add get_extent method

Author: sharkAndshark

martin/src/cog/errors.rs

@@ -51,4 +51,7 @@ pub enum CogError {
 
     #[error("Get full resolution failed from file: {0}")]
     GetFullResolutionFailed(PathBuf),
+
+    #[error("Get extent failed from file: {0}")]
+    GetExtentFailed(PathBuf),
 }

martin/src/cog/source.rs

@@ -376,6 +376,51 @@ fn get_meta(path: &PathBuf) -> Result<Meta, FileError> {
     })
 }
 
+fn get_extent(
+    transformation: Option<&[f64]>,
+    origin: Option<&[f64]>,
+    full_resolution: &[f64],
+    (full_width_pixel, full_height_pixel): (u32, u32),
+    path: &Path,
+) -> Result<[f64; 4], CogError> {
+    if let Some(matrix) = transformation {
+        let corners = [
+            [0, 0],
+            [0, full_height_pixel],
+            [full_width_pixel, 0],
+            [full_width_pixel, full_height_pixel],
+        ];
+        let transed = corners.map(|pixel| {
+            let i = f64::from(pixel[0]);
+            let j = f64::from(pixel[1]);
+            let x = matrix[3] + (matrix[0] * i) + (matrix[1] * j);
+            let y = matrix[7] + (matrix[4] * i) + (matrix[5] * j);
+            (x, y)
+        });
+        let mut min_x = transed[0].0;
+        let mut min_y = transed[1].1;
+        let mut max_x = transed[0].0;
+        let mut max_y = transed[1].1;
+        for (x, y) in transed {
+            if x <= min_x {
+                min_x = x;
+            }
+            if y <= min_y {
+                min_y = y;
+            }
+            if x >= max_x {
+                max_x = x;
+            }
+            if y >= max_y {
+                max_y = y;
+            }
+        }
+        return Ok([min_x, min_y, max_x, max_y]);
+    } else {
+        return Err(CogError::GetExtentFailed(path.to_path_buf()));
+    }
+}
+
 fn get_full_resolution(
     pixel_scale: Option<&[f64]>,
     transformation: Option<&[f64]>,