From 85568fa7a4b511975c88074a77add2d2e7794ce3 Mon Sep 17 00:00:00 2001
From: David Marteau <dmarteau@3liz.com>
Date: Tue, 15 Oct 2024 00:59:07 +0200
Subject: [PATCH] Add Equidistant Cylindrical 'eqc' projection

---
 proj4rs/src/projections/eqc.rs | 89 ++++++++++++++++++++++++++++++++++
 proj4rs/src/projections/mod.rs |  4 +-
 projections.md                 |  3 +-
 3 files changed, 94 insertions(+), 2 deletions(-)
 create mode 100644 proj4rs/src/projections/eqc.rs

diff --git a/proj4rs/src/projections/eqc.rs b/proj4rs/src/projections/eqc.rs
new file mode 100644
index 0000000..4b66530
--- /dev/null
+++ b/proj4rs/src/projections/eqc.rs
@@ -0,0 +1,89 @@
+//!
+//! From proj/eqc.cpp
+//!
+//! See also <https://proj.org/operations/projections/eqc.html>
+//!
+//! Simplest of all projections
+//!
+//! eqc: "Equidistant Cylindrical (Plate Carree)"
+//!
+
+use crate::ellps::Ellipsoid;
+use crate::errors::{Error, Result};
+use crate::parameters::ParamList;
+use crate::proj::ProjData;
+
+// Projection stub
+super::projection! { eqc }
+
+#[derive(Debug, Clone)]
+pub(crate) struct Projection {
+    rc: f64,
+    phi0: f64,
+}
+
+impl Projection {
+    pub fn eqc(p: &mut ProjData, params: &ParamList) -> Result<Self> {
+        let rc = params.try_angular_value("lat_ts")?.unwrap_or(0.).cos();
+        if rc <= 0. {
+            return Err(Error::InvalidParameterValue("lat_ts should be <= 90°"));
+        }
+        p.ellps = Ellipsoid::sphere(p.ellps.a)?;
+        Ok(Self { rc, phi0: p.phi0 })
+    }
+
+    #[inline(always)]
+    pub fn forward(&self, lam: f64, phi: f64, z: f64) -> Result<(f64, f64, f64)> {
+        Ok((lam * self.rc, phi - self.phi0, z))
+    }
+
+    #[inline(always)]
+    pub fn inverse(&self, x: f64, y: f64, z: f64) -> Result<(f64, f64, f64)> {
+        Ok((x / self.rc, y + self.phi0, z))
+    }
+
+    pub const fn has_inverse() -> bool {
+        true
+    }
+
+    pub const fn has_forward() -> bool {
+        true
+    }
+}
+
+
+#[cfg(test)]
+mod tests {
+    use crate::math::consts::EPS_10;
+    use crate::proj::Proj;
+    use crate::tests::utils::{test_proj_forward, test_proj_inverse};
+
+    #[test]
+    fn proj_eqc_wgs84() {
+        let p = Proj::from_proj_string("+proj=eqc +ellps=WGS84").unwrap();
+
+        println!("{:#?}", p.projection());
+
+        let inputs = [
+            ((2., 47., 0.), (222638.98158654713, 5232016.06728385761, 0.)),
+        ];
+
+        test_proj_forward(&p, &inputs, EPS_10);
+        test_proj_inverse(&p, &inputs, EPS_10);
+    }
+
+    #[test]
+    fn proj_eqc_lat_ts() {
+        let p = Proj::from_proj_string("+proj=eqc +lat_ts=30 +lon_0=-90").unwrap();
+
+        println!("{:#?}", p.projection());
+
+        let inputs = [
+            ((-88., 30., 0.), (192811.01392664597, 3339584.72379820701, 0.)),
+        ];
+
+        test_proj_forward(&p, &inputs, EPS_10);
+        test_proj_inverse(&p, &inputs, EPS_10);
+    }
+
+}
diff --git a/proj4rs/src/projections/mod.rs b/proj4rs/src/projections/mod.rs
index 00cd8fc..2f789a2 100644
--- a/proj4rs/src/projections/mod.rs
+++ b/proj4rs/src/projections/mod.rs
@@ -134,7 +134,7 @@ macro_rules! projection {
 use downcast;
 use projection;
 
-const NUM_PROJECTIONS: usize = 21;
+const NUM_PROJECTIONS: usize = 22;
 
 macro_rules! declare_projections {
     ($(($name:ident $(,)? $($init:ident),*)),+ $(,)?) => {
@@ -161,6 +161,7 @@ macro_rules! declare_projections {
 // ---------------------------
 
 pub mod aea;
+pub mod eqc;
 pub mod estmerc;
 pub mod etmerc;
 pub mod geocent;
@@ -190,6 +191,7 @@ declare_projections! [
     (laea),
     (moll, wag4, wag5),
     (geos),
+    (eqc),
 ];
 
 ///
diff --git a/projections.md b/projections.md
index 4e4331a..c1266ca 100644
--- a/projections.md
+++ b/projections.md
@@ -15,6 +15,7 @@
     (laea),
     (moll, wag4, wag5),
     (geos),
+    (eqc),
 ]
 ```
 
@@ -25,7 +26,7 @@
 - [-] bonne
 - [-] cass
 - [-] cea
-- [-] eqc
+- [+] eqc
 - [-] eqdc
 - [-] eqearth
 - [-] equi