# Package org.apache.sis.io.wkt

Well Known Text (WKT) parsing and formatting.

See: Description

- Interface Summary
  Interface | Description
  --- | ---
  Parser | A parser or a factory capable to create an object from a string in the WKT format.

- Class Summary
  Class | Description
  --- | ---
  Colors | The colors to use for formatting Well Known Text (WKT) objects.
  FormattableObject | Base class for objects that can be formatted as Well Known Text (WKT).
  Formatter | Provides support methods for formatting a Well Known Text (WKT).
  Symbols | The set of symbols to use for Well Known Text (WKT) parsing and formatting.
  Transliterator | Controls the replacement of characters, abbreviations and names between the objects in memory and their WKT representations.
  Warnings | Warnings that occurred during a Well Known Text (WKT) parsing or formatting.
  WKTFormat | Parser and formatter for Well Known Text (WKT) strings.

- Enum Summary
  Enum | Description
  --- | ---
  Convention | The convention to use for WKT formatting.
  ElementKind | Kind of an element in a Well Known Text.
  KeywordCase | Whether WKT keywords shall be written with lower, upper or camel case styles.
  KeywordStyle | Whether to use short or long WKT keywords.

- Exception Summary
  Exception | Description
  --- | ---
  UnformattableObjectException | Thrown by `FormattableObject​.toWKT()` when an object can not be formatted as WKT.
  UnparsableObjectException | Thrown when a Well Known Text (WKT) can not be parsed.

## Package org.apache.sis.io.wkt Description

Well Known Text (WKT) parsing and formatting. This package implements the services provided by various convenience methods:

- `CRS​.fromWKT(String)` (SIS parsing static method)
- `CRSFactory​.createFromWKT(String)` (GeoAPI parsing method)
- `MathTransformFactory​.createFromWKT(String)` (GeoAPI parsing method)
- `IdentifiedObject​.toWKT()` (GeoAPI formatting method)

However the `WKTFormat` class provided in this package gives more control. For example this package allows to:

- Format projection and parameters using the names of a chosen authority. For example the "Mercator (variant A)" projection is named `"Mercator_1SP"` by OGC 01-009 and `"CT_Mercator"` by GeoTIFF.
- Format the elements with different quote characters or brackets style. For example both `ID["EPSG",4326]` and `ID("EPSG",4326)` are legal WKT.
- Format with a different indentation or format the whole WKT on a single line.
- Apply syntactic coloring on terminal supporting ANSI escape codes (a.k.a. ECMA-48, ISO/IEC 6429 and X3.64).
- Alter the parsing in a way compatible with non-standard (but commonly used) WKT. For example some others software products ignore the `AXIS[…]` elements at parsing time.
- Report warnings that occurred during parsing or formatting.

Referencing WKT
Referencing WKT is defined using Extended Backus Naur Form (EBNF) in two versions:

- ISO 19162 defines the current format, also known as “WKT 2”. The specification is also made available online by OGC.
- The previous format — “WKT 1” — was defined in the OGC document 01-009. This definition is shown on GeoAPI.

The WKT 1 format has been interpreted differently by various implementors. One noticeable difference is the unit of measurement of prime meridians and projection parameters. The WKT 2 format aims to solve the inter-operability problem caused by such mismatches, but not all software products support this new format. Consequently importing or exporting data from/to a software with the WKT syntax require knowledge of the WKT variant used by that software. This variant can be specified by the `Convention` enumeration.
Geometry WKT
The `GeneralEnvelope` and `GeneralDirectPosition` classes provide their own, limited, WKT parsing and formatting services for the `BOX` and `POINT` elements. A description for this WKT format can be found on Wikipedia.
Where to find WKT examples
An excellent source of well-formed WKT is the online EPSG Geodetic Parameter Registry. The WKT of many Coordinate Reference System object can be viewed using the pattern below (replace `3395` by the EPSG code of the desired CRS):

> Example: "WGS 84 / World Mercator": http://epsg-registry.org/export.htm?wkt=urn:ogc:def:crs:EPSG::3395

Readers should be aware that some popular other sources of WKT are actually invalid, since many of them do not comply with EPSG definitions (especially on axis order). The above-cited EPSG registry is the authoritative source of CRS definitions in the EPSG namespace.

Since:
  0.4
See Also:
  WKT 2 specification, Legacy WKT 1

Defined in the `sis-metadata` module

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