Merge #274

274: Ability to get owned reference to inner geometry. r=rmanoka a=metasim

- [x] I agree to follow the project's [code of conduct](https://github.com/georust/gdal/blob/master/CODE_OF_CONDUCT.md).
- [x] I added an entry to `CHANGES.md` if knowledge of this change could be valuable to users.
---

Closes #269 



Co-authored-by: Simeon H.K. Fitch <fitch@astraea.io>

CHANGES.md

@@ -35,6 +35,10 @@
 
   - <https://github.com/georust/gdal/pull/246>
 
+- Add `GeometryRef<'a>` to reference owned nested geometry in a lifetime-safe way.
+
+  - <https://github.com/georust/gdal/pull/274>
+
 - Add support for MDArray API
 
   - <https://github.com/georust/gdal/pull/273>

src/vector/geometry.rs

@@ -1,6 +1,8 @@
 use std::cell::RefCell;
 use std::ffi::CString;
-use std::fmt::{self, Debug};
+use std::fmt::{self, Debug, Formatter};
+use std::marker::PhantomData;
+use std::ops::Deref;
 use std::ptr::null_mut;
 
 use libc::{c_char, c_double, c_int, c_void};
@@ -310,6 +312,15 @@ impl Geometry {
         Geometry::with_c_geometry(c_geom, false)
     }
 
+    /// Get a reference to the geometry at given `index`
+    pub fn get_geometry(&self, index: usize) -> GeometryRef {
+        let geom = unsafe { self.get_unowned_geometry(index) };
+        GeometryRef {
+            geom,
+            _lifetime: PhantomData::default(),
+        }
+    }
+
     pub fn add_geometry(&mut self, mut sub: Geometry) -> Result<()> {
         assert!(sub.owned);
         sub.owned = false;
@@ -444,6 +455,26 @@ pub fn geometry_type_to_name(ty: OGRwkbGeometryType::Type) -> String {
     _string(rv)
 }
 
+/// Reference to owned geometry
+pub struct GeometryRef<'a> {
+    geom: Geometry,
+    _lifetime: PhantomData<&'a ()>,
+}
+
+impl Deref for GeometryRef<'_> {
+    type Target = Geometry;
+
+    fn deref(&self) -> &Self::Target {
+        &self.geom
+    }
+}
+
+impl Debug for GeometryRef<'_> {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        Debug::fmt(&self.geom, f)
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use crate::spatial_ref::SpatialRef;

src/vector/vector_tests/mod.rs

@@ -122,6 +122,7 @@ where
 mod tests {
     use super::*;
     use crate::errors::{GdalError, Result};
+    use gdal_sys::OGRwkbGeometryType::{wkbLineString, wkbLinearRing, wkbPolygon};
 
     #[test]
     fn test_feature_count() {
@@ -508,6 +509,43 @@ mod tests {
         });
     }
 
+    #[test]
+    fn test_ring_points() {
+        let mut ring = Geometry::empty(wkbLinearRing).unwrap();
+        ring.add_point_2d((1179091.1646903288, 712782.8838459781));
+        ring.add_point_2d((1161053.0218226474, 667456.2684348812));
+        ring.add_point_2d((1214704.933941905, 641092.8288590391));
+        ring.add_point_2d((1228580.428455506, 682719.3123998424));
+        ring.add_point_2d((1218405.0658121984, 721108.1805541387));
+        ring.add_point_2d((1179091.1646903288, 712782.8838459781));
+        assert!(!ring.is_empty());
+        assert_eq!(ring.get_point_vec().len(), 6);
+        let mut poly = Geometry::empty(wkbPolygon).unwrap();
+        poly.add_geometry(ring.to_owned()).unwrap();
+        // Points are in ring, not containing geometry.
+        // NB: In Python SWIG bindings, `GetPoints` is fallible.
+        assert!(poly.get_point_vec().is_empty());
+        assert_eq!(poly.geometry_count(), 1);
+        let ring_out = poly.get_geometry(0);
+        // NB: `wkb()` shows it to be a `LINEARRING`, but returned type is LineString
+        assert_eq!(ring_out.geometry_type(), wkbLineString);
+        assert!(!&ring_out.is_empty());
+        assert_eq!(ring.get_point_vec(), ring_out.get_point_vec());
+    }
+
+    #[test]
+    fn test_get_inner_points() {
+        let geom = Geometry::bbox(0., 0., 1., 1.).unwrap();
+        assert!(!geom.is_empty());
+        assert_eq!(geom.geometry_count(), 1);
+        assert!(geom.area() > 0.);
+        assert_eq!(geom.geometry_type(), OGRwkbGeometryType::wkbPolygon);
+        assert!(geom.json().unwrap().contains("Polygon"));
+        let inner = geom.get_geometry(0);
+        let points = inner.get_point_vec();
+        assert!(!points.is_empty());
+    }
+
     #[test]
     fn test_wkt() {
         with_feature("roads.geojson", 236194095, |feature| {