Merge PR#144 to draft-1.5 from hobu/wkt-updates

Removed support for geotiff CRS definitions. (#104) 
All OGC WKT definitions are now valid. (#95, #129)

Author: esilvia

.readthedocs.yaml

@@ -0,0 +1,27 @@
+# .readthedocs.yaml
+# Read the Docs configuration file
+# See https://docs.readthedocs.io/en/stable/config-file/v2.html for details
+
+# Required
+version: 2
+
+build:
+  os: "ubuntu-lts-latest"
+  tools:
+    python: "mambaforge-latest"
+
+sphinx:
+  builder: html
+  configuration: source/conf.py
+  fail_on_warning: false
+
+python:
+  install:
+    - requirements: source/requirements.txt
+
+conda:
+  environment: source/environment.yml
+
+formats:
+  - pdf
+  - epub

source/01_intro.txt

@@ -32,10 +32,16 @@ The additions of LAS 1.5 include:
 * Backward compatibility with LAS 1.1 – LAS 1.4.
 * LAS 1.5 mode which supports:
 
+  * Removed support for PDRFs 0-5.
+    (`I-128 <https://github.com/ASPRSorg/LAS/issues/128>`_)
   * Added Max/Min GPS Time fields to header block.
     (`I-118 <https://github.com/ASPRSorg/LAS/issues/118>`_)
   * Added Offset GPS Time definition.
     (`I-6 <https://github.com/ASPRSorg/LAS/issues/6>`_)
+  * CRS support expanded to all published WKT versions, removing support for GeoTIFF CRS encoding.
+    (`I-95 <https://github.com/ASPRSorg/LAS/issues/95>`_,
+    `I-104 <https://github.com/ASPRSorg/LAS/issues/104>`_,
+    `I-129 <https://github.com/ASPRSorg/LAS/issues/129>`_)
   * Clarify requirement that the Extra Bytes VLR must be unique.
     (`I-150 <https://github.com/ASPRSorg/LAS/issues/150>`_)
 

source/02.04_header.sub

@@ -182,11 +182,10 @@ a value of 1). This bit field is defined as:
     |       |                       | multiple returns.                        |
     +-------+-----------------------+------------------------------------------+
     | 4     | WKT                   | If set, the Coordinate Reference System  |
-    |       |                       | (CRS) is WKT. If not set, the CRS is     |
-    |       |                       | GeoTIFF. It should not be set if the     |
-    |       |                       | file writer wishes to ensure legacy      |
-    |       |                       | compatibility (which means the CRS must  |
-    |       |                       | be GeoTIFF).                             |
+    |       |                       | (CRS) is WKT. This bit must be set in    |
+    |       |                       | LAS 1.5; GeoTIFF CRS definitions are not |
+    |       |                       | supported for legacy                     |
+    |       |                       | compatibility beginning with LAS 1.5.    |
     +-------+-----------------------+------------------------------------------+
     | 5     | Reserved              | Must be set to zero (0).                 |
     +-------+-----------------------+------------------------------------------+
@@ -446,7 +445,7 @@ The Time Offset field can be used to optimize :ref:`GPS Time <gpstime_link>` pre
 Offset GPS Time for a point record is equal to standard GPS Time, minus :math:`10^6` * Time Offset.
 
 For example, Adjusted Standard GPS Time uses a total offset of 1 billion (:math:`10^9`) seconds, which would be specified by a Time Offset of 1000.
-This achieves 100 nanosecond precision for the years 2007-2015. The LAS wiki provides 
+This achieves 100 nanosecond precision for the years 2007-2015. The LAS wiki provides
 `recommended values <https://github.com/ASPRSorg/LAS/wiki/Suggested-LAS-1.5-Time-Offset-Values>`_
 and year ranges that users are encouraged to use to maximize compatibility between datasets.
 

source/03_crs.txt

@@ -0,0 +1,79 @@
+.. raw:: latex
+
+    \newpage
+
+Coordinate Reference System
+--------------------------------------------------------------------------------
+
+Coordinate Reference System (CRS) information is required for a LAS 1.5 file.
+LAS 1.5 defines VLRs in :ref:`vlrdef_label` and EVLRs in :ref:`evlrdef_label` 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 <https://www.ogc.org/standard/wkt-crs/>`__ (WKT) without regard to
+the :ref:`Global Encoding <globalencoding_link>` bit.
+
+GeoTIFF CRS representations are no longer supported as of LAS 1.5.
+
+.. _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 consistent with the same WKT
+specification being used by :ref:`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.

source/03_required_vlrs.txt

@@ -2,7 +2,9 @@
 
     \newpage
 
-Other Specification Defined VLRs (Optional)
+.. _optional_vlrs:
+
+Optional VLR Definitions
 --------------------------------------------------------------------------------
 
 Classification Lookup