.. raw:: latex

    \newpage

.. _crs_label:

Coordinate Reference System
--------------------------------------------------------------------------------

Coordinate Reference System (CRS) information is required for a LAS 1.5 file
and must be placed in :ref:`vlrdef_label` or :ref:`evlrdef_label`.
LAS 1.5 CRS information shall be represented as `OGC Well
Known Text <https://www.ogc.org/standard/wkt-crs/>`__ (WKT), as indicated by
the :ref:`Global Encoding <globalencoding_link>` bit.

GeoTIFF CRS representations from prior versions of LAS are not supported in LAS 1.5.

It is considered a file error to have more than one WKT VLR or EVLR in the file.
A writer can efficiently revise a CRS definition without rewriting the entire LAS file by
"superseding" the existing CRS VLR or EVLR and appending a new CRS definition in an EVLR. 
Superseding is performed by changing the
Record ID of the VLR or EVLR to match the :ref:`superseded_vlr_label` VLR definition.

.. _crs_wkt:

OGC Coordinate System WKT Record (Required)
................................................................................

The WKT record is **required** and can be specified as either a VLR or an
EVLR. If an EVLR is to override an already existing CRS VLR, writers
should also write a :ref:`Superseded VLR <superseded_vlr_label>` to label it.

+-----------------+-----------------------------+
| User ID         | LASF_Projection             |
+-----------------+-----------------------------+
| Record ID       | 2112                        |
+-----------------+-----------------------------+

This record must contain the textual data representing a WKT as defined by any
published OGC Well Known Text standard with the following considerations:

* The OGC Coordinate System WKT VLR data shall be a null-terminated string.
* The OGC Coordinate System WKT VLR data shall be considered UTF-8.
* The OGC Coordinate System WKT VLR data shall be considered C locale-based with
  no localization of the numeric strings within the WKT being performed.


.. note::

  Any published version of an OGC WKT standard is a valid definition for LAS 1.5.
  OGC has published multiple versions of WKT, including the following noteworthy versions:

  * `18-010r11 <https://docs.ogc.org/is/18-010r11/18-010r11.pdf>`__ - Commonly called "WKT2"
    or "WKTv2" and is the most current version of WKT as of this publication.
  * `18-010r7 <https://docs.ogc.org/is/18-010r11/18-010r11.pdf>`__ - This variant of "WKT2"
    added support for the definition of ``EPOCH`` for  defining the date against which 
    coordinates in the LAS file are referenced in a dynamic coordinate reference system.
  * `12-063r5 <https://portal.opengeospatial.org/files/12-063r5>`__ - 
    Commonly called "WKT1" and the formally ratified variant of WKT that was used
    for LAS 1.4.

  If OGC were to publish a new WKT standard, it would also be a
  valid definition for LAS 1.5.

.. _math_wkt:

OGC Math Transform WKT Record (Optional)
................................................................................

Writers may include an optional OGC Math Transform WKT Record to provide a
supplemental parameterized math transform definition.

+-----------------+-----------------------------+
| User ID         | LASF_Projection             |
+-----------------+-----------------------------+
| Record ID       | 2111                        |
+-----------------+-----------------------------+

This record must contain a Math Transform WKT Record consistent with the same WKT
specification being used by the :ref:`Coordinate System WKT Record <crs_wkt>`, with the following considerations:

* The OGC Math Transform WKT VLR data shall be a null-terminated string.
* The OGC Math Transform WKT VLR data shall be considered UTF-8.
* The OGC Math Transform WKT VLR data shall be considered C locale-based, and
  no localization of the numeric strings within the WKT should be performed.