DSL geom functions

The GISPulse DSL exposes a small whitelist of geometry functions you can call from your triggers.yaml. Each function compiles down to a DuckDB spatial expression, runs against the dataset's geometry column, and returns a typed value usable in set_field or validate: rules.

The compiler never executes user-supplied Python — expressions are parsed via Python's ast module and rejected unless every node fits the strict allowlist. See the SQL dialect contract for the dispatch rules and docs/adr/0001-dsl-sql-dialect.md for the AST allow-list rationale.

Dialecte SQL : ces fonctions compilent vers DuckDB-spatial par construction (4-arg ST_Transform). Voir Contrat de dialecte SQL pour les détails sur la portabilité PostGIS / SpatiaLite et le mécanisme d'override engine:.

Quick reference

Function	Returns	CRS-aware	Default epsg=	DuckDB call
geom_area_m2()	double (m²)	yes	EPSG:2154	ST_Area(ST_Transform(geom, src, target, true))
geom_perimeter_m()	double (m)	yes	EPSG:2154	ST_Perimeter(...)
geom_length_m()	double (m)	yes	EPSG:2154	ST_Length(...)
geom_centroid_x()	double	yes	EPSG:2154	ST_X(ST_Transform(ST_Centroid(geom), …))
geom_centroid_y()	double	yes	EPSG:2154	ST_Y(ST_Transform(ST_Centroid(geom), …))
geom_npoints()	integer	no	—	ST_NPoints(geom)
geom_is_valid()	boolean	no	—	ST_IsValid(geom)

Examples

Auto-fill the surface in hectares

version: 1
gpkg: ./data/parcels.gpkg
triggers:
  - name: parcels_set_surface
    table: parcels
    when: [INSERT, UPDATE_GEOM]
    actions:
      - type: set_field
        field: surface_ha
        value: "geom_area_m2() / 10000"

The compiler emits the SQL fragment (ST_Area(ST_Transform("geom", 'EPSG:4326', 'EPSG:2154', true)) / 10000), which DuckDB pushes down on the underlying GeoPackage.

Tag invalid geometries

version: 1
gpkg: ./data/parcels.gpkg
validate:
  - id: shape_valid
    rule: "geom_is_valid()"
    mode: tag
    tag_field: validation_status
    message: "Geometry self-intersects"

Failing rows are tagged with validation_status = 'failed:shape_valid' without touching the rest of the row.

Override the metric CRS per call

- type: set_field
  field: distance_to_origin_m
  value: "geom_centroid_x(epsg='EPSG:3857')"

CRS handling

Measure functions (geom_area_m2, geom_perimeter_m, geom_length_m) project the geometry to a metric CRS before calling DuckDB's ST_Area / ST_Perimeter / ST_Length. The default target is EPSG:2154 (Lambert 93) — the right pick for FR cadastre / topo data. Override per-call with epsg='EPSG:NNNN', or change the per-dataset default in your trigger runtime configuration.

The dataset's source CRS is never inferred from the file. The runtime reads it from the GeoPackage's gpkg_geometry_columns.srs_id (or the PostGIS geometry_columns row); you pass it through to the compiler via CompilationContext.source_epsg.

Allowed expression grammar

Inside a set_field value or a validate: rule: you may write:

• Integer / float / boolean literals (50, 1.2, True).
• Column references — bare identifiers like price, tax_rate. Names must match [A-Za-z_][A-Za-z0-9_]{0,62} and SQL reserved words are rejected (SELECT, FROM, …).
• Arithmetic: + - * / % plus parentheses.
• Calls to whitelisted geom functions only (the seven above). Bare references to a function name are rejected — call them with ().
• Inside validate: rules, also: comparisons (== != < <= >>=) and boolean ops (and, or, not).

Everything else is rejected at config-load time:

• Method calls (geom.area()), attribute access (row.x), indexing (a[0]), slicing.
• Lambdas, comprehensions, f-strings, list/dict/set literals.
• __import__, eval, globals, any function not on the whitelist.
• The ** exponent (use repeated multiplication if you really need it).

This is by design: the parser exists to give you derived columns and declarative validation, not a sandbox for arbitrary computation. If you need that, use a run_sql action with a hand-written SQL statement that lives under your security review.