Function pj_ellipsoid

ThirdParty/libproj/vtklibproj/src/ell_set.cpp:23–131

/

/***************************************************************************************/
int pj_ellipsoid (PJ *P) {
/****************************************************************************************
    This is a replacement for the classic PROJ pj_ell_set function. The main difference
    is that pj_ellipsoid augments the PJ object with a copy of the exact tags used to
    define its related ellipsoid.

    This makes it possible to let a new PJ object inherit the geometrical properties
    of an existing one.

    A complete ellipsoid definition comprises a size (primary) and a shape (secondary)
    parameter.

    Size parameters supported are:
        R, defining the radius of a spherical planet
        a, defining the semimajor axis of an ellipsoidal planet

    Shape parameters supported are:
        rf, the reverse flattening of the ellipsoid
        f,  the flattening of the ellipsoid
        es, the eccentricity squared
        e,  the eccentricity
        b,  the semiminor axis

    The ellps=xxx parameter provides both size and shape for a number of built in
    ellipsoid definitions.

    The ellipsoid definition may be augmented with a spherification flag, turning
    the ellipsoid into a sphere with features defined by the ellipsoid.

    Spherification parameters supported are:
        R_A, which gives a sphere with the same surface area as the ellipsoid
        R_A, which gives a sphere with the same volume as the ellipsoid

        R_a, which gives a sphere with R = (a + b)/2   (arithmetic mean)
        R_g, which gives a sphere with R = sqrt(a*b)   (geometric mean)
        R_h, which gives a sphere with R = 2*a*b/(a+b) (harmonic mean)

        R_lat_a=phi, which gives a sphere with R being the arithmetic mean of
             of the corresponding ellipsoid at latitude phi.
        R_lat_g=phi, which gives a sphere with R being the geometric mean of
             of the corresponding ellipsoid at latitude phi.

    If R is given as size parameter, any shape and spherification parameters
    given are ignored.

    If size and shape are given as ellps=xxx, later shape and size parameters
    are are taken into account as modifiers for the built in ellipsoid definition.

    While this may seem strange, it is in accordance with historical PROJ
    behavior. It can e.g. be used to define coordinates on the ellipsoid
    scaled to unit semimajor axis by specifying "+ellps=xxx +a=1"

****************************************************************************************/
    int err = proj_errno_reset (P);
    const char *empty = {""};

    free(P->def_size);
    P->def_size = nullptr;