From 6f08755534fd26519d5a7099069f4a55551ade8c Mon Sep 17 00:00:00 2001
From: Felix Palmer <felixpalmer@gmail.com>
Date: Fri, 17 Apr 2026 11:32:59 +0200
Subject: [PATCH] Feature: IVEA projection

---
 src/pj_list.h                  |  1 +
 src/projections/polyhedral.cpp | 15 +++++++++++++++
 test/render_nets.sh            |  4 ++++
 test/unit/test_polyhedral.cpp  |  1 +
 4 files changed, 21 insertions(+)

diff --git a/src/pj_list.h b/src/pj_list.h
index 4828e53a3a..888a51e155 100644
--- a/src/pj_list.h
+++ b/src/pj_list.h
@@ -80,6 +80,7 @@ PROJ_HEAD(imw_p, "International Map of the World Polyconic")
 PROJ_HEAD(dsea, "Dodecahedral Snyder Equal Area")
 PROJ_HEAD(isea, "Icosahedral Snyder Equal Area")
 PROJ_HEAD(isea2, "Icosahedral Snyder Equal Area (generalized)")
+PROJ_HEAD(ivea, "Icosahedral Vertex Equal Area")
 PROJ_HEAD(kav5, "Kavrayskiy V")
 PROJ_HEAD(kav7, "Kavrayskiy VII")
 PROJ_HEAD(krovak, "Krovak")
diff --git a/src/projections/polyhedral.cpp b/src/projections/polyhedral.cpp
index 9d2204a6fa..bab508cb6f 100644
--- a/src/projections/polyhedral.cpp
+++ b/src/projections/polyhedral.cpp
@@ -131,6 +131,21 @@ PJ *PJ_PROJECTION(isea2) { // TODO rename to `isea`?
     return P;
 }
 
+PROJ_HEAD(ivea, "Icosahedral Vertex Equal Area") "\n\tSph";
+constexpr double IVEA_AZ_DEG = 36.0;
+PJ *PJ_PROJECTION(ivea) {
+    auto *Q = static_cast<pj_polyhedral_data *>(calloc(1, sizeof(pj_polyhedral_data)));
+    if (nullptr == Q) return pj_default_destructor(P, PROJ_ERR_OTHER /*ENOMEM*/);
+    P->opaque = Q;
+
+    polyhedral::load_triangles(Q, decakis_dodecahedron::SPH_TRI, nets::dsea::icosahedron::FACE_TRI);
+    polyhedral::set_orient_from_angles(Q, ISEA_STD_LAT_DEG, ISEA_STD_LON_DEG, IVEA_AZ_DEG);
+
+    P->fwd = polyhedral_fwd;
+    P->inv = polyhedral_inv;
+    return P;
+}
+
 PROJ_HEAD(tsea, "Tetrahedral Snyder Equal Area") "\n\tSph";
 PJ *PJ_PROJECTION(tsea) {
     auto *Q = static_cast<pj_polyhedral_data *>(calloc(1, sizeof(pj_polyhedral_data)));
diff --git a/test/render_nets.sh b/test/render_nets.sh
index 18fcc85213..881d585cf0 100755
--- a/test/render_nets.sh
+++ b/test/render_nets.sh
@@ -31,6 +31,10 @@ $RENDER --proj="+proj=isea2 +R=1" \
     --title="ISEA: Icosahedral Snyder Equal Area" \
     -o isea_net.png
 
+$RENDER --proj="+proj=ivea +R=1" \
+    --title="IVEA: DSEA unfolded onto icosahedral net" \
+    -o ivea_net.png
+
 $RENDER --proj="+proj=tsea +R=1" \
     --title="TSEA: Tetrahedral Snyder Equal Area" \
     -o tsea_net.png
diff --git a/test/unit/test_polyhedral.cpp b/test/unit/test_polyhedral.cpp
index 3b15aeff67..38456197d1 100644
--- a/test/unit/test_polyhedral.cpp
+++ b/test/unit/test_polyhedral.cpp
@@ -43,6 +43,7 @@ static const char *proj_strings[] = {
     "+proj=dsea +net=two_flower +R=1",
     "+proj=dsea +net=icosahedron +R=1",
     "+proj=isea2 +R=1",
+    "+proj=ivea +R=1",
 };
 
 static void roundtrip_test(const char *proj_string, double tolerance) {