aboutsummaryrefslogtreecommitdiff
path: root/src/projections/igh_o.cpp
diff options
context:
space:
mode:
Diffstat (limited to 'src/projections/igh_o.cpp')
-rw-r--r--src/projections/igh_o.cpp268
1 files changed, 268 insertions, 0 deletions
diff --git a/src/projections/igh_o.cpp b/src/projections/igh_o.cpp
new file mode 100644
index 00000000..785a8784
--- /dev/null
+++ b/src/projections/igh_o.cpp
@@ -0,0 +1,268 @@
+#define PJ_LIB__
+
+#include <errno.h>
+#include <math.h>
+
+#include "proj.h"
+#include "proj_internal.h"
+
+PROJ_HEAD(igh_o, "Interrupted Goode Homolosine Oceanic View") "\n\tPCyl, Sph";
+
+/*
+This projection is a variant of the Interrupted Goode Homolosine
+projection that emphasizes ocean areas. The projection is a
+compilation of 12 separate sub-projections. Sinusoidal projections
+are found near the equator and Mollweide projections are found at
+higher latitudes. The transition between the two occurs at 40 degrees
+latitude and is represented by `phi_boundary`.
+
+Each sub-projection is assigned an integer label
+numbered 1 through 12. Most of this code contains logic to assign
+the labels based on latitude (phi) and longitude (lam) regions.
+
+Original Reference:
+J. Paul Goode (1925) THE HOMOLOSINE PROJECTION: A NEW DEVICE FOR
+ PORTRAYING THE EARTH'S SURFACE ENTIRE, Annals of the Association of
+ American Geographers, 15:3, 119-125, DOI: 10.1080/00045602509356949
+*/
+
+C_NAMESPACE PJ *pj_sinu(PJ *), *pj_moll(PJ *);
+
+/*
+Transition from sinusoidal to Mollweide projection
+Latitude (phi): 40deg 44' 11.8"
+*/
+
+static const double phi_boundary = (40 + 44/60. + 11.8/3600.) * DEG_TO_RAD;
+
+static const double d10 = 10 * DEG_TO_RAD;
+static const double d20 = 20 * DEG_TO_RAD;
+static const double d50 = 50 * DEG_TO_RAD;
+static const double d60 = 60 * DEG_TO_RAD;
+static const double d90 = 90 * DEG_TO_RAD;
+static const double d110 = 110 * DEG_TO_RAD;
+static const double d140 = 140 * DEG_TO_RAD;
+static const double d150 = 150 * DEG_TO_RAD;
+static const double d160 = 160 * DEG_TO_RAD;
+static const double d130 = 130 * DEG_TO_RAD;
+static const double d180 = 180 * DEG_TO_RAD;
+
+static const double EPSLN = 1.e-10; /* allow a little 'slack' on zone edge positions */
+
+namespace { // anonymous namespace
+struct pj_opaque {
+ struct PJconsts* pj[12]; \
+ double dy0;
+};
+} // anonymous namespace
+
+
+/*
+Assign an integer index representing each of the 12
+sub-projection zones based on latitude (phi) and
+longitude (lam) ranges.
+*/
+
+static PJ_XY igh_o_s_forward (PJ_LP lp, PJ *P) { /* Spheroidal, forward */
+ PJ_XY xy;
+ struct pj_opaque *Q = static_cast<struct pj_opaque*>(P->opaque);
+ int z;
+
+ if (lp.phi >= phi_boundary) {
+ if (lp.lam <= -d90) z = 1;
+ else if (lp.lam >= d60) z = 3;
+ else z = 2;
+ }
+ else if (lp.phi >= 0) {
+ if (lp.lam <= -d90) z = 4;
+ else if (lp.lam >= d60) z = 6;
+ else z = 5;
+ }
+ else if (lp.phi >= -phi_boundary) {
+ if (lp.lam <= -d60) z = 7;
+ else if (lp.lam >= d90) z = 9;
+ else z = 8;
+ }
+ else {
+ if (lp.lam <= -d60) z = 10;
+ else if (lp.lam >= d90) z = 12;
+ else z = 11;
+ }
+
+ lp.lam -= Q->pj[z-1]->lam0;
+ xy = Q->pj[z-1]->fwd(lp, Q->pj[z-1]);
+ xy.x += Q->pj[z-1]->x0;
+ xy.y += Q->pj[z-1]->y0;
+
+ return xy;
+}
+
+
+static PJ_LP igh_o_s_inverse (PJ_XY xy, PJ *P) { /* Spheroidal, inverse */
+ PJ_LP lp = {0.0,0.0};
+ struct pj_opaque *Q = static_cast<struct pj_opaque*>(P->opaque);
+ const double y90 = Q->dy0 + sqrt(2.0); /* lt=90 corresponds to y=y0+sqrt(2) */
+
+ int z = 0;
+ if (xy.y > y90+EPSLN || xy.y < -y90+EPSLN) /* 0 */
+ z = 0;
+ else if (xy.y >= phi_boundary)
+ if (xy.x <= -d90) z = 1;
+ else if (xy.x >= d60) z = 3;
+ else z = 2;
+ else if (xy.y >= 0)
+ if (xy.x <= -d90) z = 4;
+ else if (xy.x >= d60) z = 6;
+ else z = 5;
+ else if (xy.y >= -phi_boundary) {
+ if (xy.x <= -d60) z = 7;
+ else if (xy.x >= d90) z = 9;
+ else z = 8;
+ }
+ else {
+ if (xy.x <= -d60) z = 10;
+ else if (xy.x >= d90) z = 12;
+ else z = 11;
+ }
+
+ if (z) {
+ bool ok = false;
+
+ xy.x -= Q->pj[z-1]->x0;
+ xy.y -= Q->pj[z-1]->y0;
+ lp = Q->pj[z-1]->inv(xy, Q->pj[z-1]);
+ lp.lam += Q->pj[z-1]->lam0;
+
+ switch (z) {
+ /* Plot projectable ranges with exetension lobes in zones 1 & 3 */
+ case 1: ok = (lp.lam >= -d180-EPSLN && lp.lam <= -d90+EPSLN) ||
+ ((lp.lam >= d160-EPSLN && lp.lam <= d180+EPSLN) &&
+ (lp.phi >= d50-EPSLN && lp.phi <= d90+EPSLN)); break;
+ case 2: ok = (lp.lam >= -d90-EPSLN && lp.lam <= d60+EPSLN); break;
+ case 3: ok = (lp.lam >= d60-EPSLN && lp.lam <= d180+EPSLN) ||
+ ((lp.lam >= -d180-EPSLN && lp.lam <= -d160+EPSLN) &&
+ (lp.phi >= d50-EPSLN && lp.phi <= d90+EPSLN)); break;
+ case 4: ok = (lp.lam >= -d180-EPSLN && lp.lam <= -d90+EPSLN); break;
+ case 5: ok = (lp.lam >= -d90-EPSLN && lp.lam <= d60+EPSLN); break;
+ case 6: ok = (lp.lam >= d60-EPSLN && lp.lam <= d180+EPSLN); break;
+ case 7: ok = (lp.lam >= -d180-EPSLN && lp.lam <= -d60+EPSLN); break;
+ case 8: ok = (lp.lam >= -d60-EPSLN && lp.lam <= d90+EPSLN); break;
+ case 9: ok = (lp.lam >= d90-EPSLN && lp.lam <= d180+EPSLN); break;
+ case 10: ok = (lp.lam >= -d180-EPSLN && lp.lam <= -d60+EPSLN); break;
+ case 11: ok = (lp.lam >= -d60-EPSLN && lp.lam <= d90+EPSLN); break;
+ case 12: ok = (lp.lam >= d90-EPSLN && lp.lam <= d180+EPSLN); break;
+
+ }
+ z = (!ok? 0: z); /* projectable? */
+ }
+
+ if (!z) lp.lam = HUGE_VAL;
+ if (!z) lp.phi = HUGE_VAL;
+
+ return lp;
+}
+
+
+static PJ *destructor (PJ *P, int errlev) {
+ int i;
+ if (nullptr==P)
+ return nullptr;
+
+ if (nullptr==P->opaque)
+ return pj_default_destructor (P, errlev);
+
+ struct pj_opaque *Q = static_cast<struct pj_opaque*>(P->opaque);
+
+ for (i = 0; i < 12; ++i) {
+ if (Q->pj[i])
+ Q->pj[i]->destructor(Q->pj[i], errlev);
+ }
+
+ return pj_default_destructor(P, errlev);
+}
+
+
+
+/*
+ Zones:
+
+ -180 -90 60 180
+ +---------+----------------+-------------+ Zones 1,2,3,10,11 & 12:
+ |1 |2 |3 | Mollweide projection
+ | | | |
+ +---------+----------------+-------------+ Zones 4,5,6,7,8 & 9:
+ |4 |5 |6 | Sinusoidal projection
+ | | | |
+ 0 +---------+--+-------------+--+----------+
+ |7 |8 |9 |
+ | | | |
+ +------------+----------------+----------+
+ |10 |11 |12 |
+ | | | |
+ +------------+----------------+----------+
+ -180 -60 90 180
+*/
+
+static bool setup_zone(PJ *P, struct pj_opaque *Q, int n,
+ PJ*(*proj_ptr)(PJ*), double x_0,
+ double y_0, double lon_0) {
+ if (!(Q->pj[n-1] = proj_ptr(nullptr))) return false;
+ if (!(Q->pj[n-1] = proj_ptr(Q->pj[n-1]))) return false;
+ Q->pj[n-1]->ctx = P->ctx;
+ Q->pj[n-1]->x0 = x_0;
+ Q->pj[n-1]->y0 = y_0;
+ Q->pj[n-1]->lam0 = lon_0;
+ return true;
+}
+
+PJ *PROJECTION(igh_o) {
+ PJ_XY xy1, xy4;
+ PJ_LP lp = { 0, phi_boundary };
+ struct pj_opaque *Q = static_cast<struct pj_opaque*>(pj_calloc (1, sizeof (struct pj_opaque)));
+ if (nullptr==Q)
+ return pj_default_destructor (P, ENOMEM);
+ P->opaque = Q;
+
+
+ /* sinusoidal zones */
+ if (!setup_zone(P, Q, 4, pj_sinu, -d140, 0, -d140) ||
+ !setup_zone(P, Q, 5, pj_sinu, d10, 0, d10) ||
+ !setup_zone(P, Q, 6, pj_sinu, d130, 0, d130) ||
+ !setup_zone(P, Q, 7, pj_sinu, -d110, 0, -d110) ||
+ !setup_zone(P, Q, 8, pj_sinu, d20, 0, d20) ||
+ !setup_zone(P, Q, 9, pj_sinu, d150, 0, d150))
+ {
+ return destructor(P, ENOMEM);
+ }
+
+
+ /* mollweide zones */
+ if (!setup_zone(P, Q, 1, pj_moll, -d140, 0, -d140)) {
+ return destructor(P, ENOMEM);
+ }
+
+ /* y0 ? */
+ xy1 = Q->pj[0]->fwd(lp, Q->pj[0]); /* zone 1 */
+ xy4 = Q->pj[3]->fwd(lp, Q->pj[3]); /* zone 4 */
+ /* y0 + xy1.y = xy4.y for lt = 40d44'11.8" */
+ Q->dy0 = xy4.y - xy1.y;
+
+ Q->pj[0]->y0 = Q->dy0;
+
+ /* mollweide zones (cont'd) */
+ if (!setup_zone(P, Q, 2, pj_moll, d10, Q->dy0, d10) ||
+ !setup_zone(P, Q, 3, pj_moll, d130, Q->dy0, d130) ||
+ !setup_zone(P, Q, 10, pj_moll, -d110, -Q->dy0, -d110) ||
+ !setup_zone(P, Q, 11, pj_moll, d20, -Q->dy0, d20) ||
+ !setup_zone(P, Q, 12, pj_moll, d150, -Q->dy0, d150))
+ {
+ return destructor(P, ENOMEM);
+ }
+
+ P->inv = igh_o_s_inverse;
+ P->fwd = igh_o_s_forward;
+ P->destructor = destructor;
+ P->es = 0.;
+
+ return P;
+}
generated by cgit v1.2.3 (git 2.25.1) at 2026-01-06 04:45:30 +0000