Function PROJECTION

ThirdParty/libproj/vtklibproj/src/projections/chamb.cpp:103–148

PJ *PROJECTION(chamb) {
    int i, j;
    char line[10];
    struct pj_opaque *Q = static_cast<struct pj_opaque*>(calloc (1, sizeof (struct pj_opaque)));
    if (nullptr==Q)
        return pj_default_destructor (P, PROJ_ERR_OTHER /*ENOMEM*/);
    P->opaque = Q;


    for (i = 0; i < 3; ++i) { /* get control point locations */
        (void)sprintf(line, "rlat_%d", i+1);
        Q->c[i].phi = pj_param(P->ctx, P->params, line).f;
        (void)sprintf(line, "rlon_%d", i+1);
        Q->c[i].lam = pj_param(P->ctx, P->params, line).f;
        Q->c[i].lam = adjlon(Q->c[i].lam - P->lam0);
        Q->c[i].cosphi = cos(Q->c[i].phi);
        Q->c[i].sinphi = sin(Q->c[i].phi);
    }
    for (i = 0; i < 3; ++i) { /* inter ctl pt. distances and azimuths */
        j = i == 2 ? 0 : i + 1;
        Q->c[i].v = vect(P->ctx,Q->c[j].phi - Q->c[i].phi, Q->c[i].cosphi, Q->c[i].sinphi,
            Q->c[j].cosphi, Q->c[j].sinphi, Q->c[j].lam - Q->c[i].lam);
        if (Q->c[i].v.r == 0.0)
        {
            proj_log_error(P, _("Invalid value for control points: they should be distinct"));
            return pj_default_destructor(P, PROJ_ERR_INVALID_OP_ILLEGAL_ARG_VALUE);
        }
        /* co-linearity problem ignored for now */
    }
    Q->beta_0 = lc(P->ctx,Q->c[0].v.r, Q->c[2].v.r, Q->c[1].v.r);
    Q->beta_1 = lc(P->ctx,Q->c[0].v.r, Q->c[1].v.r, Q->c[2].v.r);
    Q->beta_2 = M_PI - Q->beta_0;
    Q->c[0].p.y = Q->c[2].v.r * sin(Q->beta_0);
    Q->c[1].p.y = Q->c[0].p.y;
    Q->p.y = 2. * Q->c[0].p.y;
    Q->c[2].p.y = 0.;
    Q->c[1].p.x = 0.5 * Q->c[0].v.r;
    Q->c[0].p.x = -Q->c[1].p.x;
    Q->c[2].p.x = Q->c[0].p.x + Q->c[2].v.r * cos(Q->beta_0);
    Q->p.x = Q->c[2].p.x;

    P->es = 0.;
    P->fwd = chamb_s_forward;

    return P;
}