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Posted to issues@sedona.apache.org by "paleolimbot (via GitHub)" <gi...@apache.org> on 2025/10/26 01:48:47 UTC
[I] Implement ST_Simplify() [sedona-db]
paleolimbot opened a new issue, #244:
URL: https://github.com/apache/sedona-db/issues/244
@joonaspessi kindly did some research on the PostGIS implementation of ST_Simplify(), which is not implemented as a thin wrapper around GEOS:
Actually started the implementation of `ST_Simplify` but noticed that the PostGIS has different behavior for collapsed geometries and collection types in comparison to [GEOS implementation](https://libgeos.org/doxygen/classgeos_1_1simplify_1_1DouglasPeuckerSimplifier.html).
Achieving full PostGIS compatibility (including all the params) would probably require custom Rust implementation.
- Both PostGIS and Sedona-DB uses now GEOS for ST_SimplifyPreserveTopology
- https://github.com/postgis/postgis/blob/master/postgis/lwgeom_geos.c#L935 - Entry point
- https://github.com/postgis/postgis/blob/master/postgis/lwgeom_geos.c#L966 - GEOS function call
- PostGIS uses custom implementation for ST_Simplify
- https://github.com/postgis/postgis/blob/master/postgis/lwgeom_functions_analytic.c#L58 - Entry point
- https://github.com/postgis/postgis/blob/master/liblwgeom/lwgeom.c#L1851 - Core custom implementation
I wonder if the `geo` implementation of Simplify (if it exists) already ticks some of these boxes...since it is a more involved function to implement, it is probably worth going straight for a custom or geo-generic-alg based approach.
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Re: [I] Implement ST_Simplify() [sedona-db]
Posted by "petern48 (via GitHub)" <gi...@apache.org>.
petern48 commented on issue #244:
URL: https://github.com/apache/sedona-db/issues/244#issuecomment-3515299137
> noticed that the PostGIS has different behavior for collapsed geometries and collection types
@joonaspessi Do you happen to still remember some specific test cases that demonstrate these differences? @Abeeujah has kindly taken up this task and is interested in some test cases to help guide the custom implementation.
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Re: [I] Implement ST_Simplify() [sedona-db]
Posted by "paleolimbot (via GitHub)" <gi...@apache.org>.
paleolimbot commented on issue #244:
URL: https://github.com/apache/sedona-db/issues/244#issuecomment-3518423799
> noticed that the PostGIS has different behavior for collapsed geometries and collection types
I took a closer look at the implementation and I think that it is mostly a performance boost rather than changed behaviour. If or when we implement this in Rust we can do something similar...in the meantime we should definitely wire up the rust version!
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Re: [I] Implement ST_Simplify() [sedona-db]
Posted by "Abeeujah (via GitHub)" <gi...@apache.org>.
Abeeujah commented on issue #244:
URL: https://github.com/apache/sedona-db/issues/244#issuecomment-3517670134
This seems to revert the issue with the type change after Simplify
```rust
let geometry = match (initial_type, geometry.geometry_type()) {
(GeometryTypes::MultiPolygon, GeometryTypes::Polygon) => {
Geometry::create_multipolygon(vec![geometry]).map_err(|e| {
DataFusionError::Execution(format!("Failed to revert geometry promotion: {e}"))
})?
}
(GeometryTypes::MultiLineString, GeometryTypes::LineString) => {
Geometry::create_multiline_string(vec![geometry]).map_err(|e| {
DataFusionError::Execution(format!("Failed to revert geometry promotion: {e}"))
})?
}
_ => geometry,
```
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Re: [I] Implement ST_Simplify() [sedona-db]
Posted by "paleolimbot (via GitHub)" <gi...@apache.org>.
paleolimbot closed issue #244: Implement ST_Simplify()
URL: https://github.com/apache/sedona-db/issues/244
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