/// <summary>
/// Returns a unidirectional edge H3 index based on the provided origin and
/// destination
/// </summary>
/// <param name="origin">The origin H3 hexagon index</param>
/// <param name="destination">The destination H3 hexagon index</param>
/// <returns>The unidirectional edge H3Index, or 0 on failure.</returns>
/// <!-- Based off 3.1.1 -->
public static H3Index getH3UnidirectionalEdge(H3Index origin, H3Index destination)
{
// Short-circuit and return an invalid index value if they are not neighbors
if (h3IndexesAreNeighbors(origin, destination) == 0)
{
return(H3Index.H3_INVALID_INDEX);
}
// Otherwise, determine the IJK direction from the origin to the destination
H3Index output = origin;
H3Index.H3_SET_MODE(ref output, Constants.H3_UNIEDGE_MODE);
// Checks each neighbor, in order, to determine which direction the
// destination neighbor is located. Skips CENTER_DIGIT since that
// would be this index.
for (var direction = Direction.K_AXES_DIGIT;
direction < Direction.NUM_DIGITS;
direction++)
{
int rotations = 0;
H3Index neighbor = Algos.h3NeighborRotations(origin, direction, ref rotations);
if (neighbor == destination)
{
H3Index.H3_SET_RESERVED_BITS(ref output, (ulong)direction);
return(output);
}
}
// This should be impossible, return an invalid H3Index in this case;
return(H3Index.H3_INVALID_INDEX); // LCOV_EXCL_LINE
}
/// <summary>
/// Returns the destination hexagon from the unidirectional edge H3Index
/// </summary>
/// <param name="edge">The edge H3 index</param>
/// <returns>The destination H3 hexagon index</returns>
/// <!-- Based off 3.1.1 -->
public static H3Index getDestinationH3IndexFromUnidirectionalEdge(H3Index edge)
{
if (H3Index.H3_GET_MODE(ref edge) != Constants.H3_UNIEDGE_MODE)
{
return(H3Index.H3_INVALID_INDEX);
}
Direction direction = (Direction)H3Index.H3_GET_RESERVED_BITS(edge);
int rotations = 0;
H3Index destination = Algos
.h3NeighborRotations
(
getOriginH3IndexFromUnidirectionalEdge(edge),
direction,
ref rotations
);
return(destination);
}