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Feature: IVEA projection #3

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Feature: IVEA projection #3

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1 change: 1 addition & 0 deletions src/pj_list.h
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Original file line number Diff line number Diff line change
Expand Up @@ -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")
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15 changes: 15 additions & 0 deletions src/projections/polyhedral.cpp
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Expand Up @@ -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);

@jerstlouis jerstlouis Jun 26, 2026 •
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@felixpalmer Curious about this (IVEA_AZ_DEG) here...

Is that the azimuth from DSEA's perspective?

If so, that might be problematic if trying to override +proj=ivea with +azi from ISEA/IVEA's perspective?

Is that positioning the vertices of the icosahedron at ISEA_STD_LAT_DEG, ISEA_STD_LON_DEG, or the vertices of the dodecahedron?

Also wondering if you updated this PR already or it still needs refactoring (it shows no conflict)?

@felixpalmer felixpalmer Jun 29, 2026

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No this PR is out of date, no point keeping it as the other branch has diverged too much

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)));
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4 changes: 4 additions & 0 deletions test/render_nets.sh
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Expand Up @@ -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
1 change: 1 addition & 0 deletions test/unit/test_polyhedral.cpp
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Expand Up @@ -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) {
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