3. Coordinate Reference System

Coordinate Reference System (CRS) information is required for a LAS 1.5 file. LAS 1.5 defines VLRs in Variable Length Records (VLRs) and EVLRs in Extended Variable Length Records (EVLRs) and requires them for specifying the Coordinate Reference System (CRS) of the file.

CRS information shall be placed in VLRs or EVLRs and represented as OGC Well Known Text (WKT) without regard to the Global Encoding bit.

GeoTIFF CRS representations are no longer supported as of LAS 1.5.

3.1. 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 If an EVLR is to override an already existing CRS VLR, writers should also write a Superseded VLR to label it.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 - Commonly called “WKT2” or “WKTv2” and is the most current version of WKT as of this publication.

  • 18-010r7 - 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 - 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.

3.2. 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 consistent with the same WKT specification being used by OGC Coordinate System WKT Record (Required), 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.