Copilot commented on code in PR #2677:
URL: https://github.com/apache/sedona/pull/2677#discussion_r2870963996
##########
common/src/main/java/org/apache/sedona/common/raster/RasterAccessors.java:
##########
@@ -359,4 +363,94 @@ public static RasterMetadata rasterMetadata(GridCoverage2D
raster) throws Factor
(int) meta[10],
(int) meta[11]);
}
+
+ /**
+ * Returns the CRS of a raster as PROJJSON string.
+ *
+ * @param raster The input raster.
+ * @return The CRS definition as PROJJSON string, or null if no CRS is set.
+ */
+ public static String crs(GridCoverage2D raster) {
+ return crs(raster, "projjson");
+ }
+
+ /**
+ * Returns the CRS of a raster in the specified format.
+ *
+ * @param raster The input raster.
+ * @param format The desired output format: "projjson", "wkt2", "wkt1", or
"proj".
+ * @return The CRS definition string in the requested format, or null if no
CRS is set.
+ */
+ public static String crs(GridCoverage2D raster, String format) {
+ if (format == null || format.trim().isEmpty()) {
+ format = "projjson";
+ }
+ CoordinateReferenceSystem crsDef = raster.getCoordinateReferenceSystem();
+ if (crsDef instanceof DefaultEngineeringCRS) {
+ if (((DefaultEngineeringCRS) crsDef).isWildcard()) {
+ return null;
+ }
+ }
+
+ // Get WKT1 representation from GeoTools (native, no conversion needed)
+ String wkt1;
+ if (crsDef instanceof Formattable) {
+ wkt1 = ((Formattable) crsDef).toWKT(2, false);
+ } else {
+ wkt1 = crsDef.toWKT();
+ }
+
+ String fmt = format.toLowerCase(Locale.ROOT).trim();
+ if ("wkt1".equals(fmt) || "wkt".equals(fmt)) {
+ return wkt1;
+ }
+
+ // For all other formats, convert through proj4sedona.
+ // Prefer EPSG SRID when available: GeoTools WKT1 projection names (e.g.
Mercator_2SP)
+ // may not be recognized by proj4sedona, but EPSG codes always work.
+ try {
+ Proj proj;
+ int srid = srid(raster);
+ if (srid > 0) {
+ try {
+ proj = new Proj("EPSG:" + srid);
+ } catch (Exception e) {
+ // EPSG code not recognized by proj4sedona, fall back to WKT1
+ proj = new Proj(wkt1);
Review Comment:
In the `srid > 0` branch, if `new Proj("EPSG:" + srid)` fails, the fallback
uses `new Proj(wkt1)` without attempting the same projection-name normalization
that the `srid == 0` branch does. This can cause CRS export to fail
unnecessarily when proj4sedona doesn’t recognize the EPSG code and also can’t
parse GeoTools’ WKT1 projection name (e.g., Mercator_2SP). Consider applying
`normalizeWkt1ForProj4sedona(wkt1)` (and retry) in this fallback path as well.
```suggestion
// EPSG code not recognized by proj4sedona, fall back to WKT1.
// proj4sedona may not recognize some GeoTools projection names
(e.g. Mercator_2SP),
// so normalize the projection name and retry if needed.
try {
proj = new Proj(wkt1);
} catch (Exception wktError) {
String normalized =
CrsNormalization.normalizeWkt1ForProj4sedona(wkt1);
if (!normalized.equals(wkt1)) {
proj = new Proj(normalized);
} else {
throw wktError;
}
}
```
##########
docs/api/sql/Raster-Operators/RS_CRS.md:
##########
@@ -0,0 +1,101 @@
+<!--
+ 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.
+ -->
+
+# RS_CRS
+
+Introduction: Returns the coordinate reference system (CRS) of a raster as a
string in the specified format. If no format is specified, the CRS is returned
in PROJJSON format. Returns null if the raster has no CRS defined.
+
+Format:
+
+```
+RS_CRS (raster: Raster)
+```
+
+```
+RS_CRS (raster: Raster, format: String)
+```
+
+Since: `v1.9.0`
+
+## Supported output formats
+
+| Format | Description |
+| :--- | :--- |
+| `'projjson'` | PROJJSON format (default). Modern, machine-readable JSON
representation. |
+| `'wkt2'` | Well-Known Text 2 (ISO 19162). Modern standard CRS
representation. |
+| `'wkt1'` | Well-Known Text 1 (OGC 01-009). Legacy format, widely supported. |
+| `'proj'` | PROJ string format. Compact, human-readable representation. |
+
+## SQL Examples
+
+Getting CRS in default PROJJSON format:
+
+```sql
+SELECT RS_CRS(raster) FROM raster_table
+```
+
+Output:
+
+```json
+{
+ "$schema": "https://proj.org/schemas/v0.7/projjson.schema.json";,
+ "type": "GeographicCRS",
+ "name": "WGS 84",
+ ...
+}
+```
+
+Getting CRS in WKT1 format:
+
+```sql
+SELECT RS_CRS(raster, 'wkt1') FROM raster_table
+```
+
+Output:
+
+```
+GEOGCS["WGS 84",DATUM["WGS_1984",SPHEROID["WGS
84",6378137,298.257223563]],PRIMEM["Greenwich",0],UNIT["degree",0.0174532925199433]]
+```
+
+Getting CRS in PROJ string format:
+
+```sql
+SELECT RS_CRS(raster, 'proj') FROM raster_table
+```
+
+Output:
+
+```
++proj=longlat +datum=WGS84 +no_defs +type=crs
+```
+
+Getting CRS in WKT2 format:
+
+```sql
+SELECT RS_CRS(raster, 'wkt2') FROM raster_table
+```
+
+## Limitations
+
+The `wkt2`, `proj`, and `projjson` output formats are generated by
[proj4sedona](https://github.com/jiayuasu/proj4sedona) from the raster's
internal WKT1 CRS. This conversion may cause the following limitations:
+
+- **Unsupported projection types**: Some projection types (e.g., Krovak,
Hotine Oblique Mercator) cannot be exported to `wkt2`, `proj`, or `projjson`
formats and will throw an error. Use `'wkt1'` format for these.
+
+!!!note
+ Returns null if the raster has no CRS defined (e.g., when RS_SRID returns
0). The `wkt1` format always produces a lossless representation of the
internally stored CRS.
Review Comment:
The note implies `RS_SRID = 0` means “no CRS defined”, but this PR also
documents that `RS_SRID` returns 0 for custom (non-EPSG) CRS values set via
`RS_SetCRS`. That means `RS_CRS` can be non-null even when `RS_SRID` is 0.
Consider rewording this note to distinguish “no CRS defined” from “custom CRS
with no EPSG authority” (e.g., recommend `RS_CRS(...) IS NULL` to test for
missing CRS).
```suggestion
`RS_CRS` returns null only when the raster has no CRS defined. Note that
`RS_SRID` may return `0` either when no CRS is defined or when a custom
(non‑EPSG) CRS has been set via `RS_SetCRS`, so `RS_SRID = 0` does not always
mean “no CRS”. To test for a missing CRS, use `RS_CRS(raster) IS NULL`. The
`wkt1` format always produces a lossless representation of the internally
stored CRS.
```
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