fix: Allow simplifying geometries in OGC Tiles API

CHANGES.md

@@ -8,6 +8,9 @@ Note: Minor version `0.X.0` update might break the API, It's recommended to pin
 
 ## [unreleased]
 
+* fix geometry simplification on OGC Tiles endpoints (author @guillemc23, https://github.com/developmentseed/tipg/pull/249)
+
+
 ## [1.3.0] - 2025-11-17
 
 * switch to official python docker image from `bitnami`

tipg/collections.py

@@ -411,10 +411,19 @@ def _select_mvt(
         geometry_column: Column,
         tms: TileMatrixSet,
         tile: Tile,
+        simplify: Optional[float],
+        preserve_topology: Optional[bool],
     ):
         """Create MVT from intersecting geometries."""
         geom = pg_funcs.cast(logic.V(geometry_column.name), "geometry")
 
+        if simplify:
+            geom = logic.Func(
+                "ST_SnapToGrid",
+                logic.Func("ST_SimplifyPreserveTopology" if preserve_topology else "ST_Simplify", geom, simplify),
+                simplify,
+            )
+
         # make sure the geometries do not overflow the TMS bbox
         if not tms.is_valid(tile):
             geom = logic.Func(
@@ -866,6 +875,8 @@ async def get_tile(
         geom: Optional[str] = None,
         dt: Optional[str] = None,
         limit: Optional[int] = None,
+        simplify: Optional[float] = None,
+        preserve_topology: Optional[bool] = None,
     ):
         """Build query to get Vector Tile."""
         limit = limit or mvt_settings.max_features_per_tile
@@ -885,6 +896,8 @@ async def get_tile(
                 geometry_column=geometry_column,
                 tms=tms,
                 tile=tile,
+                simplify=simplify,
+                preserve_topology=preserve_topology,
             ),
             self._from(function_parameters),
             self._where(

tipg/factory.py

@@ -1668,6 +1668,18 @@ async def collection_get_tile(
                     description="Limits the number of features in the response. Defaults to 10000 or TIPG_MAX_FEATURES_PER_TILE environment variable."
                 ),
             ] = None,
+            simplify: Annotated[
+                Optional[float],
+                Query(
+                    description="Simplify the output geometry to given threshold in the units of the output CRS.",
+                ),
+            ] = None,
+            preserve_topology: Annotated[
+                Optional[bool],
+                Query(
+                    description="Whether to preserve the same topology as the original data when simplifying.",
+                ),
+            ] = None,
         ):
             """Return Vector Tile."""
             tms = self.supported_tms.get(tileMatrixSetId)
@@ -1688,6 +1700,8 @@ async def collection_get_tile(
                     limit=limit,
                     geom=geom_column,
                     dt=datetime_column,
+                    simplify=simplify,
+                    preserve_topology=preserve_topology,
                 )
 
             return Response(tile, media_type=MediaType.mvt.value)