feat: Implement GeoKeyDirectory

Cargo.toml

@@ -7,5 +7,6 @@ authors = ["Dominik Bucher <dobucher@ethz.ch>"]
 repository = "https://github.com/georust/geotiff"
 
 [dependencies]
+num_enum = "0.7"
 num-traits = "0.2"
 tiff = "0.9"

src/decoder_ext.rs

@@ -0,0 +1,37 @@
+use std::io::{Read, Seek};
+
+use tiff::decoder::Decoder;
+use tiff::tags::Tag;
+use tiff::TiffResult;
+
+use crate::geo_key_directory::GeoKeyDirectory;
+
+pub(super) trait DecoderExt {
+    fn geo_key_directory(&mut self) -> TiffResult<GeoKeyDirectory>;
+}
+
+impl<R: Read + Seek> DecoderExt for Decoder<R> {
+    fn geo_key_directory(&mut self) -> TiffResult<GeoKeyDirectory> {
+        let Some(directory_data) = self
+            .find_tag(Tag::GeoKeyDirectoryTag)?
+            .map(|v| v.into_u16_vec())
+            .transpose()?
+        else {
+            return Ok(GeoKeyDirectory::default());
+        };
+
+        let double_params_data = self
+            .find_tag(Tag::GeoDoubleParamsTag)?
+            .map(|v| v.into_f64_vec())
+            .transpose()?
+            .unwrap_or_else(|| Vec::with_capacity(0));
+
+        let ascii_params_data = self
+            .find_tag(Tag::GeoAsciiParamsTag)?
+            .map(|v| v.into_string())
+            .transpose()?
+            .unwrap_or_else(|| String::with_capacity(0));
+
+        GeoKeyDirectory::from_tag_data(directory_data, double_params_data, ascii_params_data)
+    }
+}