@loaders.gl/geoarrow
Version:
GeoArrow columnar geometry encoding and decoding
125 lines (124 loc) • 3.98 kB
JavaScript
// loaders.gl
// SPDX-License-Identifier: MIT
// Copyright (c) vis.gl contributors
import * as arrow from 'apache-arrow';
/**
* Examines a column containing GeoArrow formatted data and returns information about the geometry type
* that can be useful during traversal
* @see https://geoarrow.org/format.html#memory-layouts
*/
// eslint-disable-next-line max-statements
export function getGeoArrowGeometryInfo(arrowField) {
if (arrowField.type instanceof arrow.Utf8) {
return {
compatibleEncodings: ['geoarrow.wkt'],
nesting: 0,
/** @note: Dimension encoded in WKT */
dimension: 2,
coordinates: 'interleaved',
valueType: 'double'
};
}
if (arrowField.type instanceof arrow.Binary || arrowField.type instanceof arrow.LargeBinary) {
return {
compatibleEncodings: ['geoarrow.wkb'],
nesting: 0,
/** @note: Dimension encoded in WKB */
dimension: 2,
coordinates: 'interleaved',
valueType: 'double'
};
}
let coordinateInfo = getCoordinateFieldInfo(arrowField);
// A point is just a Coordinate
if (coordinateInfo) {
return {
compatibleEncodings: ['geoarrow.point'],
nesting: 0,
...coordinateInfo
};
}
// A line string or a multipoint is a List<Coordinate>
if (!(arrowField.type instanceof arrow.List)) {
return null;
}
arrowField = arrowField.type.children[0];
coordinateInfo = getCoordinateFieldInfo(arrowField);
if (coordinateInfo) {
return {
compatibleEncodings: ['geoarrow.linestring', 'geoarrow.multipoint'],
nesting: 1,
...coordinateInfo
};
}
// A polygon or a multiline string are List<List<Coordinate>>
if (!(arrowField.type instanceof arrow.List)) {
return null;
}
arrowField = arrowField.type.children[0];
coordinateInfo = getCoordinateFieldInfo(arrowField);
if (coordinateInfo) {
return {
compatibleEncodings: ['geoarrow.polygon', 'geoarrow.multilinestring'],
nesting: 2,
...coordinateInfo
};
}
// A multipolygons are List<List<List<Coordinate>>>
if (!(arrowField.type instanceof arrow.List)) {
return null;
}
arrowField = arrowField.type.children[0];
coordinateInfo = getCoordinateFieldInfo(arrowField);
if (coordinateInfo) {
return {
compatibleEncodings: ['geoarrow.multipolygon'],
nesting: 3,
...coordinateInfo
};
}
return null;
}
/**
* @see https://geoarrow.org/format.html#memory-layouts
*/
function getCoordinateFieldInfo(arrowField) {
// interleaved case
if (arrowField.type instanceof arrow.FixedSizeList) {
const dimension = arrowField.type.listSize;
if (dimension < 2 || dimension > 4) {
return null;
}
const child = arrowField.type.children[0];
// Spec currently only supports 64 bit coordinates
if (!(child.type instanceof arrow.Float)) {
return null;
}
return {
coordinates: 'interleaved',
dimension: dimension,
valueType: 'double'
};
}
// separated case
if (arrowField.type instanceof arrow.Struct) {
const children = arrowField.type.children;
const dimension = children.length;
if (dimension < 2 || dimension > 4) {
return null;
}
// Spec currently only supports 64 bit coordinates
for (const child of children) {
if (!(child.type instanceof arrow.Float)) {
return null;
}
}
return {
coordinates: 'separated',
dimension: dimension,
valueType: 'double'
};
}
// No other types are valid coordinates
return null;
}