org.locationtech.jts.io

Class WKBReader

java.lang.Object

org.locationtech.jts.io.WKBReader

public class WKBReader
extends Object

Reads a Geometryfrom a byte stream in Well-Known Binary format. Supports use of an InStream, which allows easy use with arbitrary byte stream sources.

This class reads the format describe in WKBWriter. It partially handles the Extended WKB format used by PostGIS, by parsing and storing optional SRID values. If a SRID is not specified in an element geometry, it is inherited from the parent's SRID. The default SRID value is 0.

Although not defined in the WKB specification, empty points are handled if they are represented as a Point with NaN X and Y ordinates.

The reader repairs structurally-invalid input (specifically, LineStrings and LinearRings which contain too few points have vertices added, and non-closed rings are closed).

The reader handles most errors caused by malformed or malicious WKB data. It checks for obviously excessive values of the fields numElems, numRings, and numCoords. It also checks that the reader does not read beyond the end of the data supplied. A ParseException is thrown if this situation is detected.

This class is designed to support reuse of a single instance to read multiple geometries. This class is not thread-safe; each thread should create its own instance.

As of version 1.15, the reader can read geometries following the OGC 06-103r4 Simple Features Access 1.2.1 specification, which aligns with the ISO 19125 standard. This format is used by Spatialite and Geopackage.

The difference between PostGIS EWKB format and the new ISO/OGC specification is that Z and M coordinates are detected with a bit mask on the higher byte in the former case (0x80 for Z and 0x40 for M) while new OGC specification use specific int ranges for 2D geometries, Z geometries (2D code+1000), M geometries (2D code+2000) and ZM geometries (2D code+3000).

Note that the WKBWriter is not changed and still writes the PostGIS EWKB geometry format.

See Also:

for a formal format specification

Constructor Summary

Constructors

Constructor and Description
WKBReader()
WKBReader(GeometryFactory geometryFactory)

Method Summary

Modifier and Type	Method and Description
static byte[]	hexToBytes(String hex) Converts a hexadecimal string to a byte array.
Geometry	read(byte[] bytes) Reads a single Geometry in WKB format from a byte array.
Geometry	read(InStream is) Reads a Geometry in binary WKB format from an InStream.

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

WKBReader

public WKBReader()

WKBReader

public WKBReader(GeometryFactory geometryFactory)

Method Detail

hexToBytes

public static byte[] hexToBytes(String hex)

Converts a hexadecimal string to a byte array. The hexadecimal digit symbols are case-insensitive.

Parameters:

hex - a string containing hex digits

Returns:

an array of bytes with the value of the hex string

read

public Geometry read(byte[] bytes)
              throws ParseException

Reads a single Geometry in WKB format from a byte array.

Parameters:

bytes - the byte array to read from

Returns:

the geometry read

Throws:

ParseException - if the WKB is ill-formed

read

public Geometry read(InStream is)
              throws IOException,
                     ParseException

Reads a Geometry in binary WKB format from an InStream.

Parameters:

is - the stream to read from

Returns:

the Geometry read

Throws:

IOException - if the underlying stream creates an error

ParseException - if the WKB is ill-formed