard ISEA orientation for IGEO7:

dggs_vert0_lon     11.25
dggs_vert0_lat     58.2825255885
dggs_vert0_azimuth  0.0

This is the default and does not need to be specified explicitly when using dggrid4py.

Further Reading​

  • dggrid4py — Python wrapper
  • Installation — build instructions
  • DGGRID manual: included in the DGGRID repository as dggridManual.pdf