FlatGeobuf Class

The reader reads the points, lines, polygons, their multi-geometries and the geometry collections, with their altitudes (Z) and their measures (M, a NaN value being no measure); the T and TM values are dropped, as the format does not define their meaning, and the curves, surfaces and triangles throw a FormatException. The collection is named after the name of the header. The property values have the .NET type of their column: a SByte, Byte, Boolean, Int16, UInt16, Int32, UInt32, Int64, UInt64, Single, Double, a String, a JsonElement for a JSON column (or the text when it is not valid JSON), a DateTimeOffset for a date-time column (a time without offset is UTC, and a value that cannot be parsed is kept as text) and an array of bytes for a binary column. The features have no identifier. The coordinate system of the header is not read: the coordinates are expected to be longitudes and latitudes.

The writer writes the header with the name of the collection, its bounds, the coordinate system EPSG:4326 (WGS 84), one geometry type when every geometry has the same type (else each geometry gets its type), and Z values when a position has an altitude (the positions without altitude get 0), and M values when a position has a measure (the positions without measure get NaN). The times of the positions are not written. The columns are the property names in the order they are first seen; a column gets the type of its values, Int64 for integers of different types, Double for numbers of different types, and the text of the values for other mixes. A date, a DateTime or a DateTimeOffset is a date-time column in ISO 8601, to the millisecond (GDAL reads at most 32 characters), an array of bytes a binary column, a JsonElement object or array a JSON column, and other values a string column of their text. A null value is not written. A feature without geometry, or with an empty one, is written without geometry. The identifiers of the features are not written.

With the spatial index, the default, the features are written along a Hilbert curve, the order of the index, and not in the order of the collection; the index is not written when a feature has no geometry.