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Annotation of researchv10no/cmd/map/libmap/perspective.c, revision 1.1

1.1     ! root        1: #include "map.h"
        !             2: 
        !             3: #define ORTHRAD 1000
        !             4: static double viewpt;
        !             5: 
        !             6: static int
        !             7: Xperspective(struct place *place, double *x, double *y)
        !             8: {
        !             9:        double r;
        !            10:        if(viewpt<=1+FUZZ && fabs(place->nlat.s<=viewpt+.01))
        !            11:                return(-1);
        !            12:        r = place->nlat.c*(viewpt - 1.)/(viewpt - place->nlat.s);
        !            13:        *x = - r*place->wlon.s;
        !            14:        *y = - r*place->wlon.c;
        !            15:        if(r>4.)
        !            16:                return(-1);
        !            17:        if(fabs(viewpt)>1 && place->nlat.s<1/viewpt ||
        !            18:           fabs(viewpt)<=1 && place->nlat.s<viewpt)
        !            19:                        return 0;
        !            20:        return(1);
        !            21: }
        !            22: 
        !            23: proj
        !            24: perspective(double radius)
        !            25: {
        !            26:        viewpt = radius;
        !            27:        if(viewpt >= ORTHRAD)
        !            28:                return(Xorthographic);
        !            29:        if(fabs(viewpt-1.)<.0001)
        !            30:                return(0);
        !            31:        return(Xperspective);
        !            32: }
        !            33: 
        !            34:        /* called from various conformal projections,
        !            35:            but not from stereographic itself */
        !            36: int
        !            37: Xstereographic(struct place *place, double *x, double *y)
        !            38: {
        !            39:        double v = viewpt;
        !            40:        int retval;
        !            41:        viewpt = -1;
        !            42:        retval = Xperspective(place, x, y);
        !            43:        viewpt = v;
        !            44:        return retval;
        !            45: }
        !            46: 
        !            47: proj
        !            48: stereographic(void)
        !            49: {
        !            50:        viewpt = -1.;
        !            51:        return(Xperspective);
        !            52: }
        !            53: 
        !            54: proj
        !            55: gnomonic(void)
        !            56: {
        !            57:        viewpt = 0.;
        !            58:        return(Xperspective);
        !            59: }
        !            60: 
        !            61: int
        !            62: plimb(double *lat, double *lon, double res)
        !            63: {
        !            64:        static first = 1;
        !            65:        if(viewpt >= ORTHRAD)
        !            66:                return olimb(lat, lon, res);
        !            67:        if(first) {
        !            68:                first = 0;
        !            69:                *lon = -180;
        !            70:                if(fabs(viewpt) < .01)
        !            71:                        *lat = 0;
        !            72:                else if(fabs(viewpt)<=1)
        !            73:                        *lat = asin(viewpt)/RAD;
        !            74:                else
        !            75:                        *lat = asin(1/viewpt)/RAD;
        !            76:        } else
        !            77:                *lon += res;
        !            78:        if(*lon <= 180)
        !            79:                return 1;
        !            80:        first = 1;
        !            81:        return -1;
        !            82: }

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