BlakeOrth commented on code in PR #8801:
URL: https://github.com/apache/arrow-rs/pull/8801#discussion_r2504856079
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parquet-geospatial/src/crs.rs:
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@@ -0,0 +1,97 @@
+use std::{collections::HashMap, sync::Arc};
+
+use arrow_schema::{Schema, SchemaBuilder};
+use serde_json::{Value, json};
+
+#[derive(Debug)]
+pub enum Crs {
+ Projjson(serde_json::Value),
+ Srid(u64),
+ Other(String),
+}
+
+impl Crs {
+ // TODO: make fallible
+ fn try_from_parquet_str(crs: &str, metadata: &HashMap<String, String>) ->
Self {
+ let de: Value = serde_json::from_str(crs).unwrap();
+
+ // A CRS that does not exist or is empty defaults to 4326
+ // TODO: http link to parquet geospatial doc
+ let Some(crs) = de["crs"].as_str() else {
+ return Crs::Srid(4326);
+ };
+
+ if let Some(key) = crs.strip_prefix("projjson:") {
+ let Some(proj_meta) = metadata.get(key) else {
+ panic!("Failed to find key in meta: {:?}", metadata)
+ };
+
+ Self::Projjson(serde_json::from_str(proj_meta).unwrap())
+ } else if let Some(srid) = crs.strip_prefix("srid:") {
+ Self::Srid(srid.parse().unwrap())
+ } else {
Review Comment:
Just to make sure I'm understanding this case correctly. The incoming
metadata would look like:
`{"crs": "<PROJJSON string>"}` (omitting the `projjson:` prefix)
It does seem convenient to try to parse the above case as json, and try to
detect if it seems like a PROJJSON object. Since we don't have access to an
actual PROJ parser here I would be a little bit concerned about the potential
for false positives or potentially malformed PROJ objects. I don't think I feel
super strongly about those concerns though. It seems like it's one of those
trade offs between user convenience vs guaranteed correctness.
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