PostGIS Internals

These notes cover implementation details that are useful when working inside PostGIS rather than only using the SQL API.

• Memory management covers allocator boundaries and ownership rules.
• PostgreSQL internals for PostGIS developers covers PostgreSQL C function macros, varlena detoasting, serialized geometry handling, and a typical SQL function flow.

• Empty geometry semantics covers how EMPTY differs from SQL NULL, how empties are serialized and indexed, and how accessors, measurements, predicates, and collections handle empty inputs.
• Spatial collections and raster/vector crossings covers current geometry collection handling and explains how the retired raster/vector spatial-collection abstraction relates to current code.
• 2D and 3D distance internals covers how geometry distance functions dispatch 2D and 3D candidate checks, including segment-segment and surface cases.
• Precision and tolerance internals maps the current GEOS grid-size, snap-tolerance, topology-precision, and MVT quantization surfaces.

• Raster affine georeferencing covers the scale, skew, rotation, and upper-left coefficients used to convert raster cell coordinates into spatial coordinates.
• Raster physical georeferencing parameters covers the reverse calculation from stored affine coefficients back to pixel sizes, rotation, and basis-vector separation.
• Raster storage and WKB covers the current PostgreSQL varlena representation, Raster WKB/HexWKB paths, out-db band storage, and raster catalog contracts.
• PostGIS Raster and the GDAL driver records the boundary between PostGIS-maintained raster storage/catalog behavior and the external GDAL PostGISRaster driver.

• Topology internals covers internal topology implementation helpers such as edge end stars.