✨ CogReader ndarray method to decode TIFF into an ndarray Array (#10)

* ♻️ Turn image decoding into a Vec code into a method call

Making the decoder.read_image() code an impl method under the CogReader struct. Reworded the previous panic message into an unimplemented error with a more helpful message that dtypes other than float32 are not yet supported.

* ✨ Implement ndarray method in CogReader struct

Move the previous tiff-decoder -> Vec -> ndarray code to an impl method under CogReader. Was going to separate the as_vec and ndarray code, but got caught up with move semantics when trying to use the methods in pyo3, so just having an all-in-one ndarray method now. Added a unit test to check that an ndarray is properly returned.

src/io/geotiff.rs

@@ -21,6 +21,25 @@ impl<R: Read + Seek> CogReader<R> {
         Ok(Self { decoder })
     }
 
+    /// Decode GeoTIFF image to an [`ndarray::Array`]
+    fn ndarray(&mut self) -> TiffResult<Array2<f32>> {
+        // Get image dimensions
+        let (width, height): (u32, u32) = self.decoder.dimensions()?;
+
+        // Get image pixel data
+        let decode_result = self.decoder.read_image()?;
+        let image_data: Vec<f32> = match decode_result {
+            DecodingResult::F32(img_data) => img_data,
+            _ => unimplemented!("Data types other than float32 are not yet supported."),
+        };
+
+        // Put image pixel data into an ndarray
+        let vec_data = Array2::from_shape_vec((height as usize, width as usize), image_data)
+            .map_err(|_| TiffFormatError::InvalidDimensions(height, width))?;
+
+        Ok(vec_data)
+    }
+
     /// Affine transformation for 2D matrix extracted from TIFF tag metadata, used to transform
     /// image pixel (row, col) coordinates to and from geographic/projected (x, y) coordinates.
     ///
@@ -76,17 +95,8 @@ pub fn read_geotiff<R: Read + Seek>(stream: R) -> TiffResult<Array2<f32>> {
     // Open TIFF stream with decoder
     let mut reader = CogReader::new(stream)?;
 
-    // Get image dimensions
-    let (width, height): (u32, u32) = reader.decoder.dimensions()?;
-
-    // Get image pixel data
-    let DecodingResult::F32(img_data) = reader.decoder.read_image()? else {
-        panic!("Cannot read band data")
-    };
-
-    // Put image pixel data into an ndarray
-    let vec_data = Array2::from_shape_vec((height as usize, width as usize), img_data)
-        .map_err(|_| TiffFormatError::InvalidDimensions(height, width))?;
+    // Decode TIFF into ndarray
+    let vec_data: Array2<f32> = reader.ndarray()?;
 
     Ok(vec_data)
 }
@@ -96,6 +106,7 @@ mod tests {
     use std::io::{Cursor, Seek, SeekFrom};
 
     use geo::AffineTransform;
+    use ndarray::array;
     use object_store::parse_url;
     use tempfile::tempfile;
     use tiff::encoder::{colortype, TiffEncoder};
@@ -131,6 +142,23 @@ mod tests {
         assert_eq!(arr.mean(), Some(14.0));
     }
 
+    #[tokio::test]
+    async fn test_cogreader_ndarray() {
+        let cog_url: &str = "https://github.com/rasterio/rasterio/raw/1.3.9/tests/data/float32.tif";
+        let tif_url = Url::parse(cog_url).unwrap();
+        let (store, location) = parse_url(&tif_url).unwrap();
+
+        let result = store.get(&location).await.unwrap();
+        let bytes = result.bytes().await.unwrap();
+        let stream = Cursor::new(bytes);
+
+        let mut reader = CogReader::new(stream).unwrap();
+        let array = reader.ndarray().unwrap();
+
+        assert_eq!(array.shape(), [2, 3]);
+        assert_eq!(array, array![[1.41, 1.23, 0.78], [0.32, -0.23, -1.88]])
+    }
+
     #[tokio::test]
     async fn test_cogreader_transform() {
         let cog_url: &str =