| 1 |
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| 2 | int XY_to_RD (double *ra, double *dec, double x, double y, psProjection *proj) {
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| 3 |
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| 4 | double sphi, cphi, stht, ctht;
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| 5 | double alpha, delta;
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| 6 |
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| 7 | double Ro = proj->R;
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| 8 | double Do = proj->D;
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| 9 |
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| 10 | double L = x * proj->Xs;
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| 11 | double M = y * proj->Ys;
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| 12 |
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| 13 | PseudoCyl = (proj->type == PS_PROJ_AIT) || (proj->type == PS_PROJ_PAR) || (proj->type == PS_PROJ_GLS);
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| 14 | Zenith1 = (proj->type == PS_PROJ_TAN);
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| 15 | Zenith2 = (proj->type == PS_PROJ_SIN);
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| 16 | Zenithal = Zenith1 || Zenith2;
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| 17 | if (!Zenithal && !PseudoCyl) return (FALSE);
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| 18 |
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| 19 | /**** Zenithal Projections ****/
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| 20 | if (Zenithal) {
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| 21 | double R = hypot (L,M);
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| 22 | if ((L == 0) && (M == 0)) {
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| 23 | sphi = 0;
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| 24 | cphi = 1;
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| 25 | } else {
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| 26 | sphi = L / R;
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| 27 | cphi = -M / R;
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| 28 | }
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| 29 |
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| 30 | if (Zenith1) {
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| 31 | if (R == 0) {
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| 32 | stht = 1.0;
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| 33 | ctht = 0.0;
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| 34 | } else {
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| 35 | double T = 1.0 / R;
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| 36 | stht = T / sqrt ( 1.0 + T*T);
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| 37 | ctht = 1.0 / sqrt ( 1.0 + T*T);
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| 38 | }
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| 39 | }
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| 40 | if (Zenith2) {
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| 41 | ctht = R;
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| 42 | stht = sqrt (1 - ctht*ctht);
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| 43 | }
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| 44 | if (!strcmp(type, "-ZEA")) {
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| 45 | stht = 1 - 0.5*SQ(R);
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| 46 | ctht = sqrt (1 - stht*stht);
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| 47 | }
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| 48 |
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| 49 | double sdp = sin(Do);
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| 50 | double cdp = cos(Do);
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| 51 |
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| 52 | double sdel = stht*sdp - ctht*cphi*cdp;
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| 53 | double salp = ctht*sphi;
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| 54 | double calp = stht*cdp + ctht*cphi*sdp;
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| 55 | alpha = atan2 (salp, calp);
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| 56 | delta = asin (sdel);
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| 57 |
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| 58 | *ra = alpha + Ro;
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| 59 | *dec = delta;
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| 60 | return (TRUE);
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| 61 | }
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| 62 |
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| 63 | /**** Other Conventional Projections ****/
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| 64 | if (PseudoCyl) {
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| 65 | if (proj->type === PS_PROJ_AIT) {
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| 66 | double Z2 = (1.0 - SQ(0.25*L) - SQ(0.5*M));
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| 67 | if (Z2 < 0) return (FALSE);
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| 68 |
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| 69 | double Z = sqrt (Z2);
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| 70 | alpha = 2.0 * atan2 (0.5*Z*L, 2.0*Z2 - 1.0);
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| 71 | delta = asin (M*Z);
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| 72 | }
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| 73 | if (proj->type === PS_PROJ_GLS) {
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| 74 | alpha = L / cos (M);
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| 75 | delta = M;
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| 76 | }
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| 77 | if (proj->type === PS_PROJ_PAR) {
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| 78 | alpha = L / (1.0 - SQ(2.0*M/M_PI));
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| 79 | delta = 3 * asin (M/M_PI);
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| 80 | }
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| 81 |
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| 82 | *ra = alpha + Ro;
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| 83 | *dec = delta + Do;
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| 84 | return (TRUE);
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| 85 | }
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| 86 | }
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