/** \brief Transform boundary, taking into account 3D coordinates.
 *
 * Transform boundary densifying the edges to account for nonlinear
 * transformations along these edges and extracting the outermost bounds.
 *
 * Note that the current implementation is not "perfect" when the source CRS is
 * geocentric, the target CRS is geographic, and the input bounding box
 * includes the center of the Earth, a pole or the antimeridian. In those
 * circumstances, exact values of the latitude of longitude of discontinuity
 * will not be returned.
 *
 * If one of the source or target CRS of the transformation is not 3D, the
 * values of *out_zmin / *out_zmax may not be significant.
 *
 * For 2D or "2.5D" transformation (that is planar component is
 * geographic/coordinates and 3D axis is elevation), the documentation of
 * proj_trans_bounds() applies.
 *
 * @param context The PJ_CONTEXT object.
 * @param P The PJ object representing the transformation.
 * @param direction The direction of the transformation.
 * @param xmin Minimum bounding coordinate of the first axis in source CRS
 *             (target CRS if direction is inverse).
 * @param ymin Minimum bounding coordinate of the second axis in source CRS.
 *             (target CRS if direction is inverse).
 * @param zmin Minimum bounding coordinate of the third axis in source CRS.
 *             (target CRS if direction is inverse).
 * @param xmax Maximum bounding coordinate of the first axis in source CRS.
 *             (target CRS if direction is inverse).
 * @param ymax Maximum bounding coordinate of the second axis in source CRS.
 *             (target CRS if direction is inverse).
 * @param zmax Maximum bounding coordinate of the third axis in source CRS.
 *             (target CRS if direction is inverse).
 * @param out_xmin Minimum bounding coordinate of the first axis in target CRS
 *             (source CRS if direction is inverse).
 * @param out_ymin Minimum bounding coordinate of the second axis in target CRS.
 *             (source CRS if direction is inverse).
 * @param out_zmin Minimum bounding coordinate of the third axis in target CRS.
 *             (source CRS if direction is inverse).
 * @param out_xmax Maximum bounding coordinate of the first axis in target CRS.
 *             (source CRS if direction is inverse).
 * @param out_ymax Maximum bounding coordinate of the second axis in target CRS.
 *             (source CRS if direction is inverse).
 * @param out_zmax Maximum bounding coordinate of the third axis in target CRS.
 *             (source CRS if direction is inverse).
 * @param densify_pts Recommended to use 21. This is the number of points
 *     to use to densify the bounding polygon in the transformation.
 * @return an integer. 1 if successful. 0 if failures encountered.
 * @since 9.6
 */