JSONFG -- OGC Features and Geometries JSON

Added in version 3.8.

Driver short name

JSONFG

Driver built-in by default

This driver is built-in by default

This driver implements read/write support for access to features encoded in OGC Features and Geometries JSON - Part 1: Core format.

JSON-FG is a set of extensions over the GeoJSON format.

The following extensions are supported:

capturing the feature type in a featureType element to affect features to separate
capturing a coordinate reference system (not necessarily WGS 84) in a coordRefSys element, that is the one used by geometries written in the place element
time element at Feature level
minimum support for Polyhedron geometries (with a single outer shell) and Prism with Point, LineString or Polygon base.

警告

This driver implements a draft version of the standard.

Driver capabilities

Supports Create()

This driver supports the GDALDriver::Create() operation

Supports Georeferencing

This driver supports georeferencing

Supports VirtualIO

This driver supports virtual I/O operations (/vsimem/, etc.)

Connection string

The JSON-FG driver accepts three types of sources of data:

Uniform Resource Locator (URL) - a Web address to perform HTTP request
Plain text file with JSON-FG data, typically with a .json extension
Text passed directly and encoded in JSON-FG

The URL/filename/text might be prefixed with JSONFG: to avoid any ambiguity with other drivers. Alternatively, starting with GDAL 3.10, specifying the -if JSONFG option to command line utilities accepting it, or JSONFG as the only value of the papszAllowedDrivers of GDALOpenEx(), also forces the driver to recognize the passed URL/filename/text.

Time support

On reading:

Feature.time.date elements are mapped to a OGR time field of type Date. If there is a property also called time, the OGR field for Feature.time is called jsonfg_time
Feature.time.timestamp elements are mapped to a OGR time field of type DateTime
Feature.time.interval elements are mapped to a OGR time_start and time_end fields of type Date or DateTime. If there are properties with those names, the OGR fields for Feature.time are prefixed with jsonfg_ Unbounded intervals (..) are mapped to a unset OGR feature field.

On writing, if fields called time, time_start, time_end of type Date or DateTime are created, their content is used to set the Feature.time element with the reverse logic as the above explained reading side. The field names may also be prefixed with jsonfg_ to distinguish them from fields time, time_start, time_end that must be written in Feature.properties

Configuration options

Configuration options can be specified in command-line tools using the syntax --config <NAME>=<VALUE> or using functions such as CPLSetConfigOption() (C) or gdal.config_options (Python). The following configuration options are available:

OGR_JSONFG_MAX_OBJ_SIZE=<MBytes>: Defaults to 200. size in MBytes of the maximum accepted single feature, or 0 to allow for a unlimited size (GDAL >= 3.5.2).

Open options

Open options can be specified in command-line tools using the syntax -oo <NAME>=<VALUE> or by providing the appropriate arguments to GDALOpenEx() (C) or gdal.OpenEx (Python). The following open options are supported:

GEOMETRY_ELEMENT=[AUTO/PLACE/GEOMETRY]: Defaults to AUTO. Determines which JSON element to use to create geometry from. By default when the place element is set, geometries are created from its content. And when it is absent or null, the content of the geometry element is used. Setting this option to PLACE restricts the reading to the place elements. Setting this option to GEOMETRY restricts the reading to the geometry elements.

Dataset creation options

Dataset creation options can be specified in command-line tools using the syntax -dsco <NAME>=<VALUE> or by providing the appropriate arguments to GDALCreate() (C) or Driver.Create (Python). The following dataset creation options are supported:

SINGLE_LAYER=[YES/NO]: Defaults to NO. Whether a single layer will be written. If set to YES, the coordRefSys and featureType elements can be written at the FeatureCollection level instead inside each Feature.

Layer creation options

Layer creation options can be specified in command-line tools using the syntax -lco <NAME>=<VALUE> or by providing the appropriate arguments to GDALDatasetCreateLayer() (C) or Dataset.CreateLayer (Python). The following layer creation options are supported:

COORDINATE_PRECISION_GEOMETRY=<integer>: Defaults to 7. Maximum number of figures after decimal separator to write in coordinates of geometry element.
COORDINATE_PRECISION_PLACE=<integer>: Maximum number of figures after decimal separator to write in coordinates of place element.
SIGNIFICANT_FIGURES=<integer>: Defaults to 17. Maximum number of significant figures when writing floating-point numbers. If explicitly specified, and COORDINATE_PRECISION_GEOMETRY or COORDINATE_PRECISION_PLACE is not, this will also apply to coordinates.
WRITE_GEOMETRY=[YES/NO]: Defaults to YES. By default, when a non-WGS 84 CRS is assigned to the layer, the geometry is written in the place element, and a reprojected version of it to WGS 84 is written in the geometry element. This option can be set to NO to avoid writing the geometry element when place is written. Setting this option to NO has no effect if the layer CRS is WGS 84, in which case geometries must be written in geometry.
ID_FIELD=value: Name of the source field that must be written as the 'id' member of Feature objects.
ID_TYPE=[AUTO/String/Integer]: Type of the 'id' member of Feature objects.
ID_GENERATE=[YES/NO]: Auto-generate feature ids

VSI Virtual File System API support

The driver supports reading and writing to files managed by VSI Virtual File System API, which includes "regular" files, as well as files in the /vsizip/ (read-write), /vsigzip/ (read-write), /vsicurl/ (read-only) domains.

Writing to /dev/stdout or /vsistdout/ is also supported.

Geometry coordinate precision

Added in version GDAL: 3.9

The GeoJSON driver supports reading and writing the geometry coordinate precision, using the OGRGeomCoordinatePrecision settings of the OGRGeomFieldDefn Those settings are used to round the coordinates of the geometry of the features to an appropriate decimal precision.

注釈

The COORDINATE_PRECISION_GEOMETRY or COORDINATE_PRECISION_PLACE layer creation option has precedence over the values set on the OGRGeomFieldDefn.

Implementation details: the coordinate precision is stored as xy_coordinate_resolution_place and z_coordinate_resolution_place members at the FeatureCollection level, for the geometries written in the place element. Their numeric value is expressed in the units of the SRS.

For the geometry standard GeoJSON element, the coordinate precision is stored as xy_coordinate_resolution and z_coordinate_resolution members, and their numeric value is expressed in the units of the OGC:CRS84 SRS (hence decimal degrees for xy_coordinate_resolution)

Example:

{
    "type": "FeatureCollection",
    "xy_coordinate_resolution_place": 1.0,
    "z_coordinate_resolution_place": 1.0,
    "xy_coordinate_resolution": 8.9e-6,
    "z_coordinate_resolution": 1e-1,
    "features": []
}