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static const char SCCSID[]="@(#)PJ_vandg4.c 4.1 94/02/15 GIE REL";
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PROJ_HEAD(vandg4, "van der Grinten IV") "\n\tMisc Sph, no inv.";
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#define TWORPI 0.63661977236758134308
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FORWARD(s_forward); /* spheroid */
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double x1, t, bt, ct, ft, bt2, ct2, dt, dt2;
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if (fabs(lp.phi) < TOL) {
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} else if (fabs(lp.lam) < TOL || fabs(fabs(lp.phi) - HALFPI) < TOL) {
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bt = fabs(TWORPI * lp.phi);
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ct = 0.5 * (bt * (8. - bt * (2. + bt2)) - 5.)
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dt = sqrt(dt * dt - 4.);
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if ((fabs(lp.lam) - HALFPI) < 0.) dt = -dt;
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x1 = bt + ct; x1 *= x1;
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ft = x1 * (bt2 + ct2 * dt2 - 1.) + (1.-bt2) * (
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bt2 * (t * t + 4. * ct2) +
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ct2 * (12. * bt * ct + 4. * ct2) );
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x1 = (dt*(x1 + ct2 - 1.) + 2.*sqrt(ft)) /
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xy.y = HALFPI * sqrt(1. + dt * fabs(x1) - x1 * x1);
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if (lp.lam < 0.) xy.x = -xy.x;
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if (lp.phi < 0.) xy.y = -xy.y;
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FREEUP; if (P) pj_dalloc(P); }
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ENTRY0(vandg4) P->es = 0.; P->fwd = s_forward; ENDENTRY(P)