Class: TopoJSON

ol/format/TopoJSON~TopoJSON 


import TopoJSON from 'ol/format/TopoJSON.js';

Feature format for reading data in the TopoJSON format.

new TopoJSON(options)

format/TopoJSON.js, line 57
Name Type Description
dataProjection ProjectionLike (defaults to 'EPSG:4326')

Default data projection.
layerName string | undefined

Set the name of the TopoJSON topology objects's children as feature property with the specified name. This means that when set to 'layer', a topology like

{
  "type": "Topology",
  "objects": {
    "example": {
      "type": "GeometryCollection",
      "geometries": []
    }
  }
}

will result in features that have a property 'layer' set to 'example'. When not set, no property will be added to features.
layers Array.<string> | undefined

Names of the TopoJSON topology's objects's children to read features from. If not provided, features will be read from all children.

Extends

Methods

readFeature(source, options){Feature} inherited

format/JSONFeature.js, line 36

Read a feature. Only works for a single feature. Use readFeatures to read a feature collection.

Name Type Description
source ArrayBuffer | Document | Element | Object | string

Source.
options

Read options.

Name Type Description
dataProjection ProjectionLike | undefined

Projection of the data we are reading. If not provided, the projection will be derived from the data (where possible) or the dataProjection of the format is assigned (where set). If the projection can not be derived from the data and if no dataProjection is set for a format, the features will not be reprojected.
extent Extent | undefined

Tile extent in map units of the tile being read. This is only required when reading data with tile pixels as geometry units. When configured, a dataProjection with TILE_PIXELS as units and the tile's pixel extent as extent needs to be provided.
featureProjection ProjectionLike | undefined

Projection of the feature geometries created by the format reader. If not provided, features will be returned in the dataProjection.
Returns:
Feature.

readFeatures(source, options){Array<Feature>} inherited

format/JSONFeature.js, line 52

Read all features. Works with both a single feature and a feature collection.

Name Type Description
source ArrayBuffer | Document | Element | Object | string

Source.
options

Read options.

Name Type Description
dataProjection ProjectionLike | undefined

Projection of the data we are reading. If not provided, the projection will be derived from the data (where possible) or the dataProjection of the format is assigned (where set). If the projection can not be derived from the data and if no dataProjection is set for a format, the features will not be reprojected.
extent Extent | undefined

Tile extent in map units of the tile being read. This is only required when reading data with tile pixels as geometry units. When configured, a dataProjection with TILE_PIXELS as units and the tile's pixel extent as extent needs to be provided.
featureProjection ProjectionLike | undefined

Projection of the feature geometries created by the format reader. If not provided, features will be returned in the dataProjection.
Returns:
Features.

readGeometry(source, options){Geometry} inherited

format/JSONFeature.js, line 89

Read a geometry.

Name Type Description
source ArrayBuffer | Document | Element | Object | string

Source.
options

Read options.

Name Type Description
dataProjection ProjectionLike | undefined

Projection of the data we are reading. If not provided, the projection will be derived from the data (where possible) or the dataProjection of the format is assigned (where set). If the projection can not be derived from the data and if no dataProjection is set for a format, the features will not be reprojected.
extent Extent | undefined

Tile extent in map units of the tile being read. This is only required when reading data with tile pixels as geometry units. When configured, a dataProjection with TILE_PIXELS as units and the tile's pixel extent as extent needs to be provided.
featureProjection ProjectionLike | undefined

Projection of the feature geometries created by the format reader. If not provided, features will be returned in the dataProjection.
Returns:
Geometry.

readProjection(source){Projection} inherited

format/JSONFeature.js, line 114

Read the projection.

Name Type Description
source ArrayBuffer | Document | Element | Object | string

Source.
Returns:
Projection.

writeFeature(feature, options){string} inherited

format/JSONFeature.js, line 136

Encode a feature as string.

Name Type Description
feature Feature

Feature.
options

Write options.

Name Type Description
dataProjection ProjectionLike | undefined

Projection of the data we are writing. If not provided, the dataProjection of the format is assigned (where set). If no dataProjection is set for a format, the features will be returned in the featureProjection.
featureProjection ProjectionLike | undefined

Projection of the feature geometries that will be serialized by the format writer. If not provided, geometries are assumed to be in the dataProjection if that is set; in other words, they are not transformed.
rightHanded boolean | undefined

When writing geometries, follow the right-hand rule for linear ring orientation. This means that polygons will have counter-clockwise exterior rings and clockwise interior rings. By default, coordinates are serialized as they are provided at construction. If true, the right-hand rule will be applied. If false, the left-hand rule will be applied (clockwise for exterior and counter-clockwise for interior rings). Note that not all formats support this. The GeoJSON format does use this property when writing geometries.
decimals number | undefined

Maximum number of decimal places for coordinates. Coordinates are stored internally as floats, but floating-point arithmetic can create coordinates with a large number of decimal places, not generally wanted on output. Set a number here to round coordinates. Can also be used to ensure that coordinates read in can be written back out with the same number of decimals. Default is no rounding.
Returns:
Encoded feature.

writeFeatures(features, options){string} inherited

format/JSONFeature.js, line 158

Encode an array of features as string.

Name Type Description
features Array<Feature>

Features.
options

Write options.

Name Type Description
dataProjection ProjectionLike | undefined

Projection of the data we are writing. If not provided, the dataProjection of the format is assigned (where set). If no dataProjection is set for a format, the features will be returned in the featureProjection.
featureProjection ProjectionLike | undefined

Projection of the feature geometries that will be serialized by the format writer. If not provided, geometries are assumed to be in the dataProjection if that is set; in other words, they are not transformed.
rightHanded boolean | undefined

When writing geometries, follow the right-hand rule for linear ring orientation. This means that polygons will have counter-clockwise exterior rings and clockwise interior rings. By default, coordinates are serialized as they are provided at construction. If true, the right-hand rule will be applied. If false, the left-hand rule will be applied (clockwise for exterior and counter-clockwise for interior rings). Note that not all formats support this. The GeoJSON format does use this property when writing geometries.
decimals number | undefined

Maximum number of decimal places for coordinates. Coordinates are stored internally as floats, but floating-point arithmetic can create coordinates with a large number of decimal places, not generally wanted on output. Set a number here to round coordinates. Can also be used to ensure that coordinates read in can be written back out with the same number of decimals. Default is no rounding.
Returns:
Encoded features.

writeGeometry(geometry, options){string} inherited

format/JSONFeature.js, line 180

Encode a geometry as string.

Name Type Description
geometry Geometry

Geometry.
options

Write options.

Name Type Description
dataProjection ProjectionLike | undefined

Projection of the data we are writing. If not provided, the dataProjection of the format is assigned (where set). If no dataProjection is set for a format, the features will be returned in the featureProjection.
featureProjection ProjectionLike | undefined

Projection of the feature geometries that will be serialized by the format writer. If not provided, geometries are assumed to be in the dataProjection if that is set; in other words, they are not transformed.
rightHanded boolean | undefined

When writing geometries, follow the right-hand rule for linear ring orientation. This means that polygons will have counter-clockwise exterior rings and clockwise interior rings. By default, coordinates are serialized as they are provided at construction. If true, the right-hand rule will be applied. If false, the left-hand rule will be applied (clockwise for exterior and counter-clockwise for interior rings). Note that not all formats support this. The GeoJSON format does use this property when writing geometries.
decimals number | undefined

Maximum number of decimal places for coordinates. Coordinates are stored internally as floats, but floating-point arithmetic can create coordinates with a large number of decimal places, not generally wanted on output. Set a number here to round coordinates. Can also be used to ensure that coordinates read in can be written back out with the same number of decimals. Default is no rounding.
Returns:
Encoded geometry.