BlakeOrth commented on code in PR #8943: URL: https://github.com/apache/arrow-rs/pull/8943#discussion_r2594188950
########## parquet-geospatial/src/types.rs: ########## @@ -0,0 +1,394 @@ +// Licensed to the Apache Software Foundation (ASF) under one +// or more contributor license agreements. See the NOTICE file +// distributed with this work for additional information +// regarding copyright ownership. The ASF licenses this file +// to you under the Apache License, Version 2.0 (the +// "License"); you may not use this file except in compliance +// with the License. You may obtain a copy of the License at +// +// http://www.apache.org/licenses/LICENSE-2.0 +// +// Unless required by applicable law or agreed to in writing, +// software distributed under the License is distributed on an +// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY +// KIND, either express or implied. See the License for the +// specific language governing permissions and limitations +// under the License. + +use arrow_schema::{ArrowError, DataType, extension::ExtensionType}; +use serde::{Deserialize, Serialize}; + +/// Hints at the likely Parquet geospatial logical type represented by a [`Metadata`]. +/// +/// Based on the `algorithm` field: +/// - [`Hint::Geometry`]: WKB format with linear/planar edge interpolation +/// - [`Hint::Geography`]: WKB format with explicit non-linear/non-planar edge interpolation +/// +/// See the [Parquet Geospatial specification](https://github.com/apache/parquet-format/blob/master/Geospatial.md) +/// for more details. +#[derive(Copy, Clone, Debug, Serialize, Deserialize)] +pub enum Hint { + /// Geospatial features in WKB format with linear/planar edge interpolation + Geometry, + /// Geospatial features in WKB format with explicit non-linear/non-planar edge interpolation + Geography, +} + +/// The metadata associated with a [`WkbType`]. +#[derive(Clone, Debug, Default, Serialize, Deserialize)] +pub struct Metadata { + /// The Coordinate Reference System (CRS) of the [`WkbType`], if present. + /// + /// This may be a raw string value (e.g., "EPSG:3857") or a JSON object (e.g., PROJJSON). + /// Note: Common lon/lat CRS representations (EPSG:4326, OGC:CRS84) are canonicalized + /// to `None` during serialization to match Parquet conventions. + #[serde(skip_serializing_if = "Option::is_none")] + pub crs: Option<serde_json::Value>, + /// The edge interpolation algorithm of the [`WkbType`], if present. + #[serde(skip_serializing_if = "Option::is_none")] + pub algorithm: Option<String>, +} + +impl Metadata { + /// Constructs a new [`Metadata`] with the given CRS and algorithm. + /// + /// If a CRS is provided, and can be parsed as JSON, it will be stored as a JSON object instead + /// of its string representation. + pub fn new(crs: Option<&str>, algorithm: Option<String>) -> Self { + let crs = crs.map(|c| match serde_json::from_str(c) { + Ok(crs) => crs, + Err(_) => serde_json::Value::String(c.to_string()), + }); + + Self { crs, algorithm } + } + + /// Returns a [`Hint`] to the likely underlying Logical Type that this [`Metadata`] represents. + pub fn type_hint(&self) -> Hint { + match &self.algorithm { + Some(s) if s.to_lowercase() == "planar" => Hint::Geometry, + Some(_) => Hint::Geography, + None => Hint::Geometry, + } + } +} + +/// Well-Known Binary (WKB) [`ExtensionType`] for geospatial data. +/// +/// Represents the canonical Arrow Extension Type for storing +/// [GeoArrow](https://github.com/geoarrow/geoarrow) data. +#[derive(Debug, Default)] +pub struct WkbType(Metadata); + +impl WkbType { + /// Constructs a new [`WkbType`] with the given [`Metadata`]. + /// + /// If `None` is provided, default (empty) metadata is used. + pub fn new(metadata: Option<Metadata>) -> Self { + Self(metadata.unwrap_or_default()) + } +} + +type ArrowResult<T> = Result<T, ArrowError>; +impl ExtensionType for WkbType { + const NAME: &'static str = "geoarrow.wkb"; + + type Metadata = Metadata; + + fn metadata(&self) -> &Self::Metadata { + &self.0 + } + + fn serialize_metadata(&self) -> Option<String> { + use serde_json::Value; + + // Detect common representations of lon/lat and convert them to the canonical Parquet + // representation for lon/lat (empty/omitted) + let crs = &self.0.crs.as_ref().and_then(|crs| match crs { + Value::String(s) if s == "EPSG:4326" || s == "OGC:CRS84" => None, + Value::Object(_) => match (&crs["id"]["authority"], &crs["id"]["code"]) { + (Value::String(auth), Value::String(code)) if auth == "OGC" && code == "CRS84" => { + None + } + (Value::String(auth), Value::String(code)) if auth == "EPSG" && code == "4326" => { + None + } + (Value::String(auth), Value::Number(code)) + if auth == "EPSG" && code.as_i64() == Some(4326) => + { + None + } + _ => Some(crs), + }, + _ => Some(crs), + }); + + let md = Metadata { + crs: (*crs).cloned(), + algorithm: self.0.algorithm.clone(), + }; + + serde_json::to_string(&md).ok() Review Comment: I was able to make this all much cleaner and more readable thanks to this suggestion. 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