/// <summary>
/// Provides all of the unidirectional edges from the current H3Index.
/// </summary>
/// <param name="origin">The origin hexagon H3Index to find edges for.</param>
/// <param name="edges">The memory to store all of the edges inside.</param>
/// <!-- Based off 3.1.1 -->
public static void getH3UnidirectionalEdgesFromHexagon(H3Index origin,
List <H3Index> edges)
{
// Determine if the origin is a pentagon and special treatment needed.
int isPentagon = H3Index.h3IsPentagon(origin);
// This is actually quite simple. Just modify the bits of the origin
// slightly for each direction, except the 'k' direction in pentagons,
// which is zeroed.
for (int i = 0; i < 6; i++)
{
if (isPentagon != 0 && i == 0)
{
edges[i] = H3Index.H3_INVALID_INDEX;
}
else
{
edges[i] = origin;
var ei = edges[i];
H3Index.H3_SET_MODE(ref ei, Constants.H3_UNIEDGE_MODE);
H3Index.H3_SET_RESERVED_BITS(ref ei, (ulong)i + 1);
edges[i] = ei;
}
}
}
/// <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 origin hexagon from the unidirectional edge H3Index
/// </summary>
/// <param name="edge">The edge H3 index</param>
/// <returns>The origin H3 hexagon index</returns>
/// <!-- Based off 3.1.1 -->
public static H3Index getOriginH3IndexFromUnidirectionalEdge(H3Index edge)
{
if (H3Index.H3_GET_MODE(ref edge) != Constants.H3_UNIEDGE_MODE)
{
return(H3Index.H3_INVALID_INDEX);
}
H3Index origin = edge.value;
H3Index.H3_SET_MODE(ref origin, Constants.H3_HEXAGON_MODE);
H3Index.H3_SET_RESERVED_BITS(ref origin, 0);
return(origin);
}
