NAME
Geo::H3::FFI - Perl FFI binding to H3 library functions
SYNOPSIS
use Geo::H3::FFI;
DESCRIPTION
Perl FFI binding to H3 library functions
CONSTRUCTORS
new
my $gh3 = Geo::H3::FFI->new;
geo
Returns a GeoCoord struct
my $geo = $gh3->geo; #empty struct #isa Geo::H3::FFI::Struct::GeoCoord
my $geo = $gh3->geo(lat=>$lat_rad, lon=>$lon_rad); #isa Geo::H3::FFI::Struct::GeoCoord
gb
Returns a GeoBoundary struct
my $gb = $gh3->gb; #empty struct #isa Geo::H3::FFI::Struct::GeoBoundary
Indexing Functions
These function are used for finding the H3 index containing coordinates,
and for finding the center and boundary of H3 indexes.
geoToH3
Indexes the location at the specified resolution, returning the index of
the cell containing the location.
my $geo = $gh3->geo(lat=>$lat_rad, lon=>$lon_rad); #isa Geo::H3::FFI::Struct::GeoCoord
my $resolution = 8; #isa Int in (0 .. 15)
my $index = $gh3->geoToH3($geo, $resolution); #isa Int64
Returns 0 on error.
geoToH3Wrapper
my $index = $gh3->geoToH3Wrapper(lat=>$lat_rad, lon=>$lon_rad, resolution=>$resolution);
my $index = $gh3->geoToH3Wrapper(lat=>$lat, lon=>$lon, resolution=>$resolution, uom=>"deg");
h3ToGeo
Finds the centroid of the index.
my $geo = $gh3->geo; #isa Geo::H3::FFI::Struct::GeoCoord
$gh3->h3ToGeo($index, $geo);
my $lat = $geo->lat; #isa Float in radians
my $lon = $geo->lon; #isa Float in radians
h3ToGeoWrapper
my $geo = h3ToGeoWrapper($index); #isa Geo::H3::FFI::Struct::GeoCoord
my $lat = $geo->lat; #isa Float in radians
my $lon = $geo->lon; #isa Float in radians
h3ToGeoBoundary
Finds the boundary of the index.
my $gb = $gh3->gb; #isa empty Geo::H3::FFI::Struct::GeoBoundary
$gh3->h3ToGeoBoundary($index, $gb); #populates $gb
my $num_verts = $gb->num_verts; #isa Int
my $vert0 = $gb->verts->[0]; #isa Geo::H3::FFI::Struct::GeoCord
h3ToGeoBoundaryWrapper
my $GeoBoundary = $gh3->h3ToGeoBoundaryWrapper($index); #isa Geo::H3::FFI::Struct::GeoBoundary
Index Inspection Functions
These functions provide metadata about an H3 index, such as its
resolution or base cell, and provide utilities for converting into and
out of the 64-bit representation of an H3 index.
h3GetResolution
Returns the resolution of the index.
my $resolution = $gh3->h3GetResolution($index); #isa Int
h3GetBaseCell
Returns the base cell number of the index.
my $baseCell = h3GetBaseCell($index);
stringToH3
Converts the string representation to H3Index (uint64_t) representation.
Returns 0 on error.
my $index = $gh3->stringToH3($string, length($string));
stringToH3Wrapper
my $index = $gh3->stringToH3Wrapper($string);
h3ToString
Converts the H3Index representation of the index to the string
representation. str must be at least of length 17.
my $size = 17; #Must be 17 for API to work
my $string = "\000" x $size;
$gh3->h3ToString($index, $string, $size);
$string =~ s/\000+\Z//;
h3ToStringWrapper
my $string = $gh3->h3ToStringWrapper($index);
h3IsValid
Returns non-zero if this is a valid H3 index.
my isValid = $gh3->h3IsValid($index);
h3IsResClassIII
Returns non-zero if this index has a resolution with Class III
orientation.
my $isRC3 = $gh3->h3IsResClassIII($index);
h3IsPentagon
Returns non-zero if this index represents a pentagonal cell.
my $isPentagon = $gh3->h3IsPentagon($index);
h3GetFaces
Find all icosahedron faces intersected by a given H3 index and places
them in the array out. out must be at least of length maxFaceCount(h).
Faces are represented as integers from 0-19, inclusive. The array is
sparse, and empty (no intersection) array values are represented by -1.
my @array = (-1,-1,-1,-1,-1);
$gh3->h3GetFaces($index, \@array); #sets values into initialized array
h3GetFacesWrapper
my $array_ref = $gh3->h3GetFacesWrapper($index);
maxFaceCount
Returns the maximum number of icosahedron faces the given H3 index may
intersect.
my $count = $gh3->maxFaceCount($index);
Grid traversal functions
Grid traversal allows finding cells in the vicinity of an origin cell,
and determining how to traverse the grid from one cell to another.
kRing
k-rings produces indices within k distance of the origin index.
k-ring 0 is defined as the origin index, k-ring 1 is defined as k-ring 0
and all neighboring indices, and so on.
Output is placed in the provided array in no particular order. Elements
of the output array may be left zero, as can happen when crossing a
pentagon.
my $size = $gh3->maxKringSize($k);
my @array = (-1) x $size;
$self->kRing($index, $k, \@array);
kRingWrapper
Returns an array reference of H3 indices with the k distance of the
origin index.
my $aref = $gh3->kRingWrapper($index, $k); #ias ARRAY of H3 Indexes
maxKringSize
Maximum number of indices that result from the kRing algorithm with the
given k.
my $size = $gh3->maxKringSize($k);
kRingDistances
k-rings produces indices within k distance of the origin index.
k-ring 0 is defined as the origin index, k-ring 1 is defined as k-ring 0
and all neighboring indices, and so on.
Output is placed in the provided array in no particular order. Elements
of the output array may be left zero, as can happen when crossing a
pentagon.
my $size = $gh3->maxKringSize($k);
my @array = (-1) x $size;
my @dist = (-1) x $size;
my %hash = ();
$gh3->kRingDistances($index, $k, \@array, \@dist);
kRingDistancesWrapper
Returns a hash reference where the keys are the H3 index and values are
the k distance for the given index and k value.
my $href = $gh3->kRingDistancesWrapper($index, $k); #isa HASH
hexRange
hexRange produces indexes within k distance of the origin index. Output
behavior is undefined when one of the indexes returned by this function
is a pentagon or is in the pentagon distortion area.
k-ring 0 is defined as the origin index, k-ring 1 is defined as k-ring 0
and all neighboring indexes, and so on.
Output is placed in the provided array in order of increasing distance
from the origin.
Returns 0 if no pentagonal distortion is encountered.
my $return = $gh3->hexRange($index, $k, \@out);
hexRangeWrapper
my @indexes = $gh3->hexRangeWrapper($index, $k);
maxHexRangeSize
my $size = $gh3->maxHexRangeSize($k);
hexRangeDistances
hexRange produces indexes within k distance of the origin index. Output
behavior is undefined when one of the indexes returned by this function
is a pentagon or is in the pentagon distortion area.
k-ring 0 is defined as the origin index, k-ring 1 is defined as k-ring 0
and all neighboring indexes, and so on.
Output is placed in the provided array in order of increasing distance
from the origin. The distances in hexagons is placed in the distances
array at the same offset.
Returns 0 if no pentagonal distortion is encountered.
my $return = $gh3->hexRangeDistances($index, $k, \@indexes, \@distances);
hexRangeDistancesWrapper
my $href = $gh3->hexRangeDistancesWrapper($index, $k);
hexRanges
hexRanges takes an array of input hex IDs and a max k-ring and returns
an array of hexagon IDs sorted first by the original hex IDs and then by
the k-ring (0 to max), with no guaranteed sorting within each k-ring
group.
Returns 0 if no pentagonal distortion was encountered. Otherwise, output
is undefined
hexRing
Produces the hollow hexagonal ring centered at origin with sides of
length k.
Returns 0 if no pentagonal distortion was encountered.
my $distortion = $gh3->hexRing($index, $k, \@ring);
hexRingWrapper
my $aref = $gh3->hexRingWrapper($index, $k);
maxHexRingSize
my $size = $gh3->maxHexRingSize($k);
h3Line
Given two H3 indexes, return the line of indexes between them
(inclusive).
This function may fail to find the line between two indexes, for example
if they are very far apart. It may also fail when finding distances for
indexes on opposite sides of a pentagon.
Notes:
- The specific output of this function should not be considered stable across library versions. The only guarantees the library provides are that the line length will be h3Distance(start, end) + 1 and that every index in the line will be a neighbor of the preceding index.
- Lines are drawn in grid space, and may not correspond exactly to either Cartesian lines or great arcs.
h3LineWrapper
my $aref = $gh3->h3LineWrapper($start, $end);
h3LineSize
Number of indexes in a line from the start index to the end index, to be
used for allocating memory. Returns a negative number if the line cannot
be computed.
h3Distance
Returns the distance in grid cells between the two indexes.
Returns a negative number if finding the distance failed. Finding the
distance can fail because the two indexes are not comparable (different
resolutions), too far apart, or are separated by pentagonal distortion.
This is the same set of limitations as the local IJ coordinate space
functions.
experimentalH3ToLocalIj
Produces local IJ coordinates for an H3 index anchored by an origin.
This function is experimental, and its output is not guaranteed to be
compatible across different versions of H3.
experimentalLocalIjToH3
Produces an H3 index from local IJ coordinates anchored by an origin.
This function is experimental, and its output is not guaranteed to be
compatible across different versions of H3.
Hierarchical grid functions
These functions permit moving between resolutions in the H3 grid system.
The functions produce parent (coarser) or children (finer) cells.
h3ToParent
Returns the parent (coarser) index containing h.
my $parent = $gh3->h3ToParent($index, $resolution);
h3ToChildren
Populates children with the indexes contained by h at resolution
childRes. children must be an array of at least size
maxH3ToChildrenSize(h, childRes).
my $size = $gh3->maxH3ToChildrenSize($index, $res);
my @array = (-1) x $size;
$gh3->h3ToChildren($index, $res, \@array);
h3ToChildrenWrapper
my $aref = $gh3->h3ToChildrenWrapper($index, $resoultion);
maxH3ToChildrenSize
my $size = $gh3->maxH3ToChildrenSize($index, $res);
h3ToCenterChild
Returns the center child (finer) index contained by h at resolution
childRes.
compact
Compacts the set h3Set of indexes as best as possible, into the array
compactedSet. compactedSet must be at least the size of h3Set in case
the set cannot be compacted.
Returns 0 on success.
compactWrapper
my $aref = $gh3->compactWrapper(\@indexes);
uncompact
Uncompacts the set compactedSet of indexes to the resolution res. h3Set
must be at least of size maxUncompactSize(compactedSet, numHexes, res).
Returns 0 on success.
maxUncompactSize
Returns the size of the array needed by uncompact.
Region functions
These functions convert H3 indexes to and from polygonal areas.
polyfill
polyfill takes a given GeoJSON-like data structure and preallocated,
zeroed memory, and fills it with the hexagons that are contained by the
GeoJSON-like data structure.
Containment is determined by the cells' centroids. A partioning using
the GeoJSON-like data structure, where polygons cover an area without
overlap, will result in a partitioning in the H3 grid, where cells cover
the same area without overlap.
maxPolyfillSize
maxPolyfillSize returns the number of hexagons to allocate space for
when performing a polyfill on the given GeoJSON-like data structure.
h3SetToLinkedGeo
Create a LinkedGeoPolygon describing the outline(s) of a set of
hexagons. Polygon outlines will follow GeoJSON MultiPolygon order: Each
polygon will have one outer loop, which is first in the list, followed
by any holes.
It is the responsibility of the caller to call destroyLinkedPolygon on
the populated linked geo structure, or the memory for that structure
will not be freed.
It is expected that all hexagons in the set have the same resolution and
that the set contains no duplicates. Behavior is undefined if duplicates
or multiple resolutions are present, and the algorithm may produce
unexpected or invalid output.
h3SetToMultiPolygon
destroyLinkedPolygon
Free all allocated memory for a linked geo structure. The caller is
responsible for freeing memory allocated to the input polygon struct.
Unidirectional edge functions
Unidirectional edges allow encoding the directed edge from one cell to a
neighboring cell.
h3IndexesAreNeighbors
Returns whether or not the provided H3Indexes are neighbors.
Returns 1 if the indexes are neighbors, 0 otherwise.
getH3UnidirectionalEdge
Returns a unidirectional edge H3 index based on the provided origin and
destination.
Returns 0 on error.
h3UnidirectionalEdgeIsValid
Determines if the provided H3Index is a valid unidirectional edge index.
Returns 1 if it is a unidirectional edge H3Index, otherwise 0.
getOriginH3IndexFromUnidirectionalEdge
Returns the origin hexagon from the unidirectional edge H3Index.
getDestinationH3IndexFromUnidirectionalEdge
Returns the destination hexagon from the unidirectional edge H3Index.
getH3IndexesFromUnidirectionalEdge
Returns the origin, destination pair of hexagon IDs for the given edge
ID, which are placed at originDestination[0] and originDestination[1]
respectively.
getH3UnidirectionalEdgesFromHexagon
Provides all of the unidirectional edges from the current H3Index. edges
must be of length 6, and the number of undirectional edges placed in the
array may be less than 6.
getH3UnidirectionalEdgeBoundary
Provides the coordinates defining the unidirectional edge.
Miscellaneous H3 functions
These functions include descriptions of the H3 grid system.
degsToRads
Converts degrees to radians.
radsToDegs
Converts radians to degrees.
hexAreaKm2
Average hexagon area in square kilometers at the given resolution.
hexAreaM2
Average hexagon area in square meters at the given resolution.
cellAreaM2
Exact area of specific cell in square meters.
cellAreaRads2
Exact area of specific cell in square radians.
edgeLengthKm
Average hexagon edge length in kilometers at the given resolution.
edgeLengthM
Average hexagon edge length in meters at the given resolution.
exactEdgeLengthKm
Exact edge length of specific unidirectional edge in kilometers.
exactEdgeLengthM
Exact edge length of specific unidirectional edge in meters.
exactEdgeLengthRads
Exact edge length of specific unidirectional edge in radians.
numHexagons
Number of unique H3 indexes at the given resolution.
getRes0Indexes
All the resolution 0 H3 indexes. out must be an array of at least size
res0IndexCount().
res0IndexCount
Number of resolution 0 H3 indexes.
getPentagonIndexes
All the pentagon H3 indexes at the specified resolution. out must be an
array of at least size pentagonIndexCount().
pentagonIndexCount
Number of pentagon H3 indexes per resolution. This is always 12, but
provided as a convenience.
pointDistKm
Gives the "great circle" or "haversine" distance between pairs of
GeoCoord points (lat/lon pairs) in kilometers.
pointDistM
Gives the "great circle" or "haversine" distance between pairs of
GeoCoord points (lat/lon pairs) in meters.
pointDistRads
Gives the "great circle" or "haversine" distance between pairs of
GeoCoord points (lat/lon pairs) in radians.
SEE ALSO
,
, FFI::CheckLib,
FFI::Platypus, FFI::C
AUTHOR
Michael R. Davis
COPYRIGHT AND LICENSE
MIT License
Copyright (c) 2020 Michael R. Davis
Permission is hereby granted, free of charge, to any person obtaining a
copy of this software and associated documentation files (the
"Software"), to deal in the Software without restriction, including
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permit persons to whom the Software is furnished to do so, subject to
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The above copyright notice and this permission notice shall be included
in all copies or substantial portions of the Software.
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