1 files changed, 69 insertions, 0 deletions
diff --git a/src/gpx.rs b/src/gpx.rs
new file mode 100644
index 0000000..7760ca5
--- /dev/null
+++ b/src/gpx.rs
@@ -0,0 +1,69 @@
+//! GPX data extraction functions.
+//!
+//! We *could* use the [gpx](https://github.com/georust/gpx) crate, but we don't care about much
+//! other than the coordinates of the tracks. By implementing the little functionality ourselves,
+//! we can use a fast XML parser ([roxmltree](https://github.com/RazrFalcon/roxmltree)).
+use std::{f64::consts::PI, fs, path::Path};
+
+use color_eyre::eyre::{eyre, Result};
+use roxmltree::{Document, Node, NodeType};
+
+#[derive(Debug, Copy, Clone, PartialEq)]
+pub struct Coordinates {
+    longitude: f64,
+    latitude: f64,
+}
+
+impl Coordinates {
+    /// Calculates the [Web Mercator
+    /// projection](https://en.wikipedia.org/wiki/Web_Mercator_projection) of the coordinates.
+    /// Returns the `(x, y)` coordinates.
+    pub fn web_mercator(self, zoom: u32) -> (u64, u64) {
+        let lambda = self.longitude.to_radians();
+        let phi = self.latitude.to_radians();
+        let x = 2u64.pow(zoom) as f64 / (2.0 * PI) * 256.0 * (lambda + PI);
+        let y = 2u64.pow(zoom) as f64 / (2.0 * PI) * 256.0 * (PI - (PI / 4.0 + phi / 2.0).tan().ln());
+        (x.floor() as u64, y.floor() as u64)
+    }
+}
+
+fn is_track_node(node: &Node) -> bool {
+    node.node_type() == NodeType::Element && node.tag_name().name() == "trk"
+}
+
+fn is_track_segment(node: &Node) -> bool {
+    node.node_type() == NodeType::Element && node.tag_name().name() == "trkseg"
+}
+
+fn is_track_point(node: &Node) -> bool {
+    node.node_type() == NodeType::Element && node.tag_name().name() == "trkpt"
+}
+
+pub fn extract_from_str(input: &str) -> Result<Vec<Coordinates>> {
+    let mut result = Vec::new();
+    let document = Document::parse(input)?;
+    for node in document.root_element().children().filter(is_track_node) {
+        for segment in node.children().filter(is_track_segment) {
+            for point in segment.children().filter(is_track_point) {
+                let latitude = point.attribute("lat")
+                    .and_then(|l| l.parse::<f64>().ok())
+                    .ok_or_else(|| eyre!("Invalid latitude"))?;
+                let longitude = point.attribute("lon")
+                    .and_then(|l| l.parse::<f64>().ok())
+                    .ok_or_else(|| eyre!("Invalid longitude"))?;
+                result.push(Coordinates { latitude, longitude });
+            }
+        }
+    }
+    Ok(result)
+}
+
+#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
+pub enum Compression {
+    None,
+}
+
+pub fn extract_from_file<P: AsRef<Path>>(path: P, _compression: Compression) -> Result<Vec<Coordinates>> {
+    let content = fs::read_to_string(path)?;
+    extract_from_str(&content)
+}